Prof. Dr. Jonathan Finley
Academic Research Focus
- Growth and Functional Properties of Ultrapure Nanomaterials: III-V semiconductor nanostructures (nanowires, QD-nanostructures), 2D-nanomaterials and diamond grown using methods such as MBE and CVD
- Heterostructures of 2D-Materials: two-dimensional materials such as graphene, transition metal dichalcogenides and layered perovskites and the exploration of their novel optical, electronic and magnetic properties
- Quantum Sensing: development of quantum sensors with a particular focus on applications in the life-sciences and ultra-sensitive photon detection at the quantum limit
- Heterostructures of 2D-Materials: two-dimensional materials such as graphene, transition metal dichalcogenides and layered perovskites and the exploration of their novel optical, electronic and magnetic properties
- Quantum Sensing: development of quantum sensors with a particular focus on applications in the life-sciences and ultra-sensitive photon detection at the quantum limit
Fields of Application
Nanomaterials, Photonics, Semiconductor Materials, Sensor Technology
Publications
74.
E Blundo, N H T Schmidt, A V Stier, J J Finley
Identification of Hexagonal Boron Nitride Thickness on SiO2/Si Substrates by Colorimetry and Contrast Journal Article
In: Applied Sciences-Basel, vol. 15, no. 15, 2025.
@article{nokey,
title = {Identification of Hexagonal Boron Nitride Thickness on SiO2/Si Substrates by Colorimetry and Contrast},
author = {E Blundo and N H T Schmidt and A V Stier and J J Finley},
url = {\<Go to ISI\>://WOS:001549028800001},
doi = {10.3390/app15158400},
year = {2025},
date = {2025-07-29},
journal = {Applied Sciences-Basel},
volume = {15},
number = {15},
abstract = {Hexagonal boron nitride (hBN) is a layered material with a wide variety of excellent properties for emergent applications in quantum photonics using atomically thin materials. For example, it hosts single-photon emitters that operate up to room-temperature, it can be exploited for atomically flat tunnel barriers, and it can be used to form high finesse photonic nanocavities. Moreover, it is an ideal encapsulating dielectric for two-dimensional (2D) materials and heterostructures, with highly beneficial effects on their electronic and optical properties. Depending on the use case, the thickness of hBN is a critical parameter and needs to be carefully controlled from the monolayer to hundreds of layers. This calls for quick and non-invasive methods to unambiguously identify the thickness of exfoliated flakes. Here, we show that the apparent color of hBN flakes on different SiO2/Si substrates can be made to be highly indicative of the flake thickness, providing a simple method to infer the hBN thickness. Using experimental determination of the colour of hBN flakes and calculating the optical contrast, we derived the optimal substrates for the most reliable hBN thickness identification for flakes with thickness ranging from a few layers towards bulk-like hBN. Our results offer a practical guide for the determination of hBN flake thickness for widespread applications using 2D materials and heterostructures.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Hexagonal boron nitride (hBN) is a layered material with a wide variety of excellent properties for emergent applications in quantum photonics using atomically thin materials. For example, it hosts single-photon emitters that operate up to room-temperature, it can be exploited for atomically flat tunnel barriers, and it can be used to form high finesse photonic nanocavities. Moreover, it is an ideal encapsulating dielectric for two-dimensional (2D) materials and heterostructures, with highly beneficial effects on their electronic and optical properties. Depending on the use case, the thickness of hBN is a critical parameter and needs to be carefully controlled from the monolayer to hundreds of layers. This calls for quick and non-invasive methods to unambiguously identify the thickness of exfoliated flakes. Here, we show that the apparent color of hBN flakes on different SiO2/Si substrates can be made to be highly indicative of the flake thickness, providing a simple method to infer the hBN thickness. Using experimental determination of the colour of hBN flakes and calculating the optical contrast, we derived the optimal substrates for the most reliable hBN thickness identification for flakes with thickness ranging from a few layers towards bulk-like hBN. Our results offer a practical guide for the determination of hBN flake thickness for widespread applications using 2D materials and heterostructures.
73.
H Esmaielpour, P Schmiedeke, N Isaev, C Doganlar, M Döblinger, J J Finley, G Koblmüller
Hot carrier dynamics in III–V semiconductor nanowires under dominant radiative and Auger recombination Journal Article
In: Applied Physics Letters, vol. 126, no. 8, pp. 083505, 2025, ISSN: 0003-6951.
@article{nokey,
title = {Hot carrier dynamics in III\textendashV semiconductor nanowires under dominant radiative and Auger recombination},
author = {H Esmaielpour and P Schmiedeke and N Isaev and C Doganlar and M D\"{o}blinger and J J Finley and G Koblm\"{u}ller},
url = {https://doi.org/10.1063/5.0248247},
doi = {10.1063/5.0248247},
issn = {0003-6951},
year = {2025},
date = {2025-02-24},
journal = {Applied Physics Letters},
volume = {126},
number = {8},
pages = {083505},
abstract = {One-dimensional structures such as nanowires (NWs) show great promise in tailoring the rates of hot carrier thermalization in semiconductors with important implications for the design of efficient hot carrier absorbers. However, the fabrication of defect-free crystal structures and control of their intrinsic electronic properties can be challenging, raising concerns about the role of competing radiative and non-radiative recombination mechanisms that govern hot carrier effects. Here, we elucidate the impact of crystal purity and altered electronic properties on the hot carrier properties by comparing two classes of III\textendashV semiconductor NW arrays with similar bandgap energies and geometries, yet different crystal quality: one composed of GaAsSb NWs, which host antisite point defects but are free of planar stacking defects, and the other InGaAs NWs with a very high density of stacking defects. Photoluminescence spectroscopy demonstrates distinct hot carrier effects in both NW arrays; however, the InGaAs NWs exhibit stronger hot carrier effects, as evidenced by increased carrier temperature under identical photo-absorptivity. This difference arises from higher rates of Auger recombination in the InGaAs NWs due to their increased n-type conductivity, as confirmed by excitation power-dependent measurements. Our findings suggest that while enhancing material properties is crucial for improving the performance of hot carrier absorbers, optimizing conditions to increase the rates of Auger recombination will further boost the efficiency of these devices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
One-dimensional structures such as nanowires (NWs) show great promise in tailoring the rates of hot carrier thermalization in semiconductors with important implications for the design of efficient hot carrier absorbers. However, the fabrication of defect-free crystal structures and control of their intrinsic electronic properties can be challenging, raising concerns about the role of competing radiative and non-radiative recombination mechanisms that govern hot carrier effects. Here, we elucidate the impact of crystal purity and altered electronic properties on the hot carrier properties by comparing two classes of III–V semiconductor NW arrays with similar bandgap energies and geometries, yet different crystal quality: one composed of GaAsSb NWs, which host antisite point defects but are free of planar stacking defects, and the other InGaAs NWs with a very high density of stacking defects. Photoluminescence spectroscopy demonstrates distinct hot carrier effects in both NW arrays; however, the InGaAs NWs exhibit stronger hot carrier effects, as evidenced by increased carrier temperature under identical photo-absorptivity. This difference arises from higher rates of Auger recombination in the InGaAs NWs due to their increased n-type conductivity, as confirmed by excitation power-dependent measurements. Our findings suggest that while enhancing material properties is crucial for improving the performance of hot carrier absorbers, optimizing conditions to increase the rates of Auger recombination will further boost the efficiency of these devices.
72.
K Barthelmi, T Amit, L Sigl, M Troue, T Klokkers, A Herrmann, T Taniguchi, K Watanabe, J J Finley, C Kastl, S Refaely-Abramson, A W Holleitner
Spectrally resolved far-field emission pattern of single photon emitters in $mathrmMomathrmS_2$ Journal Article
In: Physical Review Materials, vol. 9, no. 1, pp. 016201, 2025.
@article{nokey,
title = {Spectrally resolved far-field emission pattern of single photon emitters in $mathrmMomathrmS_2$},
author = {K Barthelmi and T Amit and L Sigl and M Troue and T Klokkers and A Herrmann and T Taniguchi and K Watanabe and J J Finley and C Kastl and S Refaely-Abramson and A W Holleitner},
url = {https://link.aps.org/doi/10.1103/PhysRevMaterials.9.016201},
doi = {10.1103/PhysRevMaterials.9.016201},
year = {2025},
date = {2025-01-08},
urldate = {2025-01-08},
journal = {Physical Review Materials},
volume = {9},
number = {1},
pages = {016201},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
71.
P Moser, L M Wolz, A Henning, A Thurn, M Kuhl, P Ji, P Soubelet, M Schalk, J Eichhorn, I D Sharp, A V Stier, J J Finley
Atomically Flat Dielectric Patterns for Bandgap Engineering and Lateral Junction Formation in MoSe2 Monolayers Journal Article
In: Advanced Functional Materials, vol. n/a, no. n/a, pp. 2418528, 2024, ISSN: 1616-301X.
@article{nokey,
title = {Atomically Flat Dielectric Patterns for Bandgap Engineering and Lateral Junction Formation in MoSe2 Monolayers},
author = {P Moser and L M Wolz and A Henning and A Thurn and M Kuhl and P Ji and P Soubelet and M Schalk and J Eichhorn and I D Sharp and A V Stier and J J Finley},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202418528},
doi = {https://doi.org/10.1002/adfm.202418528},
issn = {1616-301X},
year = {2024},
date = {2024-12-23},
journal = {Advanced Functional Materials},
volume = {n/a},
number = {n/a},
pages = {2418528},
abstract = {Abstract Combining a precise sputter etching method with subsequent AlOx growth within an atomic layer deposition chamber enables the fabrication of atomically flat lateral patterns of SiO2 and AlOx. The transfer of MoSe2 monolayers onto these dielectrically modulated substrates results in the formation of lateral heterojunctions due to the interaction with alternating regions of SiO2 and AlOx, with the flat substrate topography leading to minimal strain across the junction. Kelvin probe force microscopy measurements show significant variations in the contact potential difference (CPD) across the interface, with AlOx regions inducing a 230 mV increase in CPD. Photoluminescence spectroscopy reveals shifts in spectral weight of neutral and charged exciton species across the different dielectric regions. On the AlOx side, the Fermi energy moves closer to the conduction band, leading to a higher trion-to-exciton ratio, indicating a bandgap shift consistent with CPD changes. In addition, transient reflection spectroscopy highlights the influence of the dielectric environment on carrier dynamics, with the SiO2 side exhibiting rapid carrier decay typical of neutral exciton recombination. In contrast, the AlOx side shows slower, mixed decay behavior consistent with conversion of trions back into excitons. These results demonstrate how dielectric substrate engineering can tune 2D materials, allowing scalable fabrication of advanced junctions for novel (opto)electronics applications.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Combining a precise sputter etching method with subsequent AlOx growth within an atomic layer deposition chamber enables the fabrication of atomically flat lateral patterns of SiO2 and AlOx. The transfer of MoSe2 monolayers onto these dielectrically modulated substrates results in the formation of lateral heterojunctions due to the interaction with alternating regions of SiO2 and AlOx, with the flat substrate topography leading to minimal strain across the junction. Kelvin probe force microscopy measurements show significant variations in the contact potential difference (CPD) across the interface, with AlOx regions inducing a 230 mV increase in CPD. Photoluminescence spectroscopy reveals shifts in spectral weight of neutral and charged exciton species across the different dielectric regions. On the AlOx side, the Fermi energy moves closer to the conduction band, leading to a higher trion-to-exciton ratio, indicating a bandgap shift consistent with CPD changes. In addition, transient reflection spectroscopy highlights the influence of the dielectric environment on carrier dynamics, with the SiO2 side exhibiting rapid carrier decay typical of neutral exciton recombination. In contrast, the AlOx side shows slower, mixed decay behavior consistent with conversion of trions back into excitons. These results demonstrate how dielectric substrate engineering can tune 2D materials, allowing scalable fabrication of advanced junctions for novel (opto)electronics applications.
70.
H Esmaielpour, P Schmiedeke, N Isaev, C Doganlar, M Döblinger, J J Finley, G Koblmüller
Competing mechanisms of dominant radiative and Auger recombination in hot carrier generation in III-V semiconductor nanowires Journal Article
In: arXiv preprint arXiv:2411.07822, 2024.
@article{nokey,
title = {Competing mechanisms of dominant radiative and Auger recombination in hot carrier generation in III-V semiconductor nanowires},
author = {H Esmaielpour and P Schmiedeke and N Isaev and C Doganlar and M D\"{o}blinger and J J Finley and G Koblm\"{u}ller},
year = {2024},
date = {2024-11-12},
journal = {arXiv preprint arXiv:2411.07822},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
69.
C Qian, V Villafañe, P Soubelet, P Ji, A V Stier, J J Finley
Probing Dark Excitons in Monolayer $mathrmMoS_2$ by Nonlinear Two-Photon Spectroscopy Journal Article
In: Physical Review Letters, vol. 133, no. 8, pp. 086902, 2024.
@article{nokey,
title = {Probing Dark Excitons in Monolayer $mathrmMoS_2$ by Nonlinear Two-Photon Spectroscopy},
author = {C Qian and V Villafa\~{n}e and P Soubelet and P Ji and A V Stier and J J Finley},
url = {https://link.aps.org/doi/10.1103/PhysRevLett.133.086902},
doi = {10.1103/PhysRevLett.133.086902},
year = {2024},
date = {2024-08-21},
journal = {Physical Review Letters},
volume = {133},
number = {8},
pages = {086902},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
68.
P Soubelet, A Delhomme, A V Stier, J J Finley
Polarons shape the interlayer exciton emission of MoSe $ _2 $/WSe $ _2 $ heterobilayers Journal Article
In: arXiv preprint arXiv:2407.15649, 2024.
@article{nokey,
title = {Polarons shape the interlayer exciton emission of MoSe $ _2 $/WSe $ _2 $ heterobilayers},
author = {P Soubelet and A Delhomme and A V Stier and J J Finley},
year = {2024},
date = {2024-07-22},
journal = {arXiv preprint arXiv:2407.15649},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
67.
T Schreitmüller, D Kumar Saluja, C E Mead, M Ramsteiner, H W Jeong, H Esmaielpour, C Huang, D Ruhstorfer, J J Finley, L J Lauhon, G Koblmüller
Spatial dependence of dopant incorporation and electrical transport in Si-doped GaAs(Sb) nanowires Journal Article
In: Physical Review Materials, vol. 8, no. 7, pp. 076002, 2024.
@article{nokey,
title = {Spatial dependence of dopant incorporation and electrical transport in Si-doped GaAs(Sb) nanowires},
author = {T Schreitm\"{u}ller and D Kumar Saluja and C E Mead and M Ramsteiner and H W Jeong and H Esmaielpour and C Huang and D Ruhstorfer and J J Finley and L J Lauhon and G Koblm\"{u}ller},
url = {https://link.aps.org/doi/10.1103/PhysRevMaterials.8.076002},
doi = {10.1103/PhysRevMaterials.8.076002},
year = {2024},
date = {2024-07-15},
journal = {Physical Review Materials},
volume = {8},
number = {7},
pages = {076002},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
66.
H Esmaielpour, N Isaev, J J Finley, G Koblmüller
Influence of Auger heating and Shockley-Read-Hall recombination on hot-carrier dynamics in InGaAs nanowires Journal Article
In: Physical Review B, vol. 109, no. 23, pp. 235303, 2024.
@article{nokey,
title = {Influence of Auger heating and Shockley-Read-Hall recombination on hot-carrier dynamics in InGaAs nanowires},
author = {H Esmaielpour and N Isaev and J J Finley and G Koblm\"{u}ller},
url = {https://link.aps.org/doi/10.1103/PhysRevB.109.235303},
doi = {10.1103/PhysRevB.109.235303},
year = {2024},
date = {2024-06-20},
journal = {Physical Review B},
volume = {109},
number = {23},
pages = {235303},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
65.
P Schmiedeke, C Doganlar, H W Jeong, M Döblinger, J J Finley, G Koblmüller
Low-threshold single ternary GaAsSb nanowire lasers emitting at silicon transparent wavelengths Journal Article
In: Applied Physics Letters, vol. 124, no. 7, pp. 071112, 2024, ISSN: 0003-6951.
@article{nokey,
title = {Low-threshold single ternary GaAsSb nanowire lasers emitting at silicon transparent wavelengths},
author = {P Schmiedeke and C Doganlar and H W Jeong and M D\"{o}blinger and J J Finley and G Koblm\"{u}ller},
url = {https://doi.org/10.1063/5.0191070},
doi = {10.1063/5.0191070},
issn = {0003-6951},
year = {2024},
date = {2024-02-12},
journal = {Applied Physics Letters},
volume = {124},
number = {7},
pages = {071112},
abstract = {Conventional binary III\textendashV nanowire (NW) lasers face substantial challenges in tuning their lasing emission to silicon transparent wavelengths and require complex quantum heterostructure designs for realizing on-chip integrated nanolasers. Here, an alternative and straightforward approach is reported by developing ternary III\textendashV NW-lasers in the form of surface-passivated GaAsSb NW-lasers grown on silicon. High-quality GaAsSb NW-cavities with high Sb-content (\>20%) and extended lengths (\>5 μm) are shown to exhibit striking radiative efficiency enhancements (∼200-fold) when passivated by closely lattice-matched InAlGaAs shell layers. Utilizing this core\textendashshell approach, optically pumped lasing is then demonstrated from single GaAsSb NW-lasers with lasing threshold as low as 3.2 μJ/cm2 at temperatures up to 250 K and emission wavelengths of ∼1.1\textendash1.2 μm. Analysis of the optical mode spectra and mode-dependent threshold gain further shows that lasing is induced by the fundamental HE11 modes, and likely even lower thresholds may be achieved by establishing the TE01 mode at increased NW-cavity diameters.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Conventional binary III–V nanowire (NW) lasers face substantial challenges in tuning their lasing emission to silicon transparent wavelengths and require complex quantum heterostructure designs for realizing on-chip integrated nanolasers. Here, an alternative and straightforward approach is reported by developing ternary III–V NW-lasers in the form of surface-passivated GaAsSb NW-lasers grown on silicon. High-quality GaAsSb NW-cavities with high Sb-content (>20%) and extended lengths (>5 μm) are shown to exhibit striking radiative efficiency enhancements (∼200-fold) when passivated by closely lattice-matched InAlGaAs shell layers. Utilizing this core–shell approach, optically pumped lasing is then demonstrated from single GaAsSb NW-lasers with lasing threshold as low as 3.2 μJ/cm2 at temperatures up to 250 K and emission wavelengths of ∼1.1–1.2 μm. Analysis of the optical mode spectra and mode-dependent threshold gain further shows that lasing is induced by the fundamental HE11 modes, and likely even lower thresholds may be achieved by establishing the TE01 mode at increased NW-cavity diameters.
64.
H Esmaielpour, N Isaev, I Makhfudz, M Döblinger, J J Finley, G Koblmüller
Strong Dimensional and Structural Dependencies of Hot Carrier Effects in InGaAs Nanowires: Implications for Photovoltaic Solar Cells Journal Article
In: ACS Applied Nano Materials, vol. 7, no. 3, pp. 2817-2824, 2024.
@article{nokey,
title = {Strong Dimensional and Structural Dependencies of Hot Carrier Effects in InGaAs Nanowires: Implications for Photovoltaic Solar Cells},
author = {H Esmaielpour and N Isaev and I Makhfudz and M D\"{o}blinger and J J Finley and G Koblm\"{u}ller},
url = {https://doi.org/10.1021/acsanm.3c05041},
doi = {10.1021/acsanm.3c05041},
year = {2024},
date = {2024-02-09},
journal = {ACS Applied Nano Materials},
volume = {7},
number = {3},
pages = {2817-2824},
abstract = {III\textendashV nanowire structures are among the promising material systems with applications in hot carrier solar cells. These nanostructures can meet the requirements for such photovoltaic devices, i.e., the suppression of thermalization loss, an efficient hot carrier transport, and enhanced photoabsorption thanks to their unique one-dimensional (1D) geometry and density-of-states. Here, we investigate the effects of spatial confinement of photogenerated hot carriers in InGaAs-InAlAs core\textendashshell nanowires, which presents an ideal class of hot carrier solar cell materials due to its suitable electronic properties. Using steady-state photoluminescence spectroscopy, our study reveals that by increasing the degree of spatial confinement and Auger recombination, the effects of hot carriers increase, which is in good agreement with theoretical modeling. However, for thin nanowires, the temperature of hot carriers decreases as the effects of crystal disorder increase. This observation is confirmed by probing the extent of the disorder-induced Urbach tail and linked to the presence of a higher density of stacking defects in the limit of thin nanowires. These findings expand our knowledge of hot carrier thermalization in nanowires, which can be applied for designing efficient 1D hot carrier absorbers for advanced-concept photovoltaic solar cells.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
III–V nanowire structures are among the promising material systems with applications in hot carrier solar cells. These nanostructures can meet the requirements for such photovoltaic devices, i.e., the suppression of thermalization loss, an efficient hot carrier transport, and enhanced photoabsorption thanks to their unique one-dimensional (1D) geometry and density-of-states. Here, we investigate the effects of spatial confinement of photogenerated hot carriers in InGaAs-InAlAs core–shell nanowires, which presents an ideal class of hot carrier solar cell materials due to its suitable electronic properties. Using steady-state photoluminescence spectroscopy, our study reveals that by increasing the degree of spatial confinement and Auger recombination, the effects of hot carriers increase, which is in good agreement with theoretical modeling. However, for thin nanowires, the temperature of hot carriers decreases as the effects of crystal disorder increase. This observation is confirmed by probing the extent of the disorder-induced Urbach tail and linked to the presence of a higher density of stacking defects in the limit of thin nanowires. These findings expand our knowledge of hot carrier thermalization in nanowires, which can be applied for designing efficient 1D hot carrier absorbers for advanced-concept photovoltaic solar cells.
63.
H W Jeong, A Ajay, M Döblinger, S Sturm, M Gómez Ruiz, R Zell, N Mukhundhan, D Stelzner, J Lähnemann, K Müller-Caspary, J J Finley, G Koblmüller
Axial Growth Characteristics of Optically Active InGaAs Nanowire Heterostructures for Integrated Nanophotonic Devices Journal Article
In: ACS Applied Nano Materials, vol. 7, no. 3, pp. 3032-3041, 2024.
@article{nokey,
title = {Axial Growth Characteristics of Optically Active InGaAs Nanowire Heterostructures for Integrated Nanophotonic Devices},
author = {H W Jeong and A Ajay and M D\"{o}blinger and S Sturm and M G\'{o}mez Ruiz and R Zell and N Mukhundhan and D Stelzner and J L\"{a}hnemann and K M\"{u}ller-Caspary and J J Finley and G Koblm\"{u}ller},
url = {https://doi.org/10.1021/acsanm.3c05392},
doi = {10.1021/acsanm.3c05392},
year = {2024},
date = {2024-01-24},
journal = {ACS Applied Nano Materials},
volume = {7},
number = {3},
pages = {3032-3041},
abstract = {III\textendashV semiconductor nanowire (NW) heterostructures with axial InGaAs active regions hold large potential for diverse on-chip device applications, including site-selectively integrated quantum light sources, NW lasers with high material gain, as well as resonant tunneling diodes and avalanche photodiodes. Despite various promising efforts toward high-quality single or multiple axial InGaAs heterostacks using noncatalytic growth mechanisms, the important roles of facet-dependent shape evolution, crystal defects, and the applicability to more universal growth schemes have remained elusive. Here, we report the growth of optically active InGaAs axial NW heterostructures via completely catalyst-free, selective-area molecular beam epitaxy directly on silicon (Si) using GaAs(Sb) NW arrays as tunable, high-uniformity growth templates and highlight fundamental relationships between structural, morphological, and optical properties of the InGaAs region. Structural, compositional, and 3D-tomographic characterizations affirm the desired directional growth along the NW axis with no radial growth observed. Clearly distinct luminescence from the InGaAs active region is demonstrated, where tunable array\textendashgeometry parameters and In content up to 20% are further investigated. Based on the underlying twin-induced growth mode, we further describe the facet-dependent shape and interface evolution of the InGaAs segment and its direct correlation with emission energy.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
III–V semiconductor nanowire (NW) heterostructures with axial InGaAs active regions hold large potential for diverse on-chip device applications, including site-selectively integrated quantum light sources, NW lasers with high material gain, as well as resonant tunneling diodes and avalanche photodiodes. Despite various promising efforts toward high-quality single or multiple axial InGaAs heterostacks using noncatalytic growth mechanisms, the important roles of facet-dependent shape evolution, crystal defects, and the applicability to more universal growth schemes have remained elusive. Here, we report the growth of optically active InGaAs axial NW heterostructures via completely catalyst-free, selective-area molecular beam epitaxy directly on silicon (Si) using GaAs(Sb) NW arrays as tunable, high-uniformity growth templates and highlight fundamental relationships between structural, morphological, and optical properties of the InGaAs region. Structural, compositional, and 3D-tomographic characterizations affirm the desired directional growth along the NW axis with no radial growth observed. Clearly distinct luminescence from the InGaAs active region is demonstrated, where tunable array–geometry parameters and In content up to 20% are further investigated. Based on the underlying twin-induced growth mode, we further describe the facet-dependent shape and interface evolution of the InGaAs segment and its direct correlation with emission energy.
62.
C Qian, M Troue, J Figueiredo, P Soubelet, V Villafañe, J Beierlein, S Klembt, A V Stier, S Höfling, A W Holleitner, J J Finley
Lasing of moiré trapped MoSe2/WSe2 interlayer excitons coupled to a nanocavity Journal Article
In: Science Advances, vol. 10, no. 2, pp. eadk6359, 2024.
@article{nokey,
title = {Lasing of moir\'{e} trapped MoSe2/WSe2 interlayer excitons coupled to a nanocavity},
author = {C Qian and M Troue and J Figueiredo and P Soubelet and V Villafa\~{n}e and J Beierlein and S Klembt and A V Stier and S H\"{o}fling and A W Holleitner and J J Finley},
url = {https://www.science.org/doi/abs/10.1126/sciadv.adk6359},
doi = {doi:10.1126/sciadv.adk6359},
year = {2024},
date = {2024-01-10},
journal = {Science Advances},
volume = {10},
number = {2},
pages = {eadk6359},
abstract = {We report lasing of moir\'{e} trapped interlayer excitons (IXs) by integrating a pristine hBN-encapsulated MoSe2/WSe2 heterobilayer into a high-Q (\>104) nanophotonic cavity. We control the cavity-IX detuning using a magnetic field and measure their dipolar coupling strength to be 78 ± 4 micro\textendashelectron volts, fully consistent with the 82 micro\textendashelectron volts predicted by theory. The emission from the cavity mode shows clear threshold-like behavior as the transition is tuned into resonance with the cavity. We observe a superlinear power dependence accompanied by a narrowing of the linewidth as the distinct features of lasing. The onset and prominence of these threshold-like behaviors are pronounced at resonance while weak off-resonance. Our results show that a lasing transition can be induced in interacting moir\'{e} IXs with macroscopic coherence extending over the length scale of the cavity mode. Such systems raise interesting perspectives for low-power switching and synaptic nanophotonic devices using two-dimensional materials. A 2D material nanocavity laser operating in the regime of discrete localized excitons is achieved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report lasing of moiré trapped interlayer excitons (IXs) by integrating a pristine hBN-encapsulated MoSe2/WSe2 heterobilayer into a high-Q (>104) nanophotonic cavity. We control the cavity-IX detuning using a magnetic field and measure their dipolar coupling strength to be 78 ± 4 micro–electron volts, fully consistent with the 82 micro–electron volts predicted by theory. The emission from the cavity mode shows clear threshold-like behavior as the transition is tuned into resonance with the cavity. We observe a superlinear power dependence accompanied by a narrowing of the linewidth as the distinct features of lasing. The onset and prominence of these threshold-like behaviors are pronounced at resonance while weak off-resonance. Our results show that a lasing transition can be induced in interacting moiré IXs with macroscopic coherence extending over the length scale of the cavity mode. Such systems raise interesting perspectives for low-power switching and synaptic nanophotonic devices using two-dimensional materials. A 2D material nanocavity laser operating in the regime of discrete localized excitons is achieved.
61.
T Schreitmüller, H W Jeong, H Esmaielpour, C E Mead, M Ramsteiner, P Schmiedeke, A Thurn, A Ajay, S Matich, M Döblinger, L J Lauhon, J J Finley, G Koblmüller
Large Tolerance of Lasing Properties to Impurity Defects in GaAs(Sb)-AlGaAs Core-Shell Nanowire Lasers Journal Article
In: Advanced Functional Materials, vol. n/a, no. n/a, pp. 2311210, 2023, ISSN: 1616-301X.
@article{nokey,
title = {Large Tolerance of Lasing Properties to Impurity Defects in GaAs(Sb)-AlGaAs Core-Shell Nanowire Lasers},
author = {T Schreitm\"{u}ller and H W Jeong and H Esmaielpour and C E Mead and M Ramsteiner and P Schmiedeke and A Thurn and A Ajay and S Matich and M D\"{o}blinger and L J Lauhon and J J Finley and G Koblm\"{u}ller},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202311210},
doi = {https://doi.org/10.1002/adfm.202311210},
issn = {1616-301X},
year = {2023},
date = {2023-12-08},
journal = {Advanced Functional Materials},
volume = {n/a},
number = {n/a},
pages = {2311210},
abstract = {Abstract GaAs-AlGaAs based nanowire (NW) lasers hold great potential for on-chip photonic applications, where lasing metrics have steadily improved over the years by optimizing resonator design and surface passivation methods. The factor that will ultimately limit the performance will depend on material properties, such as native- or impurity-induced point defects and their impact on non-radiative recombination. Here, the role of impurity-induced point defects on the lasing performance of low-threshold GaAs(Sb)-AlGaAs NW-lasers is evaluated, particularly by exploring Si-dopants and their associated vacancy complexes. Si-induced point defects and their self-compensating nature are identified using correlated atom probe tomography, resonant Raman scattering, and photoluminescence experiments. Under pulsed optical excitation the lasing threshold is remarkably low (\<10 µJ cm−2) and insensitive to impurity defects over a wide range of Si doping densities, while excess doping ([Si]\>1019 cm−3) imposes increased threshold at low temperature. These characteristics coincide with increased Shockley-Read-Hall recombination, reflected by shorter carrier lifetimes, and reduced internal quantum efficiencies (IQE) . Remarkably, despite the lower IQE the presence of self-compensating Si-vacancy defects provides an improved temperature stability in lasing threshold with higher characteristic temperature and room-temperature lasing. These findings highlight an overall large tolerance of lasing metrics to impurity defects in GaAs-AlGaAs based NW-lasers.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract GaAs-AlGaAs based nanowire (NW) lasers hold great potential for on-chip photonic applications, where lasing metrics have steadily improved over the years by optimizing resonator design and surface passivation methods. The factor that will ultimately limit the performance will depend on material properties, such as native- or impurity-induced point defects and their impact on non-radiative recombination. Here, the role of impurity-induced point defects on the lasing performance of low-threshold GaAs(Sb)-AlGaAs NW-lasers is evaluated, particularly by exploring Si-dopants and their associated vacancy complexes. Si-induced point defects and their self-compensating nature are identified using correlated atom probe tomography, resonant Raman scattering, and photoluminescence experiments. Under pulsed optical excitation the lasing threshold is remarkably low (<10 µJ cm−2) and insensitive to impurity defects over a wide range of Si doping densities, while excess doping ([Si]>1019 cm−3) imposes increased threshold at low temperature. These characteristics coincide with increased Shockley-Read-Hall recombination, reflected by shorter carrier lifetimes, and reduced internal quantum efficiencies (IQE) . Remarkably, despite the lower IQE the presence of self-compensating Si-vacancy defects provides an improved temperature stability in lasing threshold with higher characteristic temperature and room-temperature lasing. These findings highlight an overall large tolerance of lasing metrics to impurity defects in GaAs-AlGaAs based NW-lasers.
60.
A Hötger, W Männer, T Amit, D Hernangómez-Pérez, T Taniguchi, K Watanabe, U Wurstbauer, J J Finley, S Refaely-Abramson, C Kastl, A W Holleitner
Photovoltage and Photocurrent Absorption Spectra of Sulfur Vacancies Locally Patterned in Monolayer MoS2 Journal Article
In: Nano Letters, 2023, ISSN: 1530-6984.
@article{nokey,
title = {Photovoltage and Photocurrent Absorption Spectra of Sulfur Vacancies Locally Patterned in Monolayer MoS2},
author = {A H\"{o}tger and W M\"{a}nner and T Amit and D Hernang\'{o}mez-P\'{e}rez and T Taniguchi and K Watanabe and U Wurstbauer and J J Finley and S Refaely-Abramson and C Kastl and A W Holleitner},
url = {https://doi.org/10.1021/acs.nanolett.3c03517},
doi = {10.1021/acs.nanolett.3c03517},
issn = {1530-6984},
year = {2023},
date = {2023-12-06},
journal = {Nano Letters},
abstract = {We report on the optical absorption characteristics of selectively positioned sulfur vacancies in monolayer MoS2, as observed by photovoltage and photocurrent experiments in an atomistic vertical tunneling circuit at cryogenic and room temperature. Charge carriers are resonantly photoexcited within the defect states before they tunnel through an hBN tunneling barrier to a graphene-based drain contact. Both photovoltage and photocurrent characteristics confirm the optical absorption spectrum as derived from ab initio GW and Bethe\textendashSalpeter equation approximations. Our results reveal the potential of single-vacancy tunneling devices as atomic-scale photodiodes.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report on the optical absorption characteristics of selectively positioned sulfur vacancies in monolayer MoS2, as observed by photovoltage and photocurrent experiments in an atomistic vertical tunneling circuit at cryogenic and room temperature. Charge carriers are resonantly photoexcited within the defect states before they tunnel through an hBN tunneling barrier to a graphene-based drain contact. Both photovoltage and photocurrent characteristics confirm the optical absorption spectrum as derived from ab initio GW and Bethe–Salpeter equation approximations. Our results reveal the potential of single-vacancy tunneling devices as atomic-scale photodiodes.
59.
M Rieger, V Villafane, L M Todenhagen, S Matthies, S Appel, M S Brandt, K Mueller, J J Finley
Fast optoelectronic charge state conversion of silicon vacancies in diamond Journal Article
In: arXiv preprint arXiv:2310.12288, 2023.
@article{nokey,
title = {Fast optoelectronic charge state conversion of silicon vacancies in diamond},
author = {M Rieger and V Villafane and L M Todenhagen and S Matthies and S Appel and M S Brandt and K Mueller and J J Finley},
url = {https://arxiv.org/abs/2310.12288},
doi = {https://doi.org/10.48550/arXiv.2310.12288},
year = {2023},
date = {2023-10-18},
journal = {arXiv preprint arXiv:2310.12288},
abstract = {Group IV vacancy color centers in diamond are promising spin-photon interfaces with strong potential for applications for photonic quantum technologies. Reliable methods for controlling and stabilizing their charge state are urgently needed for scaling to multi-qubit devices. Here, we manipulate the charge state of silicon vacancy (SiV) ensembles by combining luminescence and photo-current spectroscopy. We controllably convert the charge state between the optically active SiV− and dark SiV2− with MHz rates and 90% contrast by judiciously choosing the local potential applied to in-plane surface electrodes and the laser excitation wavelength. We observe intense SiV− photoluminescence under hole-capture, measure the intrinsic conversion time from the dark SiV2− to the bright SiV− to be 36.4(6.7)ms and demonstrate how it can be enhanced by a factor of 105 via optical pumping. Moreover, we obtain new information on the defects that contribute to photo-conductivity, indicating the presence of substitutional nitrogen and divacancies.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Group IV vacancy color centers in diamond are promising spin-photon interfaces with strong potential for applications for photonic quantum technologies. Reliable methods for controlling and stabilizing their charge state are urgently needed for scaling to multi-qubit devices. Here, we manipulate the charge state of silicon vacancy (SiV) ensembles by combining luminescence and photo-current spectroscopy. We controllably convert the charge state between the optically active SiV− and dark SiV2− with MHz rates and 90% contrast by judiciously choosing the local potential applied to in-plane surface electrodes and the laser excitation wavelength. We observe intense SiV− photoluminescence under hole-capture, measure the intrinsic conversion time from the dark SiV2− to the bright SiV− to be 36.4(6.7)ms and demonstrate how it can be enhanced by a factor of 105 via optical pumping. Moreover, we obtain new information on the defects that contribute to photo-conductivity, indicating the presence of substitutional nitrogen and divacancies.
58.
M M Petrić, V Villafañe, P Herrmann, A Ben Mhenni, Y Qin, Y Sayyad, Y Shen, S Tongay, K Müller, G Soavi, J J Finley, M Barbone
Nonlinear Dispersion Relation and Out-of-Plane Second Harmonic Generation in MoSSe and WSSe Janus Monolayers Journal Article
In: Advanced Optical Materials, vol. 11, no. 19, pp. 2300958, 2023, ISSN: 2195-1071.
@article{nokey,
title = {Nonlinear Dispersion Relation and Out-of-Plane Second Harmonic Generation in MoSSe and WSSe Janus Monolayers},
author = {M M Petri\'{c} and V Villafa\~{n}e and P Herrmann and A Ben Mhenni and Y Qin and Y Sayyad and Y Shen and S Tongay and K M\"{u}ller and G Soavi and J J Finley and M Barbone},
url = {https://doi.org/10.1002/adom.202300958},
doi = {https://doi.org/10.1002/adom.202300958},
issn = {2195-1071},
year = {2023},
date = {2023-10-01},
journal = {Advanced Optical Materials},
volume = {11},
number = {19},
pages = {2300958},
abstract = {Abstract Janus transition metal dichalcogenides are an emerging class of atomically thin materials with engineered broken mirror symmetry that gives rise to long-lived dipolar excitons, Rashba splitting, and topologically protected solitons. They hold great promise as a versatile nonlinear optical platform due to their broadband harmonic generation tunability, ease of integration on photonic structures, and nonlinearities beyond the basal crystal plane. Here, second and third harmonic generation in MoSSe and WSSe Janus monolayers is studied. Polarization-resolved spectroscopy is used to map the full second-order susceptibility tensor of MoSSe, including its out-of-plane components. In addition, the effective third-order susceptibility and the second-order nonlinear dispersion close to exciton resonances for both MoSSe and WSSe are measured at room and cryogenic temperatures. This work sets a bedrock for understanding the nonlinear optical properties of Janus transition metal dichalcogenides and probing their use in the next-generation on-chip multifaceted photonic devices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Janus transition metal dichalcogenides are an emerging class of atomically thin materials with engineered broken mirror symmetry that gives rise to long-lived dipolar excitons, Rashba splitting, and topologically protected solitons. They hold great promise as a versatile nonlinear optical platform due to their broadband harmonic generation tunability, ease of integration on photonic structures, and nonlinearities beyond the basal crystal plane. Here, second and third harmonic generation in MoSSe and WSSe Janus monolayers is studied. Polarization-resolved spectroscopy is used to map the full second-order susceptibility tensor of MoSSe, including its out-of-plane components. In addition, the effective third-order susceptibility and the second-order nonlinear dispersion close to exciton resonances for both MoSSe and WSSe are measured at room and cryogenic temperatures. This work sets a bedrock for understanding the nonlinear optical properties of Janus transition metal dichalcogenides and probing their use in the next-generation on-chip multifaceted photonic devices.
57.
R Rizzato, M Schalk, S Mohr, J C Hermann, J P Leibold, F Bruckmaier, G Salvitti, C Qian, P Ji, G V Astakhov, U Kentsch, M Helm, A V Stier, J J Finley, D B Bucher
Extending the coherence of spin defects in hBN enables advanced qubit control and quantum sensing Journal Article
In: Nature Communications, vol. 14, no. 1, pp. 5089, 2023, ISSN: 2041-1723.
@article{nokey,
title = {Extending the coherence of spin defects in hBN enables advanced qubit control and quantum sensing},
author = {R Rizzato and M Schalk and S Mohr and J C Hermann and J P Leibold and F Bruckmaier and G Salvitti and C Qian and P Ji and G V Astakhov and U Kentsch and M Helm and A V Stier and J J Finley and D B Bucher},
url = {https://doi.org/10.1038/s41467-023-40473-w},
doi = {10.1038/s41467-023-40473-w},
issn = {2041-1723},
year = {2023},
date = {2023-08-22},
journal = {Nature Communications},
volume = {14},
number = {1},
pages = {5089},
abstract = {Negatively-charged boron vacancy centers ($$V_B^-$$) in hexagonal Boron Nitride (hBN) are attracting increasing interest since they represent optically-addressable qubits in a van der Waals material. In particular, these spin defects have shown promise as sensors for temperature, pressure, and static magnetic fields. However, their short spin coherence time limits their scope for quantum technology. Here, we apply dynamical decoupling techniques to suppress magnetic noise and extend the spin coherence time by two orders of magnitude, approaching the fundamental T1 relaxation limit. Based on this improvement, we demonstrate advanced spin control and a set of quantum sensing protocols to detect radiofrequency signals with sub-Hz resolution. The corresponding sensitivity is benchmarked against that of state-of-the-art NV-diamond quantum sensors. This work lays the foundation for nanoscale sensing using spin defects in an exfoliable material and opens a promising path to quantum sensors and quantum networks integrated into ultra-thin structures.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Negatively-charged boron vacancy centers ($$V_B^-$$) in hexagonal Boron Nitride (hBN) are attracting increasing interest since they represent optically-addressable qubits in a van der Waals material. In particular, these spin defects have shown promise as sensors for temperature, pressure, and static magnetic fields. However, their short spin coherence time limits their scope for quantum technology. Here, we apply dynamical decoupling techniques to suppress magnetic noise and extend the spin coherence time by two orders of magnitude, approaching the fundamental T1 relaxation limit. Based on this improvement, we demonstrate advanced spin control and a set of quantum sensing protocols to detect radiofrequency signals with sub-Hz resolution. The corresponding sensitivity is benchmarked against that of state-of-the-art NV-diamond quantum sensors. This work lays the foundation for nanoscale sensing using spin defects in an exfoliable material and opens a promising path to quantum sensors and quantum networks integrated into ultra-thin structures.
56.
C Li, A V Scherbakov, P Soubelet, A K Samusev, C Ruppert, N Balakrishnan, V E Gusev, A V Stier, J J Finley, M Bayer, A V Akimov
Coherent Phonons in van der Waals MoSe2/WSe2 Heterobilayers Journal Article
In: Nano Letters, vol. 23, no. 17, pp. 8186-8193, 2023, ISSN: 1530-6984.
@article{nokey,
title = {Coherent Phonons in van der Waals MoSe2/WSe2 Heterobilayers},
author = {C Li and A V Scherbakov and P Soubelet and A K Samusev and C Ruppert and N Balakrishnan and V E Gusev and A V Stier and J J Finley and M Bayer and A V Akimov},
url = {https://doi.org/10.1021/acs.nanolett.3c02316},
doi = {10.1021/acs.nanolett.3c02316},
issn = {1530-6984},
year = {2023},
date = {2023-08-21},
journal = {Nano Letters},
volume = {23},
number = {17},
pages = {8186-8193},
abstract = {The increasing role of two-dimensional (2D) devices requires the development of new techniques for ultrafast control of physical properties in 2D van der Waals (vdW) nanolayers. A special feature of heterobilayers assembled from vdW monolayers is femtosecond separation of photoexcited electrons and holes between the neighboring layers, resulting in the formation of Coulomb force. Using laser pulses, we generate a 0.8 THz coherent breathing mode in MoSe2/WSe2 heterobilayers, which modulates the thickness of the heterobilayer and should modulate the photogenerated electric field in the vdW gap. While the phonon frequency and decay time are independent of the stacking angle between the MoSe2 and WSe2 monolayers, the amplitude decreases at intermediate angles, which is explained by a decrease in the photogenerated electric field between the layers. The modulation of the vdW gap by coherent phonons enables a new technology for the generation of THz radiation in 2D nanodevices with vdW heterobilayers.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The increasing role of two-dimensional (2D) devices requires the development of new techniques for ultrafast control of physical properties in 2D van der Waals (vdW) nanolayers. A special feature of heterobilayers assembled from vdW monolayers is femtosecond separation of photoexcited electrons and holes between the neighboring layers, resulting in the formation of Coulomb force. Using laser pulses, we generate a 0.8 THz coherent breathing mode in MoSe2/WSe2 heterobilayers, which modulates the thickness of the heterobilayer and should modulate the photogenerated electric field in the vdW gap. While the phonon frequency and decay time are independent of the stacking angle between the MoSe2 and WSe2 monolayers, the amplitude decreases at intermediate angles, which is explained by a decrease in the photogenerated electric field between the layers. The modulation of the vdW gap by coherent phonons enables a new technology for the generation of THz radiation in 2D nanodevices with vdW heterobilayers.
55.
T Weber, L Kühner, L Sortino, A Ben Mhenni, N P Wilson, J Kühne, J J Finley, S A Maier, A Tittl
Intrinsic strong light-matter coupling with self-hybridized bound states in the continuum in van der Waals metasurfaces Journal Article
In: Nature Materials, vol. 22, no. 8, pp. 970-976, 2023, ISSN: 1476-4660.
@article{nokey,
title = {Intrinsic strong light-matter coupling with self-hybridized bound states in the continuum in van der Waals metasurfaces},
author = {T Weber and L K\"{u}hner and L Sortino and A Ben Mhenni and N P Wilson and J K\"{u}hne and J J Finley and S A Maier and A Tittl},
url = {https://doi.org/10.1038/s41563-023-01580-7},
doi = {10.1038/s41563-023-01580-7},
issn = {1476-4660},
year = {2023},
date = {2023-06-22},
journal = {Nature Materials},
volume = {22},
number = {8},
pages = {970-976},
abstract = {Photonic bound states in the continuum (BICs) provide a standout platform for strong light-matter coupling with transition metal dichalcogenides (TMDCs) but have so far mostly been implemented as traditional all-dielectric metasurfaces with adjacent TMDC layers, incurring limitations related to strain, mode overlap and material integration. Here, we demonstrate intrinsic strong coupling in BIC-driven metasurfaces composed of nanostructured bulk tungsten disulfide (WS2) and exhibiting resonances with sharp, tailored linewidths and selective enhancement of light-matter interactions. Tuning of the BIC resonances across the exciton resonance in bulk WS2 is achieved by varying the metasurface unit cells, enabling strong coupling with an anticrossing pattern and a Rabi splitting of 116 meV. Crucially, the coupling strength itself can be controlled and is shown to be independent of material-intrinsic losses. Our self-hybridized metasurface platform can readily incorporate other TMDCs or excitonic materials to deliver fundamental insights and practical device concepts for polaritonic applications.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Photonic bound states in the continuum (BICs) provide a standout platform for strong light-matter coupling with transition metal dichalcogenides (TMDCs) but have so far mostly been implemented as traditional all-dielectric metasurfaces with adjacent TMDC layers, incurring limitations related to strain, mode overlap and material integration. Here, we demonstrate intrinsic strong coupling in BIC-driven metasurfaces composed of nanostructured bulk tungsten disulfide (WS2) and exhibiting resonances with sharp, tailored linewidths and selective enhancement of light-matter interactions. Tuning of the BIC resonances across the exciton resonance in bulk WS2 is achieved by varying the metasurface unit cells, enabling strong coupling with an anticrossing pattern and a Rabi splitting of 116 meV. Crucially, the coupling strength itself can be controlled and is shown to be independent of material-intrinsic losses. Our self-hybridized metasurface platform can readily incorporate other TMDCs or excitonic materials to deliver fundamental insights and practical device concepts for polaritonic applications.
54.
T Weber, L Kühner, L Sortino, A Ben Mhenni, N P Wilson, J Kühne, J J Finley, S A Maier, A Tittl
Intrinsic strong light-matter coupling with self-hybridized bound states in the continuum in van der Waals metasurfaces Journal Article
In: Nature Materials, vol. 22, no. 8, pp. 970-976, 2023, ISSN: 1476-4660.
@article{nokey,
title = {Intrinsic strong light-matter coupling with self-hybridized bound states in the continuum in van der Waals metasurfaces},
author = {T Weber and L K\"{u}hner and L Sortino and A Ben Mhenni and N P Wilson and J K\"{u}hne and J J Finley and S A Maier and A Tittl},
url = {https://doi.org/10.1038/s41563-023-01580-7},
doi = {10.1038/s41563-023-01580-7},
issn = {1476-4660},
year = {2023},
date = {2023-06-22},
journal = {Nature Materials},
volume = {22},
number = {8},
pages = {970-976},
abstract = {Photonic bound states in the continuum (BICs) provide a standout platform for strong light-matter coupling with transition metal dichalcogenides (TMDCs) but have so far mostly been implemented as traditional all-dielectric metasurfaces with adjacent TMDC layers, incurring limitations related to strain, mode overlap and material integration. Here, we demonstrate intrinsic strong coupling in BIC-driven metasurfaces composed of nanostructured bulk tungsten disulfide (WS2) and exhibiting resonances with sharp, tailored linewidths and selective enhancement of light-matter interactions. Tuning of the BIC resonances across the exciton resonance in bulk WS2 is achieved by varying the metasurface unit cells, enabling strong coupling with an anticrossing pattern and a Rabi splitting of 116 meV. Crucially, the coupling strength itself can be controlled and is shown to be independent of material-intrinsic losses. Our self-hybridized metasurface platform can readily incorporate other TMDCs or excitonic materials to deliver fundamental insights and practical device concepts for polaritonic applications.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Photonic bound states in the continuum (BICs) provide a standout platform for strong light-matter coupling with transition metal dichalcogenides (TMDCs) but have so far mostly been implemented as traditional all-dielectric metasurfaces with adjacent TMDC layers, incurring limitations related to strain, mode overlap and material integration. Here, we demonstrate intrinsic strong coupling in BIC-driven metasurfaces composed of nanostructured bulk tungsten disulfide (WS2) and exhibiting resonances with sharp, tailored linewidths and selective enhancement of light-matter interactions. Tuning of the BIC resonances across the exciton resonance in bulk WS2 is achieved by varying the metasurface unit cells, enabling strong coupling with an anticrossing pattern and a Rabi splitting of 116 meV. Crucially, the coupling strength itself can be controlled and is shown to be independent of material-intrinsic losses. Our self-hybridized metasurface platform can readily incorporate other TMDCs or excitonic materials to deliver fundamental insights and practical device concepts for polaritonic applications.
53.
A Henning, S Levashov, C Qian, T Grünleitner, J Primbs, J J Finley, I D Sharp
Tunable Encapsulation and Doping of Monolayer MoS2 by In Situ Probing of Excitonic Properties During Atomic Layer Deposition Journal Article
In: Advanced Materials Interfaces, vol. 10, no. 15, pp. 2202429, 2023, ISSN: 2196-7350.
@article{nokey,
title = {Tunable Encapsulation and Doping of Monolayer MoS2 by In Situ Probing of Excitonic Properties During Atomic Layer Deposition},
author = {A Henning and S Levashov and C Qian and T Gr\"{u}nleitner and J Primbs and J J Finley and I D Sharp},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/admi.202202429},
doi = {https://doi.org/10.1002/admi.202202429},
issn = {2196-7350},
year = {2023},
date = {2023-04-18},
journal = {Advanced Materials Interfaces},
volume = {10},
number = {15},
pages = {2202429},
abstract = {Abstract Here, it is shown that in situ spectroscopic ellipsometry (SE) is a powerful method for probing the effects of reactant adsorption and film formation on the excitonic properties of 2D materials during atomic layer deposition (ALD), thus allowing optimization of both film growth and opto(electronic) characteristics in real time. Facilitated by in situ SE during ALD on monolayer MoS2, a low temperature (40 °C) process for encapsulation of the 2D material with a nanometer-thin alumina (AlOx) layer is investigated, which results in a 2D/3D interface governed by van der Waals interactions rather than chemical bonding. Charge transfer doping of MoS2 by AlOx is found to be an interfacial phenomenon that initiates from the earliest stages of film formation, but saturates upon deposition of a closed layer. However, the lack of chemical binding interactions at the 2D/3D interface enables physical removal of the AlOx that results in a reversal of the charge transfer doping effect. Overall, it is demonstrated that in situ SE of 2D materials during ALD can precisely probe the impact of film formation on sensitive optoelectronic characteristics of 2D materials, which is of key importance in the development of integrated 2D/3D systems.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Here, it is shown that in situ spectroscopic ellipsometry (SE) is a powerful method for probing the effects of reactant adsorption and film formation on the excitonic properties of 2D materials during atomic layer deposition (ALD), thus allowing optimization of both film growth and opto(electronic) characteristics in real time. Facilitated by in situ SE during ALD on monolayer MoS2, a low temperature (40 °C) process for encapsulation of the 2D material with a nanometer-thin alumina (AlOx) layer is investigated, which results in a 2D/3D interface governed by van der Waals interactions rather than chemical bonding. Charge transfer doping of MoS2 by AlOx is found to be an interfacial phenomenon that initiates from the earliest stages of film formation, but saturates upon deposition of a closed layer. However, the lack of chemical binding interactions at the 2D/3D interface enables physical removal of the AlOx that results in a reversal of the charge transfer doping effect. Overall, it is demonstrated that in situ SE of 2D materials during ALD can precisely probe the impact of film formation on sensitive optoelectronic characteristics of 2D materials, which is of key importance in the development of integrated 2D/3D systems.
52.
M Kögl, P Soubelet, M Brotons-Gisbert, A V Stier, B D Gerardot, J J Finley
Moiré straintronics: a universal platform for reconfigurable quantum materials Journal Article
In: npj 2D Materials and Applications, vol. 7, no. 1, pp. 32, 2023, ISSN: 2397-7132.
@article{nokey,
title = {Moir\'{e} straintronics: a universal platform for reconfigurable quantum materials},
author = {M K\"{o}gl and P Soubelet and M Brotons-Gisbert and A V Stier and B D Gerardot and J J Finley},
url = {https://doi.org/10.1038/s41699-023-00382-4},
doi = {10.1038/s41699-023-00382-4},
issn = {2397-7132},
year = {2023},
date = {2023-04-18},
journal = {npj 2D Materials and Applications},
volume = {7},
number = {1},
pages = {32},
abstract = {Large-scale two-dimensional (2D) moir\'{e} superlattices are driving a revolution in designer quantum materials. The electronic interactions in these superlattices, strongly dependent on the periodicity and symmetry of the moir\'{e} pattern, critically determine the emergent properties and phase diagrams. To date, the relative twist angle between two layers has been the primary tuning parameter for a given choice of constituent crystals. Here, we establish strain as a powerful mechanism to in situ modify the moir\'{e} periodicity and symmetry. We develop an analytically exact mathematical description for the moir\'{e} lattice under arbitrary in-plane heterostrain acting on any bilayer structure. We demonstrate the ability to fine-tune the moir\'{e} lattice near critical points, such as the magic angle in bilayer graphene, or fully reconfigure the moir\'{e} lattice symmetry beyond that imposed by the unstrained constituent crystals. Due to this unprecedented simultaneous control over the strength of electronic interactions and lattice symmetry, 2D heterostrain provides a powerful platform to engineer, tune, and probe strongly correlated moir\'{e} materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Large-scale two-dimensional (2D) moiré superlattices are driving a revolution in designer quantum materials. The electronic interactions in these superlattices, strongly dependent on the periodicity and symmetry of the moiré pattern, critically determine the emergent properties and phase diagrams. To date, the relative twist angle between two layers has been the primary tuning parameter for a given choice of constituent crystals. Here, we establish strain as a powerful mechanism to in situ modify the moiré periodicity and symmetry. We develop an analytically exact mathematical description for the moiré lattice under arbitrary in-plane heterostrain acting on any bilayer structure. We demonstrate the ability to fine-tune the moiré lattice near critical points, such as the magic angle in bilayer graphene, or fully reconfigure the moiré lattice symmetry beyond that imposed by the unstrained constituent crystals. Due to this unprecedented simultaneous control over the strength of electronic interactions and lattice symmetry, 2D heterostrain provides a powerful platform to engineer, tune, and probe strongly correlated moiré materials.
51.
A Hötger, T Amit, J Klein, K Barthelmi, T Pelini, A Delhomme, S Rey, M Potemski, C Faugeras, G Cohen, D Hernangómez-Pérez, T Taniguchi, K Watanabe, C Kastl, J J Finley, S Refaely-Abramson, A W Holleitner, A V Stier
Spin-defect characteristics of single sulfur vacancies in monolayer MoS2 Journal Article
In: npj 2D Materials and Applications, vol. 7, no. 1, pp. 30, 2023, ISSN: 2397-7132.
@article{nokey,
title = {Spin-defect characteristics of single sulfur vacancies in monolayer MoS2},
author = {A H\"{o}tger and T Amit and J Klein and K Barthelmi and T Pelini and A Delhomme and S Rey and M Potemski and C Faugeras and G Cohen and D Hernang\'{o}mez-P\'{e}rez and T Taniguchi and K Watanabe and C Kastl and J J Finley and S Refaely-Abramson and A W Holleitner and A V Stier},
url = {https://doi.org/10.1038/s41699-023-00392-2},
doi = {10.1038/s41699-023-00392-2},
issn = {2397-7132},
year = {2023},
date = {2023-04-08},
journal = {npj 2D Materials and Applications},
volume = {7},
number = {1},
pages = {30},
abstract = {Single spin-defects in 2D transition-metal dichalcogenides are natural spin-photon interfaces for quantum applications. Here we report high-field magneto-photoluminescence spectroscopy from three emission lines (Q1, Q2, and Q*) of He-ion induced sulfur vacancies in monolayer MoS2. Analysis of the asymmetric PL lineshapes in combination with the diamagnetic shift of Q1 and Q2 yields a consistent picture of localized emitters with a wave function extent of ~3.5 nm. The distinct valley-Zeeman splitting in out-of-plane B-fields and the brightening of dark states through in-plane B-fields necessitates spin-valley selectivity of the defect states and lifted spin-degeneracy at zero field. Comparing our results to ab initio calculations identifies the nature of Q1 and Q2 and suggests that Q* is the emission from a chemically functionalized defect. Analysis of the optical degree of circular polarization reveals that the Fermi level is a parameter that enables the tunability of the emitter. These results show that defects in 2D semiconductors may be utilized for quantum technologies.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Single spin-defects in 2D transition-metal dichalcogenides are natural spin-photon interfaces for quantum applications. Here we report high-field magneto-photoluminescence spectroscopy from three emission lines (Q1, Q2, and Q*) of He-ion induced sulfur vacancies in monolayer MoS2. Analysis of the asymmetric PL lineshapes in combination with the diamagnetic shift of Q1 and Q2 yields a consistent picture of localized emitters with a wave function extent of ~3.5 nm. The distinct valley-Zeeman splitting in out-of-plane B-fields and the brightening of dark states through in-plane B-fields necessitates spin-valley selectivity of the defect states and lifted spin-degeneracy at zero field. Comparing our results to ab initio calculations identifies the nature of Q1 and Q2 and suggests that Q* is the emission from a chemically functionalized defect. Analysis of the optical degree of circular polarization reveals that the Fermi level is a parameter that enables the tunability of the emitter. These results show that defects in 2D semiconductors may be utilized for quantum technologies.
50.
C Qian, V Villafañe, M M Petrić, P Soubelet, A V Stier, J J Finley
Coupling of $mathrmMoS_2$ Excitons with Lattice Phonons and Cavity Vibrational Phonons in Hybrid Nanobeam Cavities Journal Article
In: Physical Review Letters, vol. 130, no. 12, pp. 126901, 2023.
@article{nokey,
title = {Coupling of $mathrmMoS_2$ Excitons with Lattice Phonons and Cavity Vibrational Phonons in Hybrid Nanobeam Cavities},
author = {C Qian and V Villafa\~{n}e and M M Petri\'{c} and P Soubelet and A V Stier and J J Finley},
url = {https://link.aps.org/doi/10.1103/PhysRevLett.130.126901},
doi = {10.1103/PhysRevLett.130.126901},
year = {2023},
date = {2023-03-23},
journal = {Physical Review Letters},
volume = {130},
number = {12},
pages = {126901},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
49.
V Villafañe, M Kremser, R Hübner, M M Petrić, N P Wilson, A V Stier, K Müller, M Florian, A Steinhoff, J J Finley
Twist-Dependent Intra- and Interlayer Excitons in Moiré $mathrmMoSe_2$ Homobilayers Journal Article
In: Physical Review Letters, vol. 130, no. 2, pp. 026901, 2023.
@article{nokey,
title = {Twist-Dependent Intra- and Interlayer Excitons in Moir\'{e} $mathrmMoSe_2$ Homobilayers},
author = {V Villafa\~{n}e and M Kremser and R H\"{u}bner and M M Petri\'{c} and N P Wilson and A V Stier and K M\"{u}ller and M Florian and A Steinhoff and J J Finley},
url = {https://link.aps.org/doi/10.1103/PhysRevLett.130.026901},
doi = {10.1103/PhysRevLett.130.026901},
year = {2023},
date = {2023-01-11},
journal = {Physical Review Letters},
volume = {130},
number = {2},
pages = {026901},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
48.
A Bechtold, T Simmet, F Sbrezny, N A Sinitsyn, K Müller, J J Finley
Relaxation of Electron and Hole Spin Qubits in III–V Quantum Dots Book Chapter
In: Photonic Quantum Technologies, pp. 377-431, 2023.
@inbook{nokey,
title = {Relaxation of Electron and Hole Spin Qubits in III\textendashV Quantum Dots},
author = {A Bechtold and T Simmet and F Sbrezny and N A Sinitsyn and K M\"{u}ller and J J Finley},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/9783527837427.ch16},
doi = {https://doi.org/10.1002/9783527837427.ch16},
year = {2023},
date = {2023-01-01},
booktitle = {Photonic Quantum Technologies},
pages = {377-431},
abstract = {Summary The control of solid-state qubits for quantum information processing requires a detailed understanding of the mechanisms responsible for decoherence. During the past decade, considerable progress has been achieved for describing the qubit dynamics in relatively strong external magnetic fields. However, testing theoretical predictions at very low magnetic fields has proven difficult in optically active dots. Here, we describe our studies of electron and hole spin qubit dephasing in single InGaAs quantum dots using spin memory devices. The results show that without applied magnetic fields, the initially orientated electron spin rapidly loses its polarization due to precession around the fluctuating Overhauser field with an effective magnetic field amplitude of 10.5 mT. The inhomogeneous dephasing time associated with these hyperfine mediated dynamics is T 2 * ∼ 2 ns. Over longer timescales, an unexpected stage of central spin relaxation is observed, namely the appearance of a second feature in the relaxation curve around T Q = 750 ns arising from quadrupolar coupling. In comparison, hole spin qubits are shown couple significantly more weakly to the nuclear spin bath. We measure a ∼ 100 × times longer dephasing time T 2 * ∼ 210 ns for hole spin qubits compared with the electron spin. We also obtain evidence for the impact of anisotropic hyperfine coupling on the spin polarization decay, allowing us to quantify the degree of anisotropy α = 0.19 which is fundamental to the character of the confined hole spin wave function. By modeling this behavior, we derive the degree of light-hole heavy-hole mixing, which is an essential mechanism for enabling hole spin dephasing and thus refining the description of hole hyperfine coupling beyond the initially suggested pure Ising form.},
keywords = {},
pubstate = {published},
tppubtype = {inbook}
}
Summary The control of solid-state qubits for quantum information processing requires a detailed understanding of the mechanisms responsible for decoherence. During the past decade, considerable progress has been achieved for describing the qubit dynamics in relatively strong external magnetic fields. However, testing theoretical predictions at very low magnetic fields has proven difficult in optically active dots. Here, we describe our studies of electron and hole spin qubit dephasing in single InGaAs quantum dots using spin memory devices. The results show that without applied magnetic fields, the initially orientated electron spin rapidly loses its polarization due to precession around the fluctuating Overhauser field with an effective magnetic field amplitude of 10.5 mT. The inhomogeneous dephasing time associated with these hyperfine mediated dynamics is T 2 * ∼ 2 ns. Over longer timescales, an unexpected stage of central spin relaxation is observed, namely the appearance of a second feature in the relaxation curve around T Q = 750 ns arising from quadrupolar coupling. In comparison, hole spin qubits are shown couple significantly more weakly to the nuclear spin bath. We measure a ∼ 100 × times longer dephasing time T 2 * ∼ 210 ns for hole spin qubits compared with the electron spin. We also obtain evidence for the impact of anisotropic hyperfine coupling on the spin polarization decay, allowing us to quantify the degree of anisotropy α = 0.19 which is fundamental to the character of the confined hole spin wave function. By modeling this behavior, we derive the degree of light-hole heavy-hole mixing, which is an essential mechanism for enabling hole spin dephasing and thus refining the description of hole hyperfine coupling beyond the initially suggested pure Ising form.
47.
P Ji, C Qian, J J Finley, S Yang
Thickness Insensitive Nanocavities for 2D Heterostructures using Photonic Molecules Book
2023.
@book{nokey,
title = {Thickness Insensitive Nanocavities for 2D Heterostructures using Photonic Molecules},
author = {P Ji and C Qian and J J Finley and S Yang},
doi = {10.48550/arXiv.2305.20034},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
abstract = {Two-dimensional (2D) heterostructures integrated into nanophotonic cavities have emerged as a promising approach towards novel photonic and opto-electronic devices. However, the thickness of the 2D heterostructure has a strong influence on the resonance frequency of the nanocavity. For a single cavity, the resonance frequency shifts approximately linearly with the thickness. Here, we propose to use the inherent non-linearity of the mode coupling to render the cavity mode insensitive to the thickness of the 2D heterostructure. Based on the couple mode theory, we reveal that this goal can be achieved using either a homoatomic molecule with a filtered coupling or heteroatomic molecules. We perform numerical simulations to further demonstrate the robustness of the eigenfrequency in the proposed photonic molecules. Our results render nanophotonic structures insensitive to the thickness of 2D materials, thus owing appealing potential in energy- or detuning-sensitive applications such as cavity quantum electrodynamics.},
keywords = {},
pubstate = {published},
tppubtype = {book}
}
Two-dimensional (2D) heterostructures integrated into nanophotonic cavities have emerged as a promising approach towards novel photonic and opto-electronic devices. However, the thickness of the 2D heterostructure has a strong influence on the resonance frequency of the nanocavity. For a single cavity, the resonance frequency shifts approximately linearly with the thickness. Here, we propose to use the inherent non-linearity of the mode coupling to render the cavity mode insensitive to the thickness of the 2D heterostructure. Based on the couple mode theory, we reveal that this goal can be achieved using either a homoatomic molecule with a filtered coupling or heteroatomic molecules. We perform numerical simulations to further demonstrate the robustness of the eigenfrequency in the proposed photonic molecules. Our results render nanophotonic structures insensitive to the thickness of 2D materials, thus owing appealing potential in energy- or detuning-sensitive applications such as cavity quantum electrodynamics.
46.
M O Hill, P Schmiedeke, C Huang, S Maddali, X Hu, S O Hruszkewycz, J J Finley, G Koblmüller, L J Lauhon
3D Bragg Coherent Diffraction Imaging of Extended Nanowires: Defect Formation in Highly Strained InGaAs Quantum Wells Journal Article
In: ACS Nano, vol. 16, no. 12, pp. 20281-20293, 2022, ISSN: 1936-0851.
@article{nokey,
title = {3D Bragg Coherent Diffraction Imaging of Extended Nanowires: Defect Formation in Highly Strained InGaAs Quantum Wells},
author = {M O Hill and P Schmiedeke and C Huang and S Maddali and X Hu and S O Hruszkewycz and J J Finley and G Koblm\"{u}ller and L J Lauhon},
url = {https://doi.org/10.1021/acsnano.2c06071},
doi = {10.1021/acsnano.2c06071},
issn = {1936-0851},
year = {2022},
date = {2022-12-27},
journal = {ACS Nano},
volume = {16},
number = {12},
pages = {20281-20293},
abstract = {InGaAs quantum wells embedded in GaAs nanowires can serve as compact near-infrared emitters for direct integration onto Si complementary metal oxide semiconductor technology. While the core\textendashshell geometry in principle allows for a greater tuning of composition and emission, especially farther into the infrared, the practical limits of elastic strain accommodation in quantum wells on multifaceted nanowires have not been established. One barrier to progress is the difficulty of directly comparing the emission characteristics and the precise microstructure of a single nanowire. Here we report an approach to correlating quantum well morphology, strain, defects, and emission to understand the limits of elastic strain accommodation in nanowire quantum wells specific to their geometry. We realize full 3D Bragg coherent diffraction imaging (BCDI) of intact quantum wells on vertically oriented epitaxial nanowires, which enables direct correlation with single-nanowire photoluminescence. By growing In0.2Ga0.8As quantum wells of distinct thicknesses on different facets of the same nanowire, we identified the critical thickness at which defects are nucleated. A correlation with a traditional transmission electron microscopy analysis confirms that BCDI can image the extended structure of defects. Finite element simulations of electron and hole states explain the emission characteristics arising from strained and partially relaxed regions. This approach, imaging the 3D strain and microstructure of intact nanowire core\textendashshell structures with application-relevant dimensions, can aid the development of predictive models that enable the design of new compact infrared emitters.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
InGaAs quantum wells embedded in GaAs nanowires can serve as compact near-infrared emitters for direct integration onto Si complementary metal oxide semiconductor technology. While the core–shell geometry in principle allows for a greater tuning of composition and emission, especially farther into the infrared, the practical limits of elastic strain accommodation in quantum wells on multifaceted nanowires have not been established. One barrier to progress is the difficulty of directly comparing the emission characteristics and the precise microstructure of a single nanowire. Here we report an approach to correlating quantum well morphology, strain, defects, and emission to understand the limits of elastic strain accommodation in nanowire quantum wells specific to their geometry. We realize full 3D Bragg coherent diffraction imaging (BCDI) of intact quantum wells on vertically oriented epitaxial nanowires, which enables direct correlation with single-nanowire photoluminescence. By growing In0.2Ga0.8As quantum wells of distinct thicknesses on different facets of the same nanowire, we identified the critical thickness at which defects are nucleated. A correlation with a traditional transmission electron microscopy analysis confirms that BCDI can image the extended structure of defects. Finite element simulations of electron and hole states explain the emission characteristics arising from strained and partially relaxed regions. This approach, imaging the 3D strain and microstructure of intact nanowire core–shell structures with application-relevant dimensions, can aid the development of predictive models that enable the design of new compact infrared emitters.
45.
A Henning, J D Bartl, L Wolz, M Christis, F Rauh, M Bissolo, T Grünleitner, J Eichhorn, P Zeller, M Amati, L Gregoratti, J J Finley, B Rieger, M Stutzmann, I D Sharp
Spatially-Modulated Silicon Interface Energetics Via Hydrogen Plasma-Assisted Atomic Layer Deposition of Ultrathin Alumina Journal Article
In: Advanced Materials Interfaces, vol. 10, iss. 6, pp. 2202166, 2022, ISSN: 2196-7350.
@article{nokey,
title = {Spatially-Modulated Silicon Interface Energetics Via Hydrogen Plasma-Assisted Atomic Layer Deposition of Ultrathin Alumina},
author = {A Henning and J D Bartl and L Wolz and M Christis and F Rauh and M Bissolo and T Gr\"{u}nleitner and J Eichhorn and P Zeller and M Amati and L Gregoratti and J J Finley and B Rieger and M Stutzmann and I D Sharp},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/admi.202202166},
doi = {https://doi.org/10.1002/admi.202202166},
issn = {2196-7350},
year = {2022},
date = {2022-12-16},
urldate = {2022-12-16},
journal = {Advanced Materials Interfaces},
volume = {10},
issue = {6},
pages = {2202166},
abstract = {Abstract Atomic layer deposition (ALD) is a key technique for the continued scaling of semiconductor devices, which increasingly relies on scalable processes for interface manipulation of structured surfaces on the atomic level. While ALD allows the synthesis of conformal films with utmost control over the thickness, atomically-defined closed coatings and surface modifications are challenging to achieve because of 3D growth during nucleation. Here, a route is presented toward the sub-nanometer thin and continuous aluminum oxide (AlOx) coatings on silicon substrates for the spatial control of the surface charge density and interface energetics. Trimethylaluminum in combination with remote hydrogen plasma is used instead of a gas-phase oxidant for the transformation of silicon dioxide (SiO2) into alumina. Depending on the number of ALD cycles, the SiO2 can be partially or fully transformed, which is exploited to deposit ultrathin AlOx layers in selected regions defined by lithographic patterning. The resulting patterned surfaces are characterized by lateral AlOx/SiO2 interfaces possessing 0.3 nm step heights and surface potential steps exceeding 0.4 V. In addition, the introduction of fixed negative charges of 9 × 1012 cm−2 enables modulation of the surface band bending, which is relevant to the field-effect passivation of silicon and low-impedance charge transfer across contact interfaces.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Atomic layer deposition (ALD) is a key technique for the continued scaling of semiconductor devices, which increasingly relies on scalable processes for interface manipulation of structured surfaces on the atomic level. While ALD allows the synthesis of conformal films with utmost control over the thickness, atomically-defined closed coatings and surface modifications are challenging to achieve because of 3D growth during nucleation. Here, a route is presented toward the sub-nanometer thin and continuous aluminum oxide (AlOx) coatings on silicon substrates for the spatial control of the surface charge density and interface energetics. Trimethylaluminum in combination with remote hydrogen plasma is used instead of a gas-phase oxidant for the transformation of silicon dioxide (SiO2) into alumina. Depending on the number of ALD cycles, the SiO2 can be partially or fully transformed, which is exploited to deposit ultrathin AlOx layers in selected regions defined by lithographic patterning. The resulting patterned surfaces are characterized by lateral AlOx/SiO2 interfaces possessing 0.3 nm step heights and surface potential steps exceeding 0.4 V. In addition, the introduction of fixed negative charges of 9 × 1012 cm−2 enables modulation of the surface band bending, which is relevant to the field-effect passivation of silicon and low-impedance charge transfer across contact interfaces.
44.
T Grünleitner, A Henning, M Bissolo, M Zengerle, L Gregoratti, M Amati, P Zeller, J Eichhorn, A V Stier, A W Holleitner, J J Finley, I D Sharp
In: ACS Nano, 2022, ISSN: 1936-0851.
@article{nokey,
title = {Real-Time Investigation of Sulfur Vacancy Generation and Passivation in Monolayer Molybdenum Disulfide via in situ X-ray Photoelectron Spectromicroscopy},
author = {T Gr\"{u}nleitner and A Henning and M Bissolo and M Zengerle and L Gregoratti and M Amati and P Zeller and J Eichhorn and A V Stier and A W Holleitner and J J Finley and I D Sharp},
url = {https://doi.org/10.1021/acsnano.2c06317},
doi = {10.1021/acsnano.2c06317},
issn = {1936-0851},
year = {2022},
date = {2022-12-14},
journal = {ACS Nano},
abstract = {Understanding the chemical and electronic properties of point defects in two-dimensional materials, as well as their generation and passivation, is essential for the development of functional systems, spanning from next-generation optoelectronic devices to advanced catalysis. Here, we use synchrotron-based X-ray photoelectron spectroscopy (XPS) with submicron spatial resolution to create sulfur vacancies (SVs) in monolayer MoS2 and monitor their chemical and electronic properties in situ during the defect creation process. X-ray irradiation leads to the emergence of a distinct Mo 3d spectral feature associated with undercoordinated Mo atoms. Real-time analysis of the evolution of this feature, along with the decrease of S content, reveals predominant monosulfur vacancy generation at low doses and preferential disulfur vacancy generation at high doses. Formation of these defects leads to a shift of the Fermi level toward the valence band (VB) edge, introduction of electronic states within the VB, and formation of lateral pn junctions. These findings are consistent with theoretical predictions that SVs serve as deep acceptors and are not responsible for the ubiquitous n-type conductivity of MoS2. In addition, we find that these defects are metastable upon short-term exposure to ambient air. By contrast, in situ oxygen exposure during XPS measurements enables passivation of SVs, resulting in partial elimination of undercoordinated Mo sites and reduction of SV-related states near the VB edge. Correlative Raman spectroscopy and photoluminescence measurements confirm our findings of localized SV generation and passivation, thereby demonstrating the connection between chemical, structural, and optoelectronic properties of SVs in MoS2.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Understanding the chemical and electronic properties of point defects in two-dimensional materials, as well as their generation and passivation, is essential for the development of functional systems, spanning from next-generation optoelectronic devices to advanced catalysis. Here, we use synchrotron-based X-ray photoelectron spectroscopy (XPS) with submicron spatial resolution to create sulfur vacancies (SVs) in monolayer MoS2 and monitor their chemical and electronic properties in situ during the defect creation process. X-ray irradiation leads to the emergence of a distinct Mo 3d spectral feature associated with undercoordinated Mo atoms. Real-time analysis of the evolution of this feature, along with the decrease of S content, reveals predominant monosulfur vacancy generation at low doses and preferential disulfur vacancy generation at high doses. Formation of these defects leads to a shift of the Fermi level toward the valence band (VB) edge, introduction of electronic states within the VB, and formation of lateral pn junctions. These findings are consistent with theoretical predictions that SVs serve as deep acceptors and are not responsible for the ubiquitous n-type conductivity of MoS2. In addition, we find that these defects are metastable upon short-term exposure to ambient air. By contrast, in situ oxygen exposure during XPS measurements enables passivation of SVs, resulting in partial elimination of undercoordinated Mo sites and reduction of SV-related states near the VB edge. Correlative Raman spectroscopy and photoluminescence measurements confirm our findings of localized SV generation and passivation, thereby demonstrating the connection between chemical, structural, and optoelectronic properties of SVs in MoS2.
43.
A Micevic, N Pettinger, A Hötger, L Sigl, M Florian, T Taniguchi, K Watanabe, K Müller, J J Finley, C Kastl, A W Holleitner
On-demand generation of optically active defects in monolayer WS2 by a focused helium ion beam Journal Article
In: Applied Physics Letters, vol. 121, no. 18, pp. 183101, 2022, ISSN: 0003-6951.
@article{nokey,
title = {On-demand generation of optically active defects in monolayer WS2 by a focused helium ion beam},
author = {A Micevic and N Pettinger and A H\"{o}tger and L Sigl and M Florian and T Taniguchi and K Watanabe and K M\"{u}ller and J J Finley and C Kastl and A W Holleitner},
url = {https://doi.org/10.1063/5.0118697},
doi = {10.1063/5.0118697},
issn = {0003-6951},
year = {2022},
date = {2022-10-31},
journal = {Applied Physics Letters},
volume = {121},
number = {18},
pages = {183101},
abstract = {We demonstrate that optically active emitters can be locally generated by focusing a He-ion beam onto monolayer WS2 encapsulated in hBN. The emitters show a low-temperature photoluminescence spectrum, which is well described by an independent Boson model for localized emitters. Consistently, the photoluminescence intensity of the emitters saturates at low excitation intensities, which is distinct to the photoluminescence of excitonic transitions in the investigated WS2 monolayers. The demonstrated method allows us to position defect emitters in WS2 monolayers on demand. A statistical analysis suggests the generation yield of individual emitters to be as high as 11% at the highest investigated He-ion doses.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We demonstrate that optically active emitters can be locally generated by focusing a He-ion beam onto monolayer WS2 encapsulated in hBN. The emitters show a low-temperature photoluminescence spectrum, which is well described by an independent Boson model for localized emitters. Consistently, the photoluminescence intensity of the emitters saturates at low excitation intensities, which is distinct to the photoluminescence of excitonic transitions in the investigated WS2 monolayers. The demonstrated method allows us to position defect emitters in WS2 monolayers on demand. A statistical analysis suggests the generation yield of individual emitters to be as high as 11% at the highest investigated He-ion doses.
42.
F Sigger, I Amersdorffer, A Hötger, M Nutz, J Kiemle, T Taniguchi, K Watanabe, M Förg, J Noe, J J Finley, A Högele, A W Holleitner, T Hümmer, D Hunger, C Kastl
Ultra-Sensitive Extinction Measurements of Optically Active Defects in Monolayer MoS2 Journal Article
In: The Journal of Physical Chemistry Letters, pp. 10291-10296, 2022.
@article{nokey,
title = {Ultra-Sensitive Extinction Measurements of Optically Active Defects in Monolayer MoS2},
author = {F Sigger and I Amersdorffer and A H\"{o}tger and M Nutz and J Kiemle and T Taniguchi and K Watanabe and M F\"{o}rg and J Noe and J J Finley and A H\"{o}gele and A W Holleitner and T H\"{u}mmer and D Hunger and C Kastl},
url = {https://doi.org/10.1021/acs.jpclett.2c02386},
doi = {10.1021/acs.jpclett.2c02386},
year = {2022},
date = {2022-10-28},
journal = {The Journal of Physical Chemistry Letters},
pages = {10291-10296},
abstract = {We utilize cavity-enhanced extinction spectroscopy to directly quantify the optical absorption of defects in MoS2 generated by helium ion bombardment. We achieve hyperspectral imaging of specific defect patterns with a detection limit below 0.01% extinction, corresponding to a detectable defect density below 1 × 1011 cm\textendash2. The corresponding spectra reveal a broad subgap absorption, being consistent with theoretical predictions related to sulfur vacancy-bound excitons in MoS2. Our results highlight cavity-enhanced extinction spectroscopy as efficient means for the detection of optical transitions in nanoscale thin films with weak absorption, applicable to a broad range of materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We utilize cavity-enhanced extinction spectroscopy to directly quantify the optical absorption of defects in MoS2 generated by helium ion bombardment. We achieve hyperspectral imaging of specific defect patterns with a detection limit below 0.01% extinction, corresponding to a detectable defect density below 1 × 1011 cm–2. The corresponding spectra reveal a broad subgap absorption, being consistent with theoretical predictions related to sulfur vacancy-bound excitons in MoS2. Our results highlight cavity-enhanced extinction spectroscopy as efficient means for the detection of optical transitions in nanoscale thin films with weak absorption, applicable to a broad range of materials.
41.
D Ruhstorfer, M Döblinger, H Riedl, J J Finley, G Koblmüller
Role of twin defects on growth dynamics and size distribution of undoped and Si-doped GaAs nanowires by selective area epitaxy Journal Article
In: Journal of Applied Physics, vol. 132, no. 20, pp. 204302, 2022.
@article{nokey,
title = {Role of twin defects on growth dynamics and size distribution of undoped and Si-doped GaAs nanowires by selective area epitaxy},
author = {D Ruhstorfer and M D\"{o}blinger and H Riedl and J J Finley and G Koblm\"{u}ller},
url = {https://aip.scitation.org/doi/abs/10.1063/5.0124808},
doi = {10.1063/5.0124808},
year = {2022},
date = {2022-09-08},
journal = {Journal of Applied Physics},
volume = {132},
number = {20},
pages = {204302},
abstract = {We report the effects of Si doping on the growth dynamics and size distribution of entirely catalyst-free GaAs nanowire (NW) arrays grown by selective area molecular beam epitaxy on SiO2-masked Si (111) substrates. Surprising improvements in the NW-array uniformity are found with increasing Si doping, while the growth of undoped NWs appears in a metastable regime, evidenced by large size and shape distributions, and the simultaneous presence of crystallites with tetrahedral termination. Correlating scanning electron microscopy and transmission electron microscopy investigations, we propose that the size and shape distributions are strongly linked to the underlying twin defect formation probabilities that govern the growth. Under the present growth conditions, Si-doping of GaAs NWs leads to a very high twin defect formation probability (∼0.4), while undoped NWs exhibit a nearly threefold decreased probability (∼0.15). By adopting a model for facet-mediated growth, we describe how the altered twin formation probabilities impact the competing growth of the relevant low-index NW facets, and hence, NW size and shape. Our model is further supported by a generic Monte Carlo simulation approach to highlight the role of twin defects in reproducing the experimentally observed size distributions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report the effects of Si doping on the growth dynamics and size distribution of entirely catalyst-free GaAs nanowire (NW) arrays grown by selective area molecular beam epitaxy on SiO2-masked Si (111) substrates. Surprising improvements in the NW-array uniformity are found with increasing Si doping, while the growth of undoped NWs appears in a metastable regime, evidenced by large size and shape distributions, and the simultaneous presence of crystallites with tetrahedral termination. Correlating scanning electron microscopy and transmission electron microscopy investigations, we propose that the size and shape distributions are strongly linked to the underlying twin defect formation probabilities that govern the growth. Under the present growth conditions, Si-doping of GaAs NWs leads to a very high twin defect formation probability (∼0.4), while undoped NWs exhibit a nearly threefold decreased probability (∼0.15). By adopting a model for facet-mediated growth, we describe how the altered twin formation probabilities impact the competing growth of the relevant low-index NW facets, and hence, NW size and shape. Our model is further supported by a generic Monte Carlo simulation approach to highlight the role of twin defects in reproducing the experimentally observed size distributions.
40.
T Weber, L Kühner, L Sortino, A B Mhenni, N P Wilson, J Kühne, J J Finley, S A Maier, A Tittl
Strong light-matter interaction with self-hybridized bound states in the continuum in monolithic van der Waals metasurfaces Journal Article
In: arXiv preprint arXiv:2209.01944, 2022.
@article{nokey,
title = {Strong light-matter interaction with self-hybridized bound states in the continuum in monolithic van der Waals metasurfaces},
author = {T Weber and L K\"{u}hner and L Sortino and A B Mhenni and N P Wilson and J K\"{u}hne and J J Finley and S A Maier and A Tittl},
url = {https://arxiv.org/abs/2209.01944},
doi = {https://doi.org/10.48550/arXiv.2209.01944},
year = {2022},
date = {2022-09-05},
journal = {arXiv preprint arXiv:2209.01944},
abstract = {Photonic bound states in the continuum (BICs) are a standout nanophotonic platform for strong light-matter coupling with transition metal dichalcogenides (TMDCs), but have so far mostly been employed as all-dielectric metasurfaces with adjacent TMDC layers, incurring limitations related to strain, mode overlap, and material integration. In this work, we experimentally demonstrate for the first time asymmetry-dependent BIC resonances in 2D arrays of monolithic metasurfaces composed solely of the nanostructured bulk TMDC WS2 with BIC modes exhibiting sharp and tailored linewidths, ideal for selectively enhancing light-matter interactions. Geometrical variation enables the tuning of the BIC resonances across the exciton resonance in bulk WS2, revealing the strong-coupling regime with an anti-crossing pattern and a Rabi splitting of 116 meV. The precise control over the radiative loss channel provided by the BIC concept is harnessed to tailor the Rabi splitting via a geometrical asymmetry parameter of the metasurface. Crucially, the coupling strength itself can be controlled and is shown to be independent of material-intrinsic losses. Our BIC-driven monolithic metasurface platform can readily incorporate other TMDCs or excitonic materials to deliver previously unavailable fundamental insights and practical device concepts for polaritonic applications.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Photonic bound states in the continuum (BICs) are a standout nanophotonic platform for strong light-matter coupling with transition metal dichalcogenides (TMDCs), but have so far mostly been employed as all-dielectric metasurfaces with adjacent TMDC layers, incurring limitations related to strain, mode overlap, and material integration. In this work, we experimentally demonstrate for the first time asymmetry-dependent BIC resonances in 2D arrays of monolithic metasurfaces composed solely of the nanostructured bulk TMDC WS2 with BIC modes exhibiting sharp and tailored linewidths, ideal for selectively enhancing light-matter interactions. Geometrical variation enables the tuning of the BIC resonances across the exciton resonance in bulk WS2, revealing the strong-coupling regime with an anti-crossing pattern and a Rabi splitting of 116 meV. The precise control over the radiative loss channel provided by the BIC concept is harnessed to tailor the Rabi splitting via a geometrical asymmetry parameter of the metasurface. Crucially, the coupling strength itself can be controlled and is shown to be independent of material-intrinsic losses. Our BIC-driven monolithic metasurface platform can readily incorporate other TMDCs or excitonic materials to deliver previously unavailable fundamental insights and practical device concepts for polaritonic applications.
39.
C Qian, V Villafañe, M Schalk, G V Astakhov, U Kentsch, M Helm, P Soubelet, N P Wilson, R Rizzato, S Mohr, A W Holleitner, D B Bucher, A V Stier, J J Finley
Unveiling the Zero-Phonon Line of the Boron Vacancy Center by Cavity-Enhanced Emission Journal Article
In: Nano Letters, vol. 22, no. 13, pp. 5137-5142, 2022, ISSN: 1530-6984.
@article{nokey,
title = {Unveiling the Zero-Phonon Line of the Boron Vacancy Center by Cavity-Enhanced Emission},
author = {C Qian and V Villafa\~{n}e and M Schalk and G V Astakhov and U Kentsch and M Helm and P Soubelet and N P Wilson and R Rizzato and S Mohr and A W Holleitner and D B Bucher and A V Stier and J J Finley},
url = {https://doi.org/10.1021/acs.nanolett.2c00739},
doi = {10.1021/acs.nanolett.2c00739},
issn = {1530-6984},
year = {2022},
date = {2022-06-27},
journal = {Nano Letters},
volume = {22},
number = {13},
pages = {5137-5142},
abstract = {Negatively charged boron vacancies (VB\textendash) in hexagonal boron nitride (hBN) exhibit a broad emission spectrum due to strong electron\textendashphonon coupling and Jahn\textendashTeller mixing of electronic states. As such, the direct measurement of the zero-phonon line (ZPL) of VB\textendash has remained elusive. Here, we measure the room-temperature ZPL wavelength to be 773 ± 2 nm by coupling the hBN layer to the high-Q nanobeam cavity. As the wavelength of cavity mode is tuned, we observe a pronounced intensity resonance, indicating the coupling to VB\textendash. Our observations are consistent with the spatial redistribution of VB\textendash emission. Spatially resolved measurements show a clear Purcell effect maximum at the midpoint of the nanobeam, in accord with the optical field distribution of the cavity mode. Our results are in good agreement with theoretical calculations, opening the way to using VB\textendash as cavity spin\textendashphoton interfaces.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Negatively charged boron vacancies (VB–) in hexagonal boron nitride (hBN) exhibit a broad emission spectrum due to strong electron–phonon coupling and Jahn–Teller mixing of electronic states. As such, the direct measurement of the zero-phonon line (ZPL) of VB– has remained elusive. Here, we measure the room-temperature ZPL wavelength to be 773 ± 2 nm by coupling the hBN layer to the high-Q nanobeam cavity. As the wavelength of cavity mode is tuned, we observe a pronounced intensity resonance, indicating the coupling to VB–. Our observations are consistent with the spatial redistribution of VB– emission. Spatially resolved measurements show a clear Purcell effect maximum at the midpoint of the nanobeam, in accord with the optical field distribution of the cavity mode. Our results are in good agreement with theoretical calculations, opening the way to using VB– as cavity spin–photon interfaces.
38.
C Qian, V Villafañe, P Soubelet, A Hötger, T Taniguchi, K Watanabe, N P Wilson, A V Stier, A W Holleitner, J J Finley
Nonlocal Exciton-Photon Interactions in Hybrid High-$Q$ Beam Nanocavities with Encapsulated $mathrmMoS_2$ Monolayers Journal Article
In: Physical Review Letters, vol. 128, no. 23, pp. 237403, 2022.
@article{nokey,
title = {Nonlocal Exciton-Photon Interactions in Hybrid High-$Q$ Beam Nanocavities with Encapsulated $mathrmMoS_2$ Monolayers},
author = {C Qian and V Villafa\~{n}e and P Soubelet and A H\"{o}tger and T Taniguchi and K Watanabe and N P Wilson and A V Stier and A W Holleitner and J J Finley},
url = {https://link.aps.org/doi/10.1103/PhysRevLett.128.237403},
doi = {10.1103/PhysRevLett.128.237403},
year = {2022},
date = {2022-06-10},
journal = {Physical Review Letters},
volume = {128},
number = {23},
pages = {237403},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
37.
N Bart, C Dangel, P Zajac, N Spitzer, J Ritzmann, M Schmidt, H G Babin, R Schott, S R Valentin, S Scholz, Y Wang, R Uppu, D Najer, M C Löbl, N Tomm, A Javadi, N O Antoniadis, L Midolo, K Müller, R J Warburton, P Lodahl, A D Wieck, J J Finley, A Ludwig
Wafer-scale epitaxial modulation of quantum dot density Journal Article
In: Nature Communications, vol. 13, no. 1, pp. 1633, 2022, ISSN: 2041-1723.
@article{nokey,
title = {Wafer-scale epitaxial modulation of quantum dot density},
author = {N Bart and C Dangel and P Zajac and N Spitzer and J Ritzmann and M Schmidt and H G Babin and R Schott and S R Valentin and S Scholz and Y Wang and R Uppu and D Najer and M C L\"{o}bl and N Tomm and A Javadi and N O Antoniadis and L Midolo and K M\"{u}ller and R J Warburton and P Lodahl and A D Wieck and J J Finley and A Ludwig},
url = {https://doi.org/10.1038/s41467-022-29116-8},
doi = {10.1038/s41467-022-29116-8},
issn = {2041-1723},
year = {2022},
date = {2022-03-28},
journal = {Nature Communications},
volume = {13},
number = {1},
pages = {1633},
abstract = {Precise control of the properties of semiconductor quantum dots (QDs) is vital for creating novel devices for quantum photonics and advanced opto-electronics. Suitable low QD-densities for single QD devices and experiments are challenging to control during epitaxy and are typically found only in limited regions of the wafer. Here, we demonstrate how conventional molecular beam epitaxy (MBE) can be used to modulate the density of optically active QDs in one- and two- dimensional patterns, while still retaining excellent quality. We find that material thickness gradients during layer-by-layer growth result in surface roughness modulations across the whole wafer. Growth on such templates strongly influences the QD nucleation probability. We obtain density modulations between 1 and 10 QDs/µm2 and periods ranging from several millimeters down to at least a few hundred microns. This method is universal and expected to be applicable to a wide variety of different semiconductor material systems. We apply the method to enable growth of ultra-low noise QDs across an entire 3-inch semiconductor wafer.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Precise control of the properties of semiconductor quantum dots (QDs) is vital for creating novel devices for quantum photonics and advanced opto-electronics. Suitable low QD-densities for single QD devices and experiments are challenging to control during epitaxy and are typically found only in limited regions of the wafer. Here, we demonstrate how conventional molecular beam epitaxy (MBE) can be used to modulate the density of optically active QDs in one- and two- dimensional patterns, while still retaining excellent quality. We find that material thickness gradients during layer-by-layer growth result in surface roughness modulations across the whole wafer. Growth on such templates strongly influences the QD nucleation probability. We obtain density modulations between 1 and 10 QDs/µm2 and periods ranging from several millimeters down to at least a few hundred microns. This method is universal and expected to be applicable to a wide variety of different semiconductor material systems. We apply the method to enable growth of ultra-low noise QDs across an entire 3-inch semiconductor wafer.
36.
J Klein, M Florian, A Hötger, A Steinhoff, A Delhomme, T Taniguchi, K Watanabe, F Jahnke, A W Holleitner, M Potemski, C Faugeras, A V Stier, J J Finley
Trions in $mathrmMoS_2$ are quantum superpositions of intra- and intervalley spin states Journal Article
In: Physical Review B, vol. 105, no. 4, pp. L041302, 2022.
@article{nokey,
title = {Trions in $mathrmMoS_2$ are quantum superpositions of intra- and intervalley spin states},
author = {J Klein and M Florian and A H\"{o}tger and A Steinhoff and A Delhomme and T Taniguchi and K Watanabe and F Jahnke and A W Holleitner and M Potemski and C Faugeras and A V Stier and J J Finley},
url = {https://link.aps.org/doi/10.1103/PhysRevB.105.L041302},
doi = {10.1103/PhysRevB.105.L041302},
year = {2022},
date = {2022-01-31},
journal = {Physical Review B},
volume = {105},
number = {4},
pages = {L041302},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
35.
T Grünleitner, A Henning, M Bissolo, A Kleibert, C F Vaz, A V Stier, J J Finley, I D Sharp
Electronically Tunable Transparent Conductive Thin Films for Scalable Integration of 2D Materials with Passive 2D–3D Interfaces Journal Article
In: Advanced Functional Materials, vol. n/a, no. n/a, pp. 2111343, 2022, ISSN: 1616-301X.
@article{nokey,
title = {Electronically Tunable Transparent Conductive Thin Films for Scalable Integration of 2D Materials with Passive 2D\textendash3D Interfaces},
author = {T Gr\"{u}nleitner and A Henning and M Bissolo and A Kleibert and C F Vaz and A V Stier and J J Finley and I D Sharp},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202111343},
doi = {https://doi.org/10.1002/adfm.202111343},
issn = {1616-301X},
year = {2022},
date = {2022-01-22},
journal = {Advanced Functional Materials},
volume = {n/a},
number = {n/a},
pages = {2111343},
abstract = {Abstract A novel transparent conductive support structure for scalable integration of 2D materials is demonstrated, providing an electronically passive 2D\textendash3D interface while also enabling facile interfacial charge transport. This structure, which comprises an evaporated nanocrystalline carbon (nc-C) film beneath nanometer-thin atomic layer deposited AlOx, is thermally stable and allows direct chemical vapor deposition of 2D materials onto the surface. The combination of spatial uniformity, enhanced charge screening, and low interface defect concentrations yields a tenfold enhancement of MoS2 photoluminescence intensity compared to flakes on conventional Si/SiO2, while also retaining the strong optical contrast for monolayer flakes. Tunneling across the ultrathin AlOx enables facile interfacial charge injection, which is utilized for high-resolution scanning electron microscopy and photoemission electron microscopy with no detectable charging. Thus, this combination of scalable fabrication and electronic conductivity across a weakly interacting 2D\textendash3D interface opens up new opportunities for device integration and characterization of 2D materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract A novel transparent conductive support structure for scalable integration of 2D materials is demonstrated, providing an electronically passive 2D–3D interface while also enabling facile interfacial charge transport. This structure, which comprises an evaporated nanocrystalline carbon (nc-C) film beneath nanometer-thin atomic layer deposited AlOx, is thermally stable and allows direct chemical vapor deposition of 2D materials onto the surface. The combination of spatial uniformity, enhanced charge screening, and low interface defect concentrations yields a tenfold enhancement of MoS2 photoluminescence intensity compared to flakes on conventional Si/SiO2, while also retaining the strong optical contrast for monolayer flakes. Tunneling across the ultrathin AlOx enables facile interfacial charge injection, which is utilized for high-resolution scanning electron microscopy and photoemission electron microscopy with no detectable charging. Thus, this combination of scalable fabrication and electronic conductivity across a weakly interacting 2D–3D interface opens up new opportunities for device integration and characterization of 2D materials.
34.
M M Petrić, M Kremser, M Barbone, A Nolinder, A Lyamkina, A V Stier, M Kaniber, K Müller, J J Finley
Tuning the Optical Properties of a MoSe2 Monolayer Using Nanoscale Plasmonic Antennas Journal Article
In: Nano Letters, vol. 22, no. 2, pp. 561-569, 2022, ISSN: 1530-6984.
@article{nokey,
title = {Tuning the Optical Properties of a MoSe2 Monolayer Using Nanoscale Plasmonic Antennas},
author = {M M Petri\'{c} and M Kremser and M Barbone and A Nolinder and A Lyamkina and A V Stier and M Kaniber and K M\"{u}ller and J J Finley},
url = {https://doi.org/10.1021/acs.nanolett.1c02676},
doi = {10.1021/acs.nanolett.1c02676},
issn = {1530-6984},
year = {2022},
date = {2022-01-03},
journal = {Nano Letters},
volume = {22},
number = {2},
pages = {561-569},
abstract = {Nanoplasmonic systems combined with optically active two-dimensional materials provide intriguing opportunities to explore and control light\textendashmatter interactions at extreme subwavelength length scales approaching the exciton Bohr radius. Here, we present room- and cryogenic-temperature investigations of a MoSe2 monolayer on individual gold dipole nanoantennas. By controlling nanoantenna size, the dipolar resonance is tuned relative to the exciton achieving a total tuning of ∼130 meV. Differential reflectance measurements performed on \>100 structures reveal an apparent avoided crossing between exciton and dipolar mode and an exciton\textendashplasmon coupling constant of g = 55 meV, representing g/(ℏωX) ≥ 3% of the transition energy. This places our hybrid system in the intermediate-coupling regime where spectra exhibit a characteristic Fano-like shape. We demonstrate active control by varying the polarization of the excitation light to programmably suppress coupling to the dipole mode. We further study the emerging optical signatures of the monolayer localized at dipole nanoantennas at 10 K.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Nanoplasmonic systems combined with optically active two-dimensional materials provide intriguing opportunities to explore and control light–matter interactions at extreme subwavelength length scales approaching the exciton Bohr radius. Here, we present room- and cryogenic-temperature investigations of a MoSe2 monolayer on individual gold dipole nanoantennas. By controlling nanoantenna size, the dipolar resonance is tuned relative to the exciton achieving a total tuning of ∼130 meV. Differential reflectance measurements performed on >100 structures reveal an apparent avoided crossing between exciton and dipolar mode and an exciton–plasmon coupling constant of g = 55 meV, representing g/(ℏωX) ≥ 3% of the transition energy. This places our hybrid system in the intermediate-coupling regime where spectra exhibit a characteristic Fano-like shape. We demonstrate active control by varying the polarization of the excitation light to programmably suppress coupling to the dipole mode. We further study the emerging optical signatures of the monolayer localized at dipole nanoantennas at 10 K.
33.
F Del Giudice, S Fust, P Schmiedeke, J Pantle, M Döblinger, A Ajay, S Meder, H Riedl, J J Finley, G Koblmüller
Epitaxial type-I and type-II InAs-AlAsSb core–shell nanowires on silicon Journal Article
In: Applied Physics Letters, vol. 119, no. 19, pp. 193102, 2021, ISSN: 0003-6951.
@article{nokey,
title = {Epitaxial type-I and type-II InAs-AlAsSb core\textendashshell nanowires on silicon},
author = {F Del Giudice and S Fust and P Schmiedeke and J Pantle and M D\"{o}blinger and A Ajay and S Meder and H Riedl and J J Finley and G Koblm\"{u}ller},
url = {https://doi.org/10.1063/5.0065867},
doi = {10.1063/5.0065867},
issn = {0003-6951},
year = {2021},
date = {2021-11-08},
journal = {Applied Physics Letters},
volume = {119},
number = {19},
pages = {193102},
abstract = {Low-bandgap semiconductor nanowires (NWs) attract considerable interest for mid-infrared (MIR) photonics and optoelectronics, where ideal candidate materials require surface-passivated core\textendashshell systems with large tunability in band offset, lineup, and emission wavelength while maintaining close lattice-matching conditions. Here, we propose and demonstrate epitaxial InAs\textendashAlAsSb core\textendashshell NW arrays on silicon (Si) that offer exceptional control over both the internal strain close to lattice-matching as well as band lineups tunable between type-I and type-II, with almost no analogue in the III\textendashV materials family. We develop direct monolithic growth of high-uniformity InAs\textendashAlAsSb NWs with wide tunability in shell composition and employ correlated Raman scattering and micro-photoluminescence spectroscopy to elaborate the interplay among hydrostatic strain, band lineup, and emission energy of the NW core luminescence tuned from ∼0.4 to 0.55 eV. Electronic structure calculations further support the experimentally observed tunability between type-I and type-II band lineups. The Si-integrated InAs-AlAsSb NW materials system holds large prospects not only for on-chip MIR photonics but also for other applications including high-speed transistors and NW-based hot carrier solar cells.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Low-bandgap semiconductor nanowires (NWs) attract considerable interest for mid-infrared (MIR) photonics and optoelectronics, where ideal candidate materials require surface-passivated core–shell systems with large tunability in band offset, lineup, and emission wavelength while maintaining close lattice-matching conditions. Here, we propose and demonstrate epitaxial InAs–AlAsSb core–shell NW arrays on silicon (Si) that offer exceptional control over both the internal strain close to lattice-matching as well as band lineups tunable between type-I and type-II, with almost no analogue in the III–V materials family. We develop direct monolithic growth of high-uniformity InAs–AlAsSb NWs with wide tunability in shell composition and employ correlated Raman scattering and micro-photoluminescence spectroscopy to elaborate the interplay among hydrostatic strain, band lineup, and emission energy of the NW core luminescence tuned from ∼0.4 to 0.55 eV. Electronic structure calculations further support the experimentally observed tunability between type-I and type-II band lineups. The Si-integrated InAs-AlAsSb NW materials system holds large prospects not only for on-chip MIR photonics but also for other applications including high-speed transistors and NW-based hot carrier solar cells.
32.
C Qian, V Villafañe, P Soubelet, A Hötger, T Taniguchi, K Watanabe, N P Wilson, A V Stier, A W Holleitner, J J Finley
Non-Local Exciton-Photon Interactions in Hybrid High-Q Nanocavities with Embedded hBN-Encapsulated MoS2 Monolayers Journal Article
In: arXiv preprint arXiv:2107.04387, 2021.
@article{nokey,
title = {Non-Local Exciton-Photon Interactions in Hybrid High-Q Nanocavities with Embedded hBN-Encapsulated MoS2 Monolayers},
author = {C Qian and V Villafa\~{n}e and P Soubelet and A H\"{o}tger and T Taniguchi and K Watanabe and N P Wilson and A V Stier and A W Holleitner and J J Finley},
url = {https://arxiv.org/abs/2107.04387},
doi = {arXiv:2107.04387v2},
year = {2021},
date = {2021-09-20},
journal = {arXiv preprint arXiv:2107.04387},
abstract = {Atomically thin semiconductors can be readily integrated into a wide range of nanophotonic architectures for applications in quantum photonics and novel optoelectronic devices. We report the observation of non-local interactions of textitfree trions in pristine hBN/MoS2/hBN heterostructures coupled to single mode (Q \>104) quasi 0D nanocavities. The high excitonic and photonic quality of the interaction system stem from our integrated nanofabrication approach simultaneously with the hBN encapsulation and the maximized local cavity field amplitude within the MoS2 monolayer. We observe a non-monotonic temperature dependence of the cavity-trion interaction strength, consistent with the non-local light-matter interactions in which the free trion diffuse over lengthscales comparable to the cavity mode volume. Our approach can be generalized to other optically active 2D materials, opening the way towards harnessing novel light-matter interaction regimes for applications in quantum photonics.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Atomically thin semiconductors can be readily integrated into a wide range of nanophotonic architectures for applications in quantum photonics and novel optoelectronic devices. We report the observation of non-local interactions of textitfree trions in pristine hBN/MoS2/hBN heterostructures coupled to single mode (Q >104) quasi 0D nanocavities. The high excitonic and photonic quality of the interaction system stem from our integrated nanofabrication approach simultaneously with the hBN encapsulation and the maximized local cavity field amplitude within the MoS2 monolayer. We observe a non-monotonic temperature dependence of the cavity-trion interaction strength, consistent with the non-local light-matter interactions in which the free trion diffuse over lengthscales comparable to the cavity mode volume. Our approach can be generalized to other optically active 2D materials, opening the way towards harnessing novel light-matter interaction regimes for applications in quantum photonics.
31.
A Thurn, J Bissinger, S Meinecke, P Schmiedeke, S S Oh, W W Chow, K Lüdge, G Koblmüller, J J Finley
Self-induced ultrafast electron-hole plasma temperature oscillations in nanowire lasers Journal Article
In: arXiv preprint arXiv:2108.11784, 2021.
@article{nokey,
title = {Self-induced ultrafast electron-hole plasma temperature oscillations in nanowire lasers},
author = {A Thurn and J Bissinger and S Meinecke and P Schmiedeke and S S Oh and W W Chow and K L\"{u}dge and G Koblm\"{u}ller and J J Finley},
url = {https://arxiv.org/abs/2108.11784},
doi = {arXiv:2108.11784v2},
year = {2021},
date = {2021-09-06},
journal = {arXiv preprint arXiv:2108.11784},
abstract = {Nanowire lasers can be monolithically and site-selectively integrated onto silicon photonic circuits. To assess their full potential for ultrafast opto-electronic devices, a detailed understanding of their lasing dynamics is crucial. However, the roles played by their resonator geometry and the microscopic processes that mediate energy exchange between the photonic, electronic, and phononic systems are largely unexplored. Here, we apply femtosecond pump-probe spectroscopy to show that GaAs-AlGaAs core-shell nanowire lasers exhibit sustained intensity oscillations with frequencies ranging from 160 GHz to 260 GHz. These dynamics are intricately linked to the strong interaction between the lasing mode and the gain material arising from their wavelength-scale dimensions. Combined with dynamic competition between photoinduced carrier heating and cooling via phonon scattering, this enables self-induced electron-hole plasma temperature oscillations, which modulate the laser output. We anticipate that our results will lead to new approaches for ultrafast intensity and phase modulation of chip-integrated nanoscale semiconductor lasers.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Nanowire lasers can be monolithically and site-selectively integrated onto silicon photonic circuits. To assess their full potential for ultrafast opto-electronic devices, a detailed understanding of their lasing dynamics is crucial. However, the roles played by their resonator geometry and the microscopic processes that mediate energy exchange between the photonic, electronic, and phononic systems are largely unexplored. Here, we apply femtosecond pump-probe spectroscopy to show that GaAs-AlGaAs core-shell nanowire lasers exhibit sustained intensity oscillations with frequencies ranging from 160 GHz to 260 GHz. These dynamics are intricately linked to the strong interaction between the lasing mode and the gain material arising from their wavelength-scale dimensions. Combined with dynamic competition between photoinduced carrier heating and cooling via phonon scattering, this enables self-induced electron-hole plasma temperature oscillations, which modulate the laser output. We anticipate that our results will lead to new approaches for ultrafast intensity and phase modulation of chip-integrated nanoscale semiconductor lasers.
30.
C Qian, V Villafane, P Soubelet, A Hötger, T Taniguchi, K Watanabe, N P Wilson, A V Stier, A W Holleitner, J J Finley
Strong coupling and non-local interactions in MoS2 monolayers coupled to high-Q nanocavities Journal Article
In: Measurement, vol. 495, no. 445, pp. 105, 2021.
@article{nokey,
title = {Strong coupling and non-local interactions in MoS2 monolayers coupled to high-Q nanocavities},
author = {C Qian and V Villafane and P Soubelet and A H\"{o}tger and T Taniguchi and K Watanabe and N P Wilson and A V Stier and A W Holleitner and J J Finley},
url = {https://ui.adsabs.harvard.edu/abs/2021arXiv210704387Q/abstract},
doi = {arXiv:2107.04387},
year = {2021},
date = {2021-07-02},
journal = {Measurement},
volume = {495},
number = {445},
pages = {105},
abstract = {Atomically thin semiconductors can be readily integrated into a wide range of nanophotonic architectures for applications in quantum photonics and novel optoelectronic devices. We report the observation of non-local interactions of textitfree trions in pristine hBN/MoS 2 /hBN heterostructures coupled to single mode (Q \>104 ) quasi 0D nanocavities. The high excitonic and photonic quality of the interaction system stem from our integrated nanofabrication approach simultaneously with the hBN encapsulation and the maximized local cavity field amplitude within the MoS 2 monolayer. We observe a non-monotonic temperature dependence of the cavity-trion interaction strength, consistent with the non-local light-matter interactions in which the free trion diffuse over lengthscales comparable to the cavity mode volume. Our approach can be generalized to other optically active 2D materials, opening the way towards harnessing novel light-matter interaction regimes for applications in quantum photonics.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Atomically thin semiconductors can be readily integrated into a wide range of nanophotonic architectures for applications in quantum photonics and novel optoelectronic devices. We report the observation of non-local interactions of textitfree trions in pristine hBN/MoS 2 /hBN heterostructures coupled to single mode (Q >104 ) quasi 0D nanocavities. The high excitonic and photonic quality of the interaction system stem from our integrated nanofabrication approach simultaneously with the hBN encapsulation and the maximized local cavity field amplitude within the MoS 2 monolayer. We observe a non-monotonic temperature dependence of the cavity-trion interaction strength, consistent with the non-local light-matter interactions in which the free trion diffuse over lengthscales comparable to the cavity mode volume. Our approach can be generalized to other optically active 2D materials, opening the way towards harnessing novel light-matter interaction regimes for applications in quantum photonics.
29.
J Klein, J Wierzbowski, P Soubelet, T Brumme, L Maschio, A Kuc, K Müller, A V Stier, J J Finley
Electrical control of orbital and vibrational interlayer coupling in bi-and trilayer 2H-MoS $ _2$ Journal Article
In: arXiv preprint arXiv:2106.11839, 2021.
@article{nokey,
title = {Electrical control of orbital and vibrational interlayer coupling in bi-and trilayer 2H-MoS $ _2$},
author = {J Klein and J Wierzbowski and P Soubelet and T Brumme and L Maschio and A Kuc and K M\"{u}ller and A V Stier and J J Finley},
url = {https://arxiv.org/abs/2106.11839},
doi = {arXiv:2106.11839v1},
year = {2021},
date = {2021-06-22},
journal = {arXiv preprint arXiv:2106.11839},
abstract = {Manipulating electronic interlayer coupling in layered van der Waals (vdW) materials is essential for designing opto-electronic devices. Here, we control vibrational and electronic interlayer coupling in bi- and trilayer 2H-MoS2 using large external electric fields in a micro-capacitor device. The electric field lifts Raman selection rules and activates phonon modes in excellent agreement with ab-initio calculations. Through polarization resolved photoluminescence spectroscopy in the same device, we observe a strongly tunable valley dichroism with maximum circular polarization degree of ∼60% in bilayer and ∼35% in trilayer MoS2 that are fully consistent with a rate equation model which includes input from electronic band structure calculations. We identify the highly delocalized electron wave function between the layers close to the high symmetry Q points as the origin of the tunable circular dichroism. Our results demonstrate the possibility of electric field tunable interlayer coupling for controlling emergent spin-valley physics and hybridization driven effects in vdW materials and their heterostructures.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Manipulating electronic interlayer coupling in layered van der Waals (vdW) materials is essential for designing opto-electronic devices. Here, we control vibrational and electronic interlayer coupling in bi- and trilayer 2H-MoS2 using large external electric fields in a micro-capacitor device. The electric field lifts Raman selection rules and activates phonon modes in excellent agreement with ab-initio calculations. Through polarization resolved photoluminescence spectroscopy in the same device, we observe a strongly tunable valley dichroism with maximum circular polarization degree of ∼60% in bilayer and ∼35% in trilayer MoS2 that are fully consistent with a rate equation model which includes input from electronic band structure calculations. We identify the highly delocalized electron wave function between the layers close to the high symmetry Q points as the origin of the tunable circular dichroism. Our results demonstrate the possibility of electric field tunable interlayer coupling for controlling emergent spin-valley physics and hybridization driven effects in vdW materials and their heterostructures.
28.
E Mitterreiter, B Schuler, A Micevic, D Hernangómez-Pérez, K Barthelmi, K A Cochrane, J Kiemle, F Sigger, J Klein, E Wong, E S Barnard, K Watanabe, T Taniguchi, M Lorke, F Jahnke, J J Finley, A M Schwartzberg, D Y Qiu, S Refaely-Abramson, A W Holleitner, A Weber-Bargioni, C Kastl
The role of chalcogen vacancies for atomic defect emission in MoS2 Journal Article
In: Nature Communications, vol. 12, no. 1, pp. 3822, 2021, ISSN: 2041-1723.
@article{nokey,
title = {The role of chalcogen vacancies for atomic defect emission in MoS2},
author = {E Mitterreiter and B Schuler and A Micevic and D Hernang\'{o}mez-P\'{e}rez and K Barthelmi and K A Cochrane and J Kiemle and F Sigger and J Klein and E Wong and E S Barnard and K Watanabe and T Taniguchi and M Lorke and F Jahnke and J J Finley and A M Schwartzberg and D Y Qiu and S Refaely-Abramson and A W Holleitner and A Weber-Bargioni and C Kastl},
url = {https://doi.org/10.1038/s41467-021-24102-y},
doi = {10.1038/s41467-021-24102-y},
issn = {2041-1723},
year = {2021},
date = {2021-06-22},
journal = {Nature Communications},
volume = {12},
number = {1},
pages = {3822},
abstract = {For two-dimensional (2D) layered semiconductors, control over atomic defects and understanding of their electronic and optical functionality represent major challenges towards developing a mature semiconductor technology using such materials. Here, we correlate generation, optical spectroscopy, atomic resolution imaging, and ab initio theory of chalcogen vacancies in monolayer MoS2. Chalcogen vacancies are selectively generated by in-vacuo annealing, but also focused ion beam exposure. The defect generation rate, atomic imaging and the optical signatures support this claim. We discriminate the narrow linewidth photoluminescence signatures of vacancies, resulting predominantly from localized defect orbitals, from broad luminescence features in the same spectral range, resulting from adsorbates. Vacancies can be patterned with a precision below 10 nm by ion beams, show single photon emission, and open the possibility for advanced defect engineering of 2D semiconductors at the ultimate scale.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
For two-dimensional (2D) layered semiconductors, control over atomic defects and understanding of their electronic and optical functionality represent major challenges towards developing a mature semiconductor technology using such materials. Here, we correlate generation, optical spectroscopy, atomic resolution imaging, and ab initio theory of chalcogen vacancies in monolayer MoS2. Chalcogen vacancies are selectively generated by in-vacuo annealing, but also focused ion beam exposure. The defect generation rate, atomic imaging and the optical signatures support this claim. We discriminate the narrow linewidth photoluminescence signatures of vacancies, resulting predominantly from localized defect orbitals, from broad luminescence features in the same spectral range, resulting from adsorbates. Vacancies can be patterned with a precision below 10 nm by ion beams, show single photon emission, and open the possibility for advanced defect engineering of 2D semiconductors at the ultimate scale.
27.
T Neumann, S Feldmann, P Moser, A Delhomme, J Zerhoch, T Van De Goor, S Wang, M Dyksik, T Winkler, J J Finley, P Plochocka, M S Brandt, C Faugeras, A V Stier, F Deschler
In: Nature Communications, vol. 12, no. 1, pp. 3489, 2021, ISSN: 2041-1723.
@article{nokey,
title = {Manganese doping for enhanced magnetic brightening and circular polarization control of dark excitons in paramagnetic layered hybrid metal-halide perovskites},
author = {T Neumann and S Feldmann and P Moser and A Delhomme and J Zerhoch and T Van De Goor and S Wang and M Dyksik and T Winkler and J J Finley and P Plochocka and M S Brandt and C Faugeras and A V Stier and F Deschler},
url = {https://doi.org/10.1038/s41467-021-23602-1},
doi = {10.1038/s41467-021-23602-1},
issn = {2041-1723},
year = {2021},
date = {2021-06-09},
journal = {Nature Communications},
volume = {12},
number = {1},
pages = {3489},
abstract = {Materials combining semiconductor functionalities with spin control are desired for the advancement of quantum technologies. Here, we study the magneto-optical properties of novel paramagnetic Ruddlesden-Popper hybrid perovskites Mn:(PEA)2PbI4 (PEA = phenethylammonium) and report magnetically brightened excitonic luminescence with strong circular polarization from the interaction with isolated Mn2+ ions. Using a combination of superconducting quantum interference device (SQUID) magnetometry, magneto-absorption and transient optical spectroscopy, we find that a dark exciton population is brightened by state mixing with the bright excitons in the presence of a magnetic field. Unexpectedly, the circular polarization of the dark exciton luminescence follows the Brillouin-shaped magnetization with a saturation polarization of 13% at 4 K and 6 T. From high-field transient magneto-luminescence we attribute our observations to spin-dependent exciton dynamics at early times after excitation, with first indications for a Mn-mediated spin-flip process. Our findings demonstrate manganese doping as a powerful approach to control excitonic spin physics in Ruddlesden-Popper perovskites, which will stimulate research on this highly tuneable material platform with promise for tailored interactions between magnetic moments and excitonic states.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Materials combining semiconductor functionalities with spin control are desired for the advancement of quantum technologies. Here, we study the magneto-optical properties of novel paramagnetic Ruddlesden-Popper hybrid perovskites Mn:(PEA)2PbI4 (PEA = phenethylammonium) and report magnetically brightened excitonic luminescence with strong circular polarization from the interaction with isolated Mn2+ ions. Using a combination of superconducting quantum interference device (SQUID) magnetometry, magneto-absorption and transient optical spectroscopy, we find that a dark exciton population is brightened by state mixing with the bright excitons in the presence of a magnetic field. Unexpectedly, the circular polarization of the dark exciton luminescence follows the Brillouin-shaped magnetization with a saturation polarization of 13% at 4 K and 6 T. From high-field transient magneto-luminescence we attribute our observations to spin-dependent exciton dynamics at early times after excitation, with first indications for a Mn-mediated spin-flip process. Our findings demonstrate manganese doping as a powerful approach to control excitonic spin physics in Ruddlesden-Popper perovskites, which will stimulate research on this highly tuneable material platform with promise for tailored interactions between magnetic moments and excitonic states.
26.
P Schmiedeke, A Thurn, S Matich, M Döblinger, J J Finley, G Koblmüller
Low-threshold strain-compensated InGaAs/(In,Al)GaAs multi-quantum well nanowire lasers emitting near 1.3 μm at room temperature Journal Article
In: Applied Physics Letters, vol. 118, no. 22, 2021, ISSN: 0003-6951.
@article{nokey,
title = {Low-threshold strain-compensated InGaAs/(In,Al)GaAs multi-quantum well nanowire lasers emitting near 1.3 μm at room temperature},
author = {P Schmiedeke and A Thurn and S Matich and M D\"{o}blinger and J J Finley and G Koblm\"{u}ller},
url = {https://doi.org/10.1063/5.0048807},
doi = {10.1063/5.0048807},
issn = {0003-6951},
year = {2021},
date = {2021-05-31},
journal = {Applied Physics Letters},
volume = {118},
number = {22},
abstract = {Realizing telecom-band lasing in GaAs-based nanowires (NW) with low bandgap gain media has proven to be notoriously difficult due to the high compressive strain built up in the active regions. Here, we demonstrate an advanced coaxial GaAs-InGaAs multi-quantum well (MQW) nanowire laser that solves previous limitations by the introduction of a strain compensating InAlGaAs buffer layer between the GaAs core and the MQW active region. Using a buffer layer thickness comparable to the core diameter applies a significant tensile strain to the GaAs core which efficiently minimizes the compressive strain in the InGaAs MQW and enables large In-content without plastic relaxation. Experimental verification is shown for NW-lasers with an In-content of up to 40% in the MQW, evidencing a clear strain-relieved redshift of the lasing emission and a strong reduction of the lasing threshold compared to highly strained MQWs in state-of-the-art GaAs NW-lasers. This way we achieve optically pumped room temperature lasing operation with a threshold below 50 μJ cm−2 in the telecom O-band close to 1.3 μm.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Realizing telecom-band lasing in GaAs-based nanowires (NW) with low bandgap gain media has proven to be notoriously difficult due to the high compressive strain built up in the active regions. Here, we demonstrate an advanced coaxial GaAs-InGaAs multi-quantum well (MQW) nanowire laser that solves previous limitations by the introduction of a strain compensating InAlGaAs buffer layer between the GaAs core and the MQW active region. Using a buffer layer thickness comparable to the core diameter applies a significant tensile strain to the GaAs core which efficiently minimizes the compressive strain in the InGaAs MQW and enables large In-content without plastic relaxation. Experimental verification is shown for NW-lasers with an In-content of up to 40% in the MQW, evidencing a clear strain-relieved redshift of the lasing emission and a strong reduction of the lasing threshold compared to highly strained MQWs in state-of-the-art GaAs NW-lasers. This way we achieve optically pumped room temperature lasing operation with a threshold below 50 μJ cm−2 in the telecom O-band close to 1.3 μm.
25.
J Klein, A Hötger, M Florian, A Steinhoff, A Delhomme, T Taniguchi, K Watanabe, F Jahnke, A W Holleitner, M Potemski, C Faugeras, J J Finley, A V Stier
Controlling exciton many-body states by the electric-field effect in monolayer $mathrmMoS_2$ Journal Article
In: Physical Review Research, vol. 3, no. 2, pp. L022009, 2021.
@article{nokey,
title = {Controlling exciton many-body states by the electric-field effect in monolayer $mathrmMoS_2$},
author = {J Klein and A H\"{o}tger and M Florian and A Steinhoff and A Delhomme and T Taniguchi and K Watanabe and F Jahnke and A W Holleitner and M Potemski and C Faugeras and J J Finley and A V Stier},
url = {https://link.aps.org/doi/10.1103/PhysRevResearch.3.L022009},
doi = {10.1103/PhysRevResearch.3.L022009},
year = {2021},
date = {2021-04-30},
journal = {Physical Review Research},
volume = {3},
number = {2},
pages = {L022009},
abstract = {We report magneto-optical spectroscopy of gated monolayer
MoS2 in high magnetic fields up to 28T and obtain new insights on the many-body interaction of neutral and charged excitons with the resident charges of distinct spin and valley texture. For neutral excitons at low electron doping, we observe a nonlinear valley Zeeman shift due to dipolar spin-interactions that depends sensitively on the local carrier concentration. As the Fermi energy increases to dominate over the other relevant energy scales in the system, the magneto-optical response depends on the occupation of the fully spin-polarized Landau levels (LL) in both K/K′ valleys. This manifests itself in a many-body state. Our experiments demonstrate that the exciton in monolayer semiconductors is only a single particle boson close to charge neutrality. We find that away from charge neutrality it smoothly transitions into polaronic states with a distinct spin-valley flavor that is defined by the LL quantized spin and valley texture.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report magneto-optical spectroscopy of gated monolayer
MoS2 in high magnetic fields up to 28T and obtain new insights on the many-body interaction of neutral and charged excitons with the resident charges of distinct spin and valley texture. For neutral excitons at low electron doping, we observe a nonlinear valley Zeeman shift due to dipolar spin-interactions that depends sensitively on the local carrier concentration. As the Fermi energy increases to dominate over the other relevant energy scales in the system, the magneto-optical response depends on the occupation of the fully spin-polarized Landau levels (LL) in both K/K′ valleys. This manifests itself in a many-body state. Our experiments demonstrate that the exciton in monolayer semiconductors is only a single particle boson close to charge neutrality. We find that away from charge neutrality it smoothly transitions into polaronic states with a distinct spin-valley flavor that is defined by the LL quantized spin and valley texture.
MoS2 in high magnetic fields up to 28T and obtain new insights on the many-body interaction of neutral and charged excitons with the resident charges of distinct spin and valley texture. For neutral excitons at low electron doping, we observe a nonlinear valley Zeeman shift due to dipolar spin-interactions that depends sensitively on the local carrier concentration. As the Fermi energy increases to dominate over the other relevant energy scales in the system, the magneto-optical response depends on the occupation of the fully spin-polarized Landau levels (LL) in both K/K′ valleys. This manifests itself in a many-body state. Our experiments demonstrate that the exciton in monolayer semiconductors is only a single particle boson close to charge neutrality. We find that away from charge neutrality it smoothly transitions into polaronic states with a distinct spin-valley flavor that is defined by the LL quantized spin and valley texture.
24.
A Hötger, J Klein, K Barthelmi, L Sigl, F Sigger, W Männer, S Gyger, M Florian, M Lorke, F Jahnke, T Taniguchi, K Watanabe, K D Jöns, U Wurstbauer, C Kastl, K Müller, J J Finley, A W Holleitner
Gate-Switchable Arrays of Quantum Light Emitters in Contacted Monolayer MoS2 van der Waals Heterodevices Journal Article
In: Nano Letters, vol. 21, no. 2, pp. 1040-1046, 2021, ISSN: 1530-6984.
@article{,
title = {Gate-Switchable Arrays of Quantum Light Emitters in Contacted Monolayer MoS2 van der Waals Heterodevices},
author = {A H\"{o}tger and J Klein and K Barthelmi and L Sigl and F Sigger and W M\"{a}nner and S Gyger and M Florian and M Lorke and F Jahnke and T Taniguchi and K Watanabe and K D J\"{o}ns and U Wurstbauer and C Kastl and K M\"{u}ller and J J Finley and A W Holleitner},
url = {https://doi.org/10.1021/acs.nanolett.0c04222},
doi = {10.1021/acs.nanolett.0c04222},
issn = {1530-6984},
year = {2021},
date = {2021-01-27},
journal = {Nano Letters},
volume = {21},
number = {2},
pages = {1040-1046},
abstract = {We demonstrate electrostatic switching of individual, site-selectively generated matrices of single photon emitters (SPEs) in MoS2 van der Waals heterodevices. We contact monolayers of MoS2 in field-effect devices with graphene gates and hexagonal boron nitride as the dielectric and graphite as bottom gates. After the assembly of such gate-tunable heterodevices, we demonstrate how arrays of defects, that serve as quantum emitters, can be site-selectively generated in the monolayer MoS2 by focused helium ion irradiation. The SPEs are sensitive to the charge carrier concentration in the MoS2 and switch on and off similar to the neutral exciton in MoS2 for moderate electron doping. The demonstrated scheme is a first step for producing scalable, gate-addressable, and gate-switchable arrays of quantum light emitters in MoS2 heterostacks.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We demonstrate electrostatic switching of individual, site-selectively generated matrices of single photon emitters (SPEs) in MoS2 van der Waals heterodevices. We contact monolayers of MoS2 in field-effect devices with graphene gates and hexagonal boron nitride as the dielectric and graphite as bottom gates. After the assembly of such gate-tunable heterodevices, we demonstrate how arrays of defects, that serve as quantum emitters, can be site-selectively generated in the monolayer MoS2 by focused helium ion irradiation. The SPEs are sensitive to the charge carrier concentration in the MoS2 and switch on and off similar to the neutral exciton in MoS2 for moderate electron doping. The demonstrated scheme is a first step for producing scalable, gate-addressable, and gate-switchable arrays of quantum light emitters in MoS2 heterostacks.
23.
J Klein, L Sigl, S Gyger, K Barthelmi, M Florian, S Rey, T Taniguchi, K Watanabe, F Jahnke, C Kastl, V Zwiller, K D Jöns, K Müller, U Wurstbauer, J J Finley, A W Holleitner
Engineering the Luminescence and Generation of Individual Defect Emitters in Atomically Thin MoS2 Journal Article
In: ACS Photonics, 2021.
@article{,
title = {Engineering the Luminescence and Generation of Individual Defect Emitters in Atomically Thin MoS2},
author = {J Klein and L Sigl and S Gyger and K Barthelmi and M Florian and S Rey and T Taniguchi and K Watanabe and F Jahnke and C Kastl and V Zwiller and K D J\"{o}ns and K M\"{u}ller and U Wurstbauer and J J Finley and A W Holleitner},
url = {https://doi.org/10.1021/acsphotonics.0c01907},
doi = {10.1021/acsphotonics.0c01907},
year = {2021},
date = {2021-01-21},
journal = {ACS Photonics},
abstract = {We demonstrate the on-demand creation and positioning of photon emitters in atomically thin MoS2 with very narrow ensemble broadening and negligible background luminescence. Focused helium-ion beam irradiation creates 100s to 1000s of such mono-typical emitters at specific positions in the MoS2 monolayers. Individually measured photon emitters show antibunching behavior with a g2(0) ∼ 0.23 and 0.27. From a statistical analysis, we extract the creation yield of the He-ion induced photon emitters in MoS2 as a function of the exposed area, as well as the total yield of single emitters as a function of the number of He ions when single spots are irradiated by He ions. We reach probabilities as high as 18% for the generation of individual and spectrally clean photon emitters per irradiated single site. Our results firmly establish 2D materials as a platform for photon emitters with unprecedented control of position as well as photophysical properties owing to the all-interfacial nature.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We demonstrate the on-demand creation and positioning of photon emitters in atomically thin MoS2 with very narrow ensemble broadening and negligible background luminescence. Focused helium-ion beam irradiation creates 100s to 1000s of such mono-typical emitters at specific positions in the MoS2 monolayers. Individually measured photon emitters show antibunching behavior with a g2(0) ∼ 0.23 and 0.27. From a statistical analysis, we extract the creation yield of the He-ion induced photon emitters in MoS2 as a function of the exposed area, as well as the total yield of single emitters as a function of the number of He ions when single spots are irradiated by He ions. We reach probabilities as high as 18% for the generation of individual and spectrally clean photon emitters per irradiated single site. Our results firmly establish 2D materials as a platform for photon emitters with unprecedented control of position as well as photophysical properties owing to the all-interfacial nature.
22.
X Dong, H Li, Z Jiang, T Grünleitner, İ Güler, J Dong, K Wang, M H Köhler, M Jakobi, B H Menze, A K Yetisen, I D Sharp, A V Stier, J J Finley, A W Koch
3D Deep Learning Enables Accurate Layer Mapping of 2D Materials Journal Article
In: ACS Nano, vol. 15, no. 2, pp. 3139-3151, 2021, ISSN: 1936-0851.
@article{,
title = {3D Deep Learning Enables Accurate Layer Mapping of 2D Materials},
author = {X Dong and H Li and Z Jiang and T Gr\"{u}nleitner and \.{I} G\"{u}ler and J Dong and K Wang and M H K\"{o}hler and M Jakobi and B H Menze and A K Yetisen and I D Sharp and A V Stier and J J Finley and A W Koch},
url = {https://doi.org/10.1021/acsnano.0c09685},
doi = {10.1021/acsnano.0c09685},
issn = {1936-0851},
year = {2021},
date = {2021-01-19},
journal = {ACS Nano},
volume = {15},
number = {2},
pages = {3139-3151},
abstract = {Layered, two-dimensional (2D) materials are promising for next-generation photonics devices. Typically, the thickness of mechanically cleaved flakes and chemical vapor deposited thin films is distributed randomly over a large area, where accurate identification of atomic layer numbers is time-consuming. Hyperspectral imaging microscopy yields spectral information that can be used to distinguish the spectral differences of varying thickness specimens. However, its spatial resolution is relatively low due to the spectral imaging nature. In this work, we present a 3D deep learning solution called DALM (deep-learning-enabled atomic layer mapping) to merge hyperspectral reflection images (high spectral resolution) and RGB images (high spatial resolution) for the identification and segmentation of MoS2 flakes with mono-, bi-, tri-, and multilayer thicknesses. DALM is trained on a small set of labeled images, automatically predicts layer distributions and segments individual layers with high accuracy, and shows robustness to illumination and contrast variations. Further, we show its advantageous performance over the state-of-the-art model that is solely based on RGB microscope images. This AI-supported technique with high speed, spatial resolution, and accuracy allows for reliable computer-aided identification of atomically thin materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Layered, two-dimensional (2D) materials are promising for next-generation photonics devices. Typically, the thickness of mechanically cleaved flakes and chemical vapor deposited thin films is distributed randomly over a large area, where accurate identification of atomic layer numbers is time-consuming. Hyperspectral imaging microscopy yields spectral information that can be used to distinguish the spectral differences of varying thickness specimens. However, its spatial resolution is relatively low due to the spectral imaging nature. In this work, we present a 3D deep learning solution called DALM (deep-learning-enabled atomic layer mapping) to merge hyperspectral reflection images (high spectral resolution) and RGB images (high spatial resolution) for the identification and segmentation of MoS2 flakes with mono-, bi-, tri-, and multilayer thicknesses. DALM is trained on a small set of labeled images, automatically predicts layer distributions and segments individual layers with high accuracy, and shows robustness to illumination and contrast variations. Further, we show its advantageous performance over the state-of-the-art model that is solely based on RGB microscope images. This AI-supported technique with high speed, spatial resolution, and accuracy allows for reliable computer-aided identification of atomically thin materials.
21.
M M Petrić, M Kremser, M Barbone, Y Qin, Y Sayyad, Y Shen, S Tongay, J J Finley, A R Botello-Méndez, K Müller
Raman spectrum of Janus transition metal dichalcogenide monolayers WSSe and MoSSe Journal Article
In: Physical Review B, vol. 103, no. 3, pp. 035414, 2021.
@article{,
title = {Raman spectrum of Janus transition metal dichalcogenide monolayers WSSe and MoSSe},
author = {M M Petri\'{c} and M Kremser and M Barbone and Y Qin and Y Sayyad and Y Shen and S Tongay and J J Finley and A R Botello-M\'{e}ndez and K M\"{u}ller},
url = {https://link.aps.org/doi/10.1103/PhysRevB.103.035414},
doi = {10.1103/PhysRevB.103.035414},
year = {2021},
date = {2021-01-15},
journal = {Physical Review B},
volume = {103},
number = {3},
pages = {035414},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
20.
P Soubelet, J Klein, J Wierzbowski, R Silvioli, F Sigger, A V Stier, K Gallo, J J Finley
Charged Exciton Kinetics in Monolayer MoSe2 near Ferroelectric Domain Walls in Periodically Poled LiNbO3 Journal Article
In: Nano Letters, vol. 21, no. 2, pp. 959-966, 2021, ISSN: 1530-6984.
@article{,
title = {Charged Exciton Kinetics in Monolayer MoSe2 near Ferroelectric Domain Walls in Periodically Poled LiNbO3},
author = {P Soubelet and J Klein and J Wierzbowski and R Silvioli and F Sigger and A V Stier and K Gallo and J J Finley},
url = {https://doi.org/10.1021/acs.nanolett.0c03810},
doi = {10.1021/acs.nanolett.0c03810},
issn = {1530-6984},
year = {2021},
date = {2021-01-11},
journal = {Nano Letters},
volume = {21},
number = {2},
pages = {959-966},
abstract = {Monolayer semiconducting transition metal dichalcogenides are a strongly emergent platform for exploring quantum phenomena in condensed matter, building novel optoelectronic devices with enhanced functionalities. Because of their atomic thickness, their excitonic optical response is highly sensitive to their dielectric environment. In this work, we explore the optical properties of monolayer thick MoSe2 straddling domain wall boundaries in periodically poled LiNbO3. Spatially resolved photoluminescence experiments reveal spatial sorting of charge and photogenerated neutral and charged excitons across the boundary. Our results reveal evidence for extremely large in-plane electric fields of ≃4000 kV/cm at the domain wall whose effect is manifested in exciton dissociation and routing of free charges and trions toward oppositely poled domains and a nonintuitive spatial intensity dependence. By modeling our result using drift-diffusion and continuity equations, we obtain excellent qualitative agreement with our observations and have explained the observed spatial luminescence modulation using realistic material parameters.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Monolayer semiconducting transition metal dichalcogenides are a strongly emergent platform for exploring quantum phenomena in condensed matter, building novel optoelectronic devices with enhanced functionalities. Because of their atomic thickness, their excitonic optical response is highly sensitive to their dielectric environment. In this work, we explore the optical properties of monolayer thick MoSe2 straddling domain wall boundaries in periodically poled LiNbO3. Spatially resolved photoluminescence experiments reveal spatial sorting of charge and photogenerated neutral and charged excitons across the boundary. Our results reveal evidence for extremely large in-plane electric fields of ≃4000 kV/cm at the domain wall whose effect is manifested in exciton dissociation and routing of free charges and trions toward oppositely poled domains and a nonintuitive spatial intensity dependence. By modeling our result using drift-diffusion and continuity equations, we obtain excellent qualitative agreement with our observations and have explained the observed spatial luminescence modulation using realistic material parameters.
19.
D Ruhstorfer, A Lang, S Matich, M Döblinger, H Riedl, J J Finley, G Koblmüller
Growth dynamics and compositional structure in periodic InAsSb nanowire arrays on Si (111) grown by selective area molecular beam epitaxy Journal Article
In: Nanotechnology, vol. 32, no. 13, pp. 135604, 2021, ISSN: 0957-4484.
@article{,
title = {Growth dynamics and compositional structure in periodic InAsSb nanowire arrays on Si (111) grown by selective area molecular beam epitaxy},
author = {D Ruhstorfer and A Lang and S Matich and M D\"{o}blinger and H Riedl and J J Finley and G Koblm\"{u}ller},
issn = {0957-4484},
year = {2021},
date = {2021-01-08},
journal = {Nanotechnology},
volume = {32},
number = {13},
pages = {135604},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
18.
L Wolz, C Heshmatpour, A Perri, D Polli, G Cerullo, J J Finley, E Thyrhaug, J Hauer, A V Stier
Time-domain photocurrent spectroscopy based on a common-path birefringent interferometer Journal Article
In: Review of Scientific Instruments, vol. 91, no. 12, pp. 123101, 2020.
@article{,
title = {Time-domain photocurrent spectroscopy based on a common-path birefringent interferometer},
author = {L Wolz and C Heshmatpour and A Perri and D Polli and G Cerullo and J J Finley and E Thyrhaug and J Hauer and A V Stier},
url = {https://aip.scitation.org/doi/abs/10.1063/5.0023543},
doi = {10.1063/5.0023543},
year = {2020},
date = {2020-12-02},
urldate = {2020-12-02},
journal = {Review of Scientific Instruments},
volume = {91},
number = {12},
pages = {123101},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
17.
N Bart, C Dangel, P Zajac, N Spitzer, J Ritzmann, M Schmidt, K Müller, A Wieck, J J Finley, A Ludwig
Wafer-Scale Epitaxial Positioning of Quantum Dots Journal Article
In: arXiv e-prints, pp. arXiv: 2011.10632, 2020.
@article{nokey,
title = {Wafer-Scale Epitaxial Positioning of Quantum Dots},
author = {N Bart and C Dangel and P Zajac and N Spitzer and J Ritzmann and M Schmidt and K M\"{u}ller and A Wieck and J J Finley and A Ludwig},
url = {https://arxiv.org/abs/2011.10632v2},
doi = {arXiv:2011.10632v2},
year = {2020},
date = {2020-11-20},
urldate = {2020-11-20},
journal = {arXiv e-prints},
pages = {arXiv: 2011.10632},
abstract = {Precise control of the properties of semiconductor quantum dots (QDs) is vital for creating novel devices for quantum photonics and advanced opto-electronics. Suitable low QD-density for single QD devices and experiments are challenging to control during epitaxy and are typically found only in limited regions of the wafer. Here, we demonstrate how conventional molecular beam epitaxy (MBE) can be used to modulate the density of optically active QDs in one- and two- dimensional patterns, while still retaining excellent quality. We find that material thickness gradients during layer-by-layer growth result in surface roughness modulations across the whole wafer. Growth on such templates strongly influences the QD nucleation probability. We obtain density modulations between 1 and 10 QDs/μm2 and periods ranging from several millimeters down to at least a few hundred microns. This novel method is universal and expected to be applicable to a wide variety of different semiconductor material systems. We apply the method to enable growth of ultra-low noise QDs across an entire 3-inch semiconductor wafer.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Precise control of the properties of semiconductor quantum dots (QDs) is vital for creating novel devices for quantum photonics and advanced opto-electronics. Suitable low QD-density for single QD devices and experiments are challenging to control during epitaxy and are typically found only in limited regions of the wafer. Here, we demonstrate how conventional molecular beam epitaxy (MBE) can be used to modulate the density of optically active QDs in one- and two- dimensional patterns, while still retaining excellent quality. We find that material thickness gradients during layer-by-layer growth result in surface roughness modulations across the whole wafer. Growth on such templates strongly influences the QD nucleation probability. We obtain density modulations between 1 and 10 QDs/μm2 and periods ranging from several millimeters down to at least a few hundred microns. This novel method is universal and expected to be applicable to a wide variety of different semiconductor material systems. We apply the method to enable growth of ultra-low noise QDs across an entire 3-inch semiconductor wafer.
16.
D B Trivedi, G Turgut, Y Qin, M Y Sayyad, D Hajra, M Howell, L Liu, S Yang, N H Patoary, H Li, M M Petrić, M Meyer, M Kremser, M Barbone, G Soavi, A V Stier, K Müller, S Yang, I S Esqueda, H Zhuang, J J Finley, S Tongay
Room-Temperature Synthesis of 2D Janus Crystals and their Heterostructures Journal Article
In: Advanced Materials, vol. 32, no. 50, pp. 2006320, 2020, ISSN: 0935-9648.
@article{,
title = {Room-Temperature Synthesis of 2D Janus Crystals and their Heterostructures},
author = {D B Trivedi and G Turgut and Y Qin and M Y Sayyad and D Hajra and M Howell and L Liu and S Yang and N H Patoary and H Li and M M Petri\'{c} and M Meyer and M Kremser and M Barbone and G Soavi and A V Stier and K M\"{u}ller and S Yang and I S Esqueda and H Zhuang and J J Finley and S Tongay},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.202006320},
doi = {https://doi.org/10.1002/adma.202006320},
issn = {0935-9648},
year = {2020},
date = {2020-11-11},
journal = {Advanced Materials},
volume = {32},
number = {50},
pages = {2006320},
abstract = {Abstract Janus crystals represent an exciting class of 2D materials with different atomic species on their upper and lower facets. Theories have predicted that this symmetry breaking induces an electric field and leads to a wealth of novel properties, such as large Rashba spin\textendashorbit coupling and formation of strongly correlated electronic states. Monolayer MoSSe Janus crystals have been synthesized by two methods, via controlled sulfurization of monolayer MoSe2 and via plasma stripping followed thermal annealing of MoS2. However, the high processing temperatures prevent growth of other Janus materials and their heterostructures. Here, a room-temperature technique for the synthesis of a variety of Janus monolayers with high structural and optical quality is reported. This process involves low-energy reactive radical precursors, which enables selective removal and replacement of the uppermost chalcogen layer, thus transforming classical transition metal dichalcogenides into a Janus structure. The resulting materials show clear mixed character for their excitonic transitions, and more importantly, the presented room-temperature method enables the demonstration of first vertical and lateral heterojunctions of 2D Janus TMDs. The results present significant and pioneering advances in the synthesis of new classes of 2D materials, and pave the way for the creation of heterostructures from 2D Janus layers.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Janus crystals represent an exciting class of 2D materials with different atomic species on their upper and lower facets. Theories have predicted that this symmetry breaking induces an electric field and leads to a wealth of novel properties, such as large Rashba spin–orbit coupling and formation of strongly correlated electronic states. Monolayer MoSSe Janus crystals have been synthesized by two methods, via controlled sulfurization of monolayer MoSe2 and via plasma stripping followed thermal annealing of MoS2. However, the high processing temperatures prevent growth of other Janus materials and their heterostructures. Here, a room-temperature technique for the synthesis of a variety of Janus monolayers with high structural and optical quality is reported. This process involves low-energy reactive radical precursors, which enables selective removal and replacement of the uppermost chalcogen layer, thus transforming classical transition metal dichalcogenides into a Janus structure. The resulting materials show clear mixed character for their excitonic transitions, and more importantly, the presented room-temperature method enables the demonstration of first vertical and lateral heterojunctions of 2D Janus TMDs. The results present significant and pioneering advances in the synthesis of new classes of 2D materials, and pave the way for the creation of heterostructures from 2D Janus layers.
15.
Del F Giudice, J Becker, De C Rose, M Döblinger, D Ruhstorfer, L Suomenniemi, J Treu, H Riedl, J J Finley, G Koblmüller
Ultrathin catalyst-free InAs nanowires on silicon with distinct 1D sub-band transport properties Journal Article
In: Nanoscale, vol. 12, no. 42, pp. 21857-21868, 2020, ISSN: 2040-3364.
@article{,
title = {Ultrathin catalyst-free InAs nanowires on silicon with distinct 1D sub-band transport properties},
author = {Del F Giudice and J Becker and De C Rose and M D\"{o}blinger and D Ruhstorfer and L Suomenniemi and J Treu and H Riedl and J J Finley and G Koblm\"{u}ller},
url = {http://dx.doi.org/10.1039/D0NR05666A},
doi = {10.1039/D0NR05666A},
issn = {2040-3364},
year = {2020},
date = {2020-10-01},
journal = {Nanoscale},
volume = {12},
number = {42},
pages = {21857-21868},
abstract = {Ultrathin InAs nanowires (NW) with a one-dimensional (1D) sub-band structure are promising materials for advanced quantum-electronic devices, where dimensions in the sub-30 nm diameter limit together with post-CMOS integration scenarios on Si are much desired. Here, we demonstrate two site-selective synthesis methods that achieve epitaxial, high aspect ratio InAs NWs on Si with ultrathin diameters below 20 nm. The first approach exploits direct vapor\textendashsolid growth to tune the NW diameter by interwire spacing, mask opening size and growth time. The second scheme explores a unique reverse-reaction growth by which the sidewalls of InAs NWs are thermally decomposed under controlled arsenic flux and annealing time. Interesting kinetically limited dependencies between interwire spacing and thinning dynamics are found, yielding diameters as low as 12 nm for sparse NW arrays. We clearly verify the 1D sub-band structure in ultrathin NWs by pronounced conductance steps in low-temperature transport measurements using back-gated NW-field effect transistors. Correlated simulations reveal single- and double degenerate conductance steps, which highlight the rotational hexagonal symmetry and reproduce the experimental traces in the diffusive 1D transport limit. Modelling under the realistic back-gate configuration further evidences regimes that lead to asymmetric carrier distribution and breakdown of the degeneracy depending on the gate bias.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ultrathin InAs nanowires (NW) with a one-dimensional (1D) sub-band structure are promising materials for advanced quantum-electronic devices, where dimensions in the sub-30 nm diameter limit together with post-CMOS integration scenarios on Si are much desired. Here, we demonstrate two site-selective synthesis methods that achieve epitaxial, high aspect ratio InAs NWs on Si with ultrathin diameters below 20 nm. The first approach exploits direct vapor–solid growth to tune the NW diameter by interwire spacing, mask opening size and growth time. The second scheme explores a unique reverse-reaction growth by which the sidewalls of InAs NWs are thermally decomposed under controlled arsenic flux and annealing time. Interesting kinetically limited dependencies between interwire spacing and thinning dynamics are found, yielding diameters as low as 12 nm for sparse NW arrays. We clearly verify the 1D sub-band structure in ultrathin NWs by pronounced conductance steps in low-temperature transport measurements using back-gated NW-field effect transistors. Correlated simulations reveal single- and double degenerate conductance steps, which highlight the rotational hexagonal symmetry and reproduce the experimental traces in the diffusive 1D transport limit. Modelling under the realistic back-gate configuration further evidences regimes that lead to asymmetric carrier distribution and breakdown of the degeneracy depending on the gate bias.
14.
F Del Giudice, J Becker, C De Rose, M Döblinger, D Ruhstorfer, L Suomenniemi, J Treu, H Riedl, J J Finley, G Koblmüller
Ultrathin catalyst-free InAs nanowires on silicon with distinct 1D sub-band transport properties Journal Article
In: Nanoscale, vol. 12, no. 42, pp. 21857-21868, 2020, ISSN: 2040-3364.
@article{nokey,
title = {Ultrathin catalyst-free InAs nanowires on silicon with distinct 1D sub-band transport properties},
author = {F Del Giudice and J Becker and C De Rose and M D\"{o}blinger and D Ruhstorfer and L Suomenniemi and J Treu and H Riedl and J J Finley and G Koblm\"{u}ller},
url = {http://dx.doi.org/10.1039/D0NR05666A},
doi = {10.1039/D0NR05666A},
issn = {2040-3364},
year = {2020},
date = {2020-10-01},
journal = {Nanoscale},
volume = {12},
number = {42},
pages = {21857-21868},
abstract = {Ultrathin InAs nanowires (NW) with a one-dimensional (1D) sub-band structure are promising materials for advanced quantum-electronic devices, where dimensions in the sub-30 nm diameter limit together with post-CMOS integration scenarios on Si are much desired. Here, we demonstrate two site-selective synthesis methods that achieve epitaxial, high aspect ratio InAs NWs on Si with ultrathin diameters below 20 nm. The first approach exploits direct vapor\textendashsolid growth to tune the NW diameter by interwire spacing, mask opening size and growth time. The second scheme explores a unique reverse-reaction growth by which the sidewalls of InAs NWs are thermally decomposed under controlled arsenic flux and annealing time. Interesting kinetically limited dependencies between interwire spacing and thinning dynamics are found, yielding diameters as low as 12 nm for sparse NW arrays. We clearly verify the 1D sub-band structure in ultrathin NWs by pronounced conductance steps in low-temperature transport measurements using back-gated NW-field effect transistors. Correlated simulations reveal single- and double degenerate conductance steps, which highlight the rotational hexagonal symmetry and reproduce the experimental traces in the diffusive 1D transport limit. Modelling under the realistic back-gate configuration further evidences regimes that lead to asymmetric carrier distribution and breakdown of the degeneracy depending on the gate bias.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ultrathin InAs nanowires (NW) with a one-dimensional (1D) sub-band structure are promising materials for advanced quantum-electronic devices, where dimensions in the sub-30 nm diameter limit together with post-CMOS integration scenarios on Si are much desired. Here, we demonstrate two site-selective synthesis methods that achieve epitaxial, high aspect ratio InAs NWs on Si with ultrathin diameters below 20 nm. The first approach exploits direct vapor–solid growth to tune the NW diameter by interwire spacing, mask opening size and growth time. The second scheme explores a unique reverse-reaction growth by which the sidewalls of InAs NWs are thermally decomposed under controlled arsenic flux and annealing time. Interesting kinetically limited dependencies between interwire spacing and thinning dynamics are found, yielding diameters as low as 12 nm for sparse NW arrays. We clearly verify the 1D sub-band structure in ultrathin NWs by pronounced conductance steps in low-temperature transport measurements using back-gated NW-field effect transistors. Correlated simulations reveal single- and double degenerate conductance steps, which highlight the rotational hexagonal symmetry and reproduce the experimental traces in the diffusive 1D transport limit. Modelling under the realistic back-gate configuration further evidences regimes that lead to asymmetric carrier distribution and breakdown of the degeneracy depending on the gate bias.
13.
T Neumann, S Feldmann, P Moser, J Zerhoch, T Van De Goor, A Delhomme, T Winkler, J J Finley, C Faugeras, M S Brandt
Magnetic proximity effect on excitonic spin states in Mn-doped layered hybrid perovskites Journal Article
In: arXiv preprint arXiv:2009.13867, 2020.
@article{nokey,
title = {Magnetic proximity effect on excitonic spin states in Mn-doped layered hybrid perovskites},
author = {T Neumann and S Feldmann and P Moser and J Zerhoch and T Van De Goor and A Delhomme and T Winkler and J J Finley and C Faugeras and M S Brandt},
url = {https://arxiv.org/abs/2009.13867},
doi = {arXiv:2009.13867v1},
year = {2020},
date = {2020-09-29},
journal = {arXiv preprint arXiv:2009.13867},
abstract = {Materials combining the optoelectronic functionalities of semiconductors with control of the spin degree of freedom are highly sought after for the advancement of quantum technology devices. Here, we report the paramagnetic Ruddlesden-Popper hybrid perovskite Mn:(PEA)2PbI4 (PEA = phenethylammonium) in which the interaction of isolated Mn2+ ions with magnetically brightened excitons leads to circularly polarized photoluminescence. Using a combination of superconducting quantum interference device (SQUID) magnetometry and magneto-optical experiments, we find that the Brillouin-shaped polarization curve of the photoluminescence follows the magnetization of the material. This indicates coupling between localized manganese magnetic moments and exciton spins via a magnetic proximity effect. The saturation polarization of 15% at 4 K and 6 T indicates a highly imbalanced spin population and demonstrates that manganese doping enables efficient control of excitonic spin states in Ruddlesden-Popper perovskites. Our finding constitutes the first example of polarization control in magnetically doped hybrid perovskites and will stimulate research on this highly tuneable material platform that promises tailored interactions between magnetic moments and electronic states.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Materials combining the optoelectronic functionalities of semiconductors with control of the spin degree of freedom are highly sought after for the advancement of quantum technology devices. Here, we report the paramagnetic Ruddlesden-Popper hybrid perovskite Mn:(PEA)2PbI4 (PEA = phenethylammonium) in which the interaction of isolated Mn2+ ions with magnetically brightened excitons leads to circularly polarized photoluminescence. Using a combination of superconducting quantum interference device (SQUID) magnetometry and magneto-optical experiments, we find that the Brillouin-shaped polarization curve of the photoluminescence follows the magnetization of the material. This indicates coupling between localized manganese magnetic moments and exciton spins via a magnetic proximity effect. The saturation polarization of 15% at 4 K and 6 T indicates a highly imbalanced spin population and demonstrates that manganese doping enables efficient control of excitonic spin states in Ruddlesden-Popper perovskites. Our finding constitutes the first example of polarization control in magnetically doped hybrid perovskites and will stimulate research on this highly tuneable material platform that promises tailored interactions between magnetic moments and electronic states.
12.
K Barthelmi, J Klein, A Hötger, L Sigl, F Sigger, E Mitterreiter, S Rey, S Gyger, M Lorke, M Florian, F Jahnke, T Taniguchi, K Watanabe, V Zwiller, K D Jöns, U Wurstbauer, C Kastl, A Weber-Bargioni, J J Finley, K Müller, A W Holleitner
Atomistic defects as single-photon emitters in atomically thin MoS2 Journal Article
In: Applied Physics Letters, vol. 117, no. 7, pp. 070501, 2020, ISSN: 0003-6951.
@article{,
title = {Atomistic defects as single-photon emitters in atomically thin MoS2},
author = {K Barthelmi and J Klein and A H\"{o}tger and L Sigl and F Sigger and E Mitterreiter and S Rey and S Gyger and M Lorke and M Florian and F Jahnke and T Taniguchi and K Watanabe and V Zwiller and K D J\"{o}ns and U Wurstbauer and C Kastl and A Weber-Bargioni and J J Finley and K M\"{u}ller and A W Holleitner},
url = {https://doi.org/10.1063/5.0018557},
doi = {10.1063/5.0018557},
issn = {0003-6951},
year = {2020},
date = {2020-08-17},
journal = {Applied Physics Letters},
volume = {117},
number = {7},
pages = {070501},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
11.
M Kremser, M Brotons-Gisbert, J Knörzer, J Gückelhorn, M Meyer, M Barbone, A V Stier, B D Gerardot, K Müller, J J Finley
Discrete interactions between a few interlayer excitons trapped at a MoSe 2–WSe 2 heterointerface Journal Article
In: npj 2D Materials and Applications, vol. 4, no. 1, pp. 1-6, 2020, ISSN: 2397-7132.
@article{,
title = {Discrete interactions between a few interlayer excitons trapped at a MoSe 2\textendashWSe 2 heterointerface},
author = {M Kremser and M Brotons-Gisbert and J Kn\"{o}rzer and J G\"{u}ckelhorn and M Meyer and M Barbone and A V Stier and B D Gerardot and K M\"{u}ller and J J Finley},
issn = {2397-7132},
year = {2020},
date = {2020-06-24},
journal = {npj 2D Materials and Applications},
volume = {4},
number = {1},
pages = {1-6},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
10.
X Dong, A K Yetisen, H Tian, İ Güler, A V Stier, Z Li, M H Köhler, J Dong, M Jakobi, J J Finley, A W Koch
Line-Scan Hyperspectral Imaging Microscopy with Linear Unmixing for Automated Two-Dimensional Crystals Identification Journal Article
In: ACS Photonics, vol. 7, no. 5, pp. 1216-1225, 2020.
@article{,
title = {Line-Scan Hyperspectral Imaging Microscopy with Linear Unmixing for Automated Two-Dimensional Crystals Identification},
author = {X Dong and A K Yetisen and H Tian and \.{I} G\"{u}ler and A V Stier and Z Li and M H K\"{o}hler and J Dong and M Jakobi and J J Finley and A W Koch},
url = {https://doi.org/10.1021/acsphotonics.0c00050},
doi = {10.1021/acsphotonics.0c00050},
year = {2020},
date = {2020-04-23},
journal = {ACS Photonics},
volume = {7},
number = {5},
pages = {1216-1225},
abstract = {Two-dimensional (2D) materials exhibit unique optical properties when controlled to atomic thickness, and show large potential for applications in optoelectronics, photodetectors, and tunable excitonic devices. Current characterization techniques, including conventional optical microscopy, atomic force microscopy (AFM), and Raman spectroscopy are time-consuming and labor-intensive for studying large-scale samples. To realize the rapid identification of monolayer and few-layer crystals in the “haystack” of hundreds of flakes appearing in the exfoliation process, line-scan hyperspectral imaging microscopy combined with linear unmixing was developed to identify 2D molybdenum disulfide (MoS2) and hexagonal boron nitride (hBN) samples. A complete hyperspectral measurement and analysis, including single-band analysis, pixel-level spectral analysis and image classification was performed on MoS2 and hBN flakes with mono- and few-layer thickness. The characteristic spectra were extracted and analyzed via linear unmixing calculations to reconstruct the distribution images. The abundance maps showed the spatial distribution of these flakes with flake positions output, realizing an automatic identification of target flakes. This work shows a rapid and robust method for the determination of abundance maps of 2D flakes distributed over macroscopic areas.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Two-dimensional (2D) materials exhibit unique optical properties when controlled to atomic thickness, and show large potential for applications in optoelectronics, photodetectors, and tunable excitonic devices. Current characterization techniques, including conventional optical microscopy, atomic force microscopy (AFM), and Raman spectroscopy are time-consuming and labor-intensive for studying large-scale samples. To realize the rapid identification of monolayer and few-layer crystals in the “haystack” of hundreds of flakes appearing in the exfoliation process, line-scan hyperspectral imaging microscopy combined with linear unmixing was developed to identify 2D molybdenum disulfide (MoS2) and hexagonal boron nitride (hBN) samples. A complete hyperspectral measurement and analysis, including single-band analysis, pixel-level spectral analysis and image classification was performed on MoS2 and hBN flakes with mono- and few-layer thickness. The characteristic spectra were extracted and analyzed via linear unmixing calculations to reconstruct the distribution images. The abundance maps showed the spatial distribution of these flakes with flake positions output, realizing an automatic identification of target flakes. This work shows a rapid and robust method for the determination of abundance maps of 2D flakes distributed over macroscopic areas.
9.
D Ruhstorfer, S Mejia, M Ramsteiner, M Döblinger, H Riedl, J J Finley, G Koblmüller
Demonstration of n-type behavior in catalyst-free Si-doped GaAs nanowires grown by molecular beam epitaxy Journal Article
In: Applied Physics Letters, vol. 116, no. 5, pp. 052101, 2020.
@article{,
title = {Demonstration of n-type behavior in catalyst-free Si-doped GaAs nanowires grown by molecular beam epitaxy},
author = {D Ruhstorfer and S Mejia and M Ramsteiner and M D\"{o}blinger and H Riedl and J J Finley and G Koblm\"{u}ller},
url = {https://aip.scitation.org/doi/abs/10.1063/1.5134687},
doi = {10.1063/1.5134687},
year = {2020},
date = {2020-02-04},
journal = {Applied Physics Letters},
volume = {116},
number = {5},
pages = {052101},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
8.
J Klein, L Sigl, A Hötger, S Gyger, K Barthelmi, M Florian, A Kerelsky, E Mitterreiter, C Kastl, S Rey, T Taniguchi, K Watanabe, F Jahnke, V Zwiller, K Jöns, A Pasupathy, F Ross, K Müller, U Wurstbauer, J J Finley, A W Holleitner
Scalable single-photon sources in atomically thin MoS2 Journal Article
In: vol. 11471, 2020.
@article{nokey,
title = {Scalable single-photon sources in atomically thin MoS2},
author = {J Klein and L Sigl and A H\"{o}tger and S Gyger and K Barthelmi and M Florian and A Kerelsky and E Mitterreiter and C Kastl and S Rey and T Taniguchi and K Watanabe and F Jahnke and V Zwiller and K J\"{o}ns and A Pasupathy and F Ross and K M\"{u}ller and U Wurstbauer and J J Finley and A W Holleitner},
url = {https://doi.org/10.1117/12.2570472},
doi = {10.1117/12.2570472},
year = {2020},
date = {2020-01-01},
urldate = {2020-01-01},
volume = {11471},
publisher = {SPIE},
series = {SPIE Nanoscience + Engineering},
abstract = {2D materials offer a wide range of perspectives for hosting highly localized 0D states, e.g. vacancy defects, that offer great potential for integrated quantum photonic applications. Here, we create individual defects that act as our single-photon emitters by highly local He-ion irradiation in a monolayer MoS2 van der Waals heterostructure. The defects show anti-bunched light emission at a characteristic energy of ~ 1.75 eV. The emission is highly homogeneous and background free due to the hBN encapsulation with a creation yield of \> 70%. Spectroscopic investigation of individual single-photon emitters reveals a strongly asymmetric line shape resembling interaction with acoustic phonons in excellent agreement with an independent boson model. Moreover, emitters are spatially integrated and electrically controlled in field-switchable van der Waals devices. Our work firmly establishes 2D materials as a highly scalable material platform for integrated quantum photonics.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2D materials offer a wide range of perspectives for hosting highly localized 0D states, e.g. vacancy defects, that offer great potential for integrated quantum photonic applications. Here, we create individual defects that act as our single-photon emitters by highly local He-ion irradiation in a monolayer MoS2 van der Waals heterostructure. The defects show anti-bunched light emission at a characteristic energy of ~ 1.75 eV. The emission is highly homogeneous and background free due to the hBN encapsulation with a creation yield of > 70%. Spectroscopic investigation of individual single-photon emitters reveals a strongly asymmetric line shape resembling interaction with acoustic phonons in excellent agreement with an independent boson model. Moreover, emitters are spatially integrated and electrically controlled in field-switchable van der Waals devices. Our work firmly establishes 2D materials as a highly scalable material platform for integrated quantum photonics.
7.
J Klein, A Kerelsky, M Lorke, M Florian, F Sigger, J Kiemle, M C Reuter, T Taniguchi, K Watanabe, J J Finley, A N Pasupathy, A W Holleitner, F M Ross, U Wurstbauer
Impact of substrate induced band tail states on the electronic and optical properties of MoS2 Journal Article
In: Applied Physics Letters, vol. 115, no. 26, 2019, ISSN: 0003-6951.
@article{,
title = {Impact of substrate induced band tail states on the electronic and optical properties of MoS2},
author = {J Klein and A Kerelsky and M Lorke and M Florian and F Sigger and J Kiemle and M C Reuter and T Taniguchi and K Watanabe and J J Finley and A N Pasupathy and A W Holleitner and F M Ross and U Wurstbauer},
url = {\<Go to ISI\>://WOS:000505613600019},
doi = {10.1063/1.5131270},
issn = {0003-6951},
year = {2019},
date = {2019-12-30},
journal = {Applied Physics Letters},
volume = {115},
number = {26},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
6.
S Fust, A Faustmann, D J Carrad, J Bissinger, B Loitsch, M Döblinger, J Becker, G Abstreiter, J J Finley, G Koblmüller
Quantum-Confinement-Enhanced Thermoelectric Properties in Modulation-Doped GaAs–AlGaAs Core–Shell Nanowires Journal Article
In: Advanced Materials, vol. 32, no. 4, pp. 1905458, 2019, ISSN: 0935-9648.
@article{,
title = {Quantum-Confinement-Enhanced Thermoelectric Properties in Modulation-Doped GaAs\textendashAlGaAs Core\textendashShell Nanowires},
author = {S Fust and A Faustmann and D J Carrad and J Bissinger and B Loitsch and M D\"{o}blinger and J Becker and G Abstreiter and J J Finley and G Koblm\"{u}ller},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201905458},
doi = {10.1002/adma.201905458},
issn = {0935-9648},
year = {2019},
date = {2019-12-09},
journal = {Advanced Materials},
volume = {32},
number = {4},
pages = {1905458},
abstract = {Abstract Nanowires (NWs) hold great potential in advanced thermoelectrics due to their reduced dimensions and low-dimensional electronic character. However, unfavorable links between electrical and thermal conductivity in state-of-the-art unpassivated NWs have, so far, prevented the full exploitation of their distinct advantages. A promising model system for a surface-passivated one-dimensional (1D)-quantum confined NW thermoelectric is developed that enables simultaneously the observation of enhanced thermopower via quantum oscillations in the thermoelectric transport and a strong reduction in thermal conductivity induced by the core\textendashshell heterostructure. High-mobility modulation-doped GaAs/AlGaAs core\textendashshell NWs with thin (sub-40 nm) GaAs NW core channel are employed, where the electrical and thermoelectric transport is characterized on the same exact 1D-channel. 1D-sub-band transport at low temperature is verified by a discrete stepwise increase in the conductance, which coincided with strong oscillations in the corresponding Seebeck voltage that decay with increasing sub-band number. Peak Seebeck coefficients as high as ≈65\textendash85 µV K−1 are observed for the lowest sub-bands, resulting in equivalent thermopower of S2σ ≈ 60 µW m−1 K−2 and S2G ≈ 0.06 pW K−2 within a single sub-band. Remarkably, these core\textendashshell NW heterostructures also exhibit thermal conductivities as low as ≈3 W m−1 K−1, about one order of magnitude lower than state-of-the-art unpassivated GaAs NWs.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Nanowires (NWs) hold great potential in advanced thermoelectrics due to their reduced dimensions and low-dimensional electronic character. However, unfavorable links between electrical and thermal conductivity in state-of-the-art unpassivated NWs have, so far, prevented the full exploitation of their distinct advantages. A promising model system for a surface-passivated one-dimensional (1D)-quantum confined NW thermoelectric is developed that enables simultaneously the observation of enhanced thermopower via quantum oscillations in the thermoelectric transport and a strong reduction in thermal conductivity induced by the core–shell heterostructure. High-mobility modulation-doped GaAs/AlGaAs core–shell NWs with thin (sub-40 nm) GaAs NW core channel are employed, where the electrical and thermoelectric transport is characterized on the same exact 1D-channel. 1D-sub-band transport at low temperature is verified by a discrete stepwise increase in the conductance, which coincided with strong oscillations in the corresponding Seebeck voltage that decay with increasing sub-band number. Peak Seebeck coefficients as high as ≈65–85 µV K−1 are observed for the lowest sub-bands, resulting in equivalent thermopower of S2σ ≈ 60 µW m−1 K−2 and S2G ≈ 0.06 pW K−2 within a single sub-band. Remarkably, these core–shell NW heterostructures also exhibit thermal conductivities as low as ≈3 W m−1 K−1, about one order of magnitude lower than state-of-the-art unpassivated GaAs NWs.
5.
J Treu, X Xu, K Ott, K Saller, G Abstreiter, J J Finley, G Koblmüller
Optical absorption of composition-tunable InGaAs nanowire arrays Journal Article
In: Nanotechnology, vol. 30, no. 49, pp. 495703, 2019, ISSN: 0957-4484 1361-6528.
@article{,
title = {Optical absorption of composition-tunable InGaAs nanowire arrays},
author = {J Treu and X Xu and K Ott and K Saller and G Abstreiter and J J Finley and G Koblm\"{u}ller},
url = {http://dx.doi.org/10.1088/1361-6528/ab3ef7},
doi = {10.1088/1361-6528/ab3ef7},
issn = {0957-4484
1361-6528},
year = {2019},
date = {2019-09-20},
journal = {Nanotechnology},
volume = {30},
number = {49},
pages = {495703},
abstract = {InGaAs nanowire (NW) arrays have emerged as important active materials in future photovoltaic and photodetector applications, due to their excellent electronic properties and tunable band gap. Here, we report a systematic investigation of the optical absorption characteristics of composition-tunable vertical InGaAs NW arrays. Using finite-difference time-domain simulations we first study the effect of variable composition (Ga-molar fraction) and NW array geometry (NW diameter, period, fill factor) on the optical generation rate. NWs with typical diameters in the range of ∼100\textendash250 nm lead to generation rates higher than the equivalent bulk case for moderate fill factors (NW period of ∼0.3\textendash0.8 μm), while slightly smaller fill factors and increased diameters are required to maintain high generation rates at increased Ga-molar fraction. The optical absorption was further measured using spectrally resolved ultraviolet\textendashvisible-near-infrared (UV\textendashvis-NIR) spectroscopy on NW arrays transferred to transparent substrates. Interestingly, large variations in Ga-molar fraction (0 \< x(Ga) \< 0.5) have a negligible influence, while minute changes in NW diameter of less than ±20 nm affect the absorption spectra very strongly, leading to pronounced shifts in the peak absorption energies by more than ∼700 meV. These results clearly highlight the much larger sensitivity of the optical absorption behavior to geometric parameters rather than to variations in the electronic band gap of the underlying NW array.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
InGaAs nanowire (NW) arrays have emerged as important active materials in future photovoltaic and photodetector applications, due to their excellent electronic properties and tunable band gap. Here, we report a systematic investigation of the optical absorption characteristics of composition-tunable vertical InGaAs NW arrays. Using finite-difference time-domain simulations we first study the effect of variable composition (Ga-molar fraction) and NW array geometry (NW diameter, period, fill factor) on the optical generation rate. NWs with typical diameters in the range of ∼100–250 nm lead to generation rates higher than the equivalent bulk case for moderate fill factors (NW period of ∼0.3–0.8 μm), while slightly smaller fill factors and increased diameters are required to maintain high generation rates at increased Ga-molar fraction. The optical absorption was further measured using spectrally resolved ultraviolet–visible-near-infrared (UV–vis-NIR) spectroscopy on NW arrays transferred to transparent substrates. Interestingly, large variations in Ga-molar fraction (0 < x(Ga) < 0.5) have a negligible influence, while minute changes in NW diameter of less than ±20 nm affect the absorption spectra very strongly, leading to pronounced shifts in the peak absorption energies by more than ∼700 meV. These results clearly highlight the much larger sensitivity of the optical absorption behavior to geometric parameters rather than to variations in the electronic band gap of the underlying NW array.
4.
M Blauth, G Vest, S L Rosemary, M Prechtl, O Hartwig, M Jurgensen, M Kaniber, A V Stier, J J Finley
Ultracompact Photodetection in Atomically Thin MoSe2 Journal Article
In: Acs Photonics, vol. 6, no. 8, pp. 1902-1909, 2019, ISSN: 2330-4022.
@article{,
title = {Ultracompact Photodetection in Atomically Thin MoSe2},
author = {M Blauth and G Vest and S L Rosemary and M Prechtl and O Hartwig and M Jurgensen and M Kaniber and A V Stier and J J Finley},
url = {\<Go to ISI\>://WOS:000482545400012},
doi = {10.1021/acsphotonics.9b00785},
issn = {2330-4022},
year = {2019},
date = {2019-07-30},
journal = {Acs Photonics},
volume = {6},
number = {8},
pages = {1902-1909},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
3.
J Klein, M Lorke, M Florian, F Sigger, L Sigl, S Rey, J Wierzbowski, J Cerne, K Müller, E Mitterreiter, P Zimmermann, T Taniguchi, K Watanabe, U Wurstbauer, M Kaniber, M Knap, R Schmidt, J J Finley, A W Holleitner
Site-selectively generated photon emitters in monolayer MoS2 via local helium ion irradiation Journal Article
In: Nature Communications, vol. 10, no. 1, pp. 2755, 2019, ISSN: 2041-1723.
@article{,
title = {Site-selectively generated photon emitters in monolayer MoS2 via local helium ion irradiation},
author = {J Klein and M Lorke and M Florian and F Sigger and L Sigl and S Rey and J Wierzbowski and J Cerne and K M\"{u}ller and E Mitterreiter and P Zimmermann and T Taniguchi and K Watanabe and U Wurstbauer and M Kaniber and M Knap and R Schmidt and J J Finley and A W Holleitner},
url = {https://doi.org/10.1038/s41467-019-10632-z},
doi = {10.1038/s41467-019-10632-z},
issn = {2041-1723},
year = {2019},
date = {2019-06-21},
journal = {Nature Communications},
volume = {10},
number = {1},
pages = {2755},
abstract = {Quantum light sources in solid-state systems are of major interest as a basic ingredient for integrated quantum photonic technologies. The ability to tailor quantum emitters via site-selective defect engineering is essential for realizing scalable architectures. However, a major difficulty is that defects need to be controllably positioned within the material. Here, we overcome this challenge by controllably irradiating monolayer MoS2 using a sub-nm focused helium ion beam to deterministically create defects. Subsequent encapsulation of the ion exposed MoS2 flake with high-quality hBN reveals spectrally narrow emission lines that produce photons in the visible spectral range. Based on ab-initio calculations we interpret these emission lines as stemming from the recombination of highly localized electron\textendashhole complexes at defect states generated by the local helium ion exposure. Our approach to deterministically write optically active defect states in a single transition metal dichalcogenide layer provides a platform for realizing exotic many-body systems, including coupled single-photon sources and interacting exciton lattices that may allow the exploration of Hubbard physics.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Quantum light sources in solid-state systems are of major interest as a basic ingredient for integrated quantum photonic technologies. The ability to tailor quantum emitters via site-selective defect engineering is essential for realizing scalable architectures. However, a major difficulty is that defects need to be controllably positioned within the material. Here, we overcome this challenge by controllably irradiating monolayer MoS2 using a sub-nm focused helium ion beam to deterministically create defects. Subsequent encapsulation of the ion exposed MoS2 flake with high-quality hBN reveals spectrally narrow emission lines that produce photons in the visible spectral range. Based on ab-initio calculations we interpret these emission lines as stemming from the recombination of highly localized electron–hole complexes at defect states generated by the local helium ion exposure. Our approach to deterministically write optically active defect states in a single transition metal dichalcogenide layer provides a platform for realizing exotic many-body systems, including coupled single-photon sources and interacting exciton lattices that may allow the exploration of Hubbard physics.
2.
P Zimmermann, A Hötger, N Fernandez, A Nolinder, K Müller, J J Finley, A W Holleitner
Toward Plasmonic Tunnel Gaps for Nanoscale Photoemission Currents by On-Chip Laser Ablation Journal Article
In: Nano Letters, vol. 19, no. 2, pp. 1172-1178, 2019, ISSN: 1530-6984.
@article{,
title = {Toward Plasmonic Tunnel Gaps for Nanoscale Photoemission Currents by On-Chip Laser Ablation},
author = {P Zimmermann and A H\"{o}tger and N Fernandez and A Nolinder and K M\"{u}ller and J J Finley and A W Holleitner},
url = {https://doi.org/10.1021/acs.nanolett.8b04612},
doi = {10.1021/acs.nanolett.8b04612},
issn = {1530-6984},
year = {2019},
date = {2019-02-13},
journal = {Nano Letters},
volume = {19},
number = {2},
pages = {1172-1178},
abstract = {We demonstrate that prestructured metal nanogaps can be shaped on-chip to below 10 nm by femtosecond laser ablation. We explore the plasmonic properties and the nonlinear photocurrent characteristics of the formed tunnel junctions. The photocurrent can be tuned from multiphoton absorption toward the laser-induced strong-field tunneling regime in the nanogaps. We demonstrate that a unipolar ballistic electron current is achieved by designing the plasmonic junctions to be asymmetric, which allows ultrafast electronics on the nanometer scale.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We demonstrate that prestructured metal nanogaps can be shaped on-chip to below 10 nm by femtosecond laser ablation. We explore the plasmonic properties and the nonlinear photocurrent characteristics of the formed tunnel junctions. The photocurrent can be tuned from multiphoton absorption toward the laser-induced strong-field tunneling regime in the nanogaps. We demonstrate that a unipolar ballistic electron current is achieved by designing the plasmonic junctions to be asymmetric, which allows ultrafast electronics on the nanometer scale.
1.
P Zimmermann, A Hötger, N Fernandez, A Nolinder, K Müller, J J Finley, A W Holleitner
Toward Plasmonic Tunnel Gaps for Nanoscale Photoemission Currents by On-Chip Laser Ablation Journal Article
In: Nano Letters, vol. 19, no. 2, pp. 1172-1178, 2019, ISSN: 1530-6984.
@article{,
title = {Toward Plasmonic Tunnel Gaps for Nanoscale Photoemission Currents by On-Chip Laser Ablation},
author = {P Zimmermann and A H\"{o}tger and N Fernandez and A Nolinder and K M\"{u}ller and J J Finley and A W Holleitner},
url = {https://doi.org/10.1021/acs.nanolett.8b04612},
doi = {10.1021/acs.nanolett.8b04612},
issn = {1530-6984},
year = {2019},
date = {2019-02-13},
journal = {Nano Letters},
volume = {19},
number = {2},
pages = {1172-1178},
abstract = {We demonstrate that prestructured metal nanogaps can be shaped on-chip to below 10 nm by femtosecond laser ablation. We explore the plasmonic properties and the nonlinear photocurrent characteristics of the formed tunnel junctions. The photocurrent can be tuned from multiphoton absorption toward the laser-induced strong-field tunneling regime in the nanogaps. We demonstrate that a unipolar ballistic electron current is achieved by designing the plasmonic junctions to be asymmetric, which allows ultrafast electronics on the nanometer scale.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We demonstrate that prestructured metal nanogaps can be shaped on-chip to below 10 nm by femtosecond laser ablation. We explore the plasmonic properties and the nonlinear photocurrent characteristics of the formed tunnel junctions. The photocurrent can be tuned from multiphoton absorption toward the laser-induced strong-field tunneling regime in the nanogaps. We demonstrate that a unipolar ballistic electron current is achieved by designing the plasmonic junctions to be asymmetric, which allows ultrafast electronics on the nanometer scale.