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@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}

}

@article{nokey,

title = {Scanning probe spectroscopy of sulfur vacancies and MoS2 monolayers in side-contacted van der Waals heterostructures},

author = {K Nisi and J C Thomas and S Levashov and E Mitterreiter and T Taniguchi and K Watanabe and S Aloni and T R Kuykendall and J Eichhorn and A W Holleitner and A Weber-Bargioni and C Kastl},

url = {https://dx.doi.org/10.1088/2053-1583/ada046},

doi = {10.1088/2053-1583/ada046},

issn = {2053-1583},

year  = {2024},

date = {2024-12-30},

journal = {2D Materials},

volume = {12},

number = {1},

pages = {015023},

abstract = {We investigate the interplay between vertical tunneling and lateral transport phenomena in electrically contacted van der Waals heterostructures made from monolayer MoS2, hBN, and graphene. We compare data taken by low-temperature scanning tunneling spectroscopy to results from room-temperature conductive atomic force spectroscopy on monolayer MoS2 with sulfur vacancies and with varying hBN layers. We show that for thick hBN barrier layers, where tunneling currents into the conductive substrate are suppressed, a side-contact still enables addressing the defect states in the scanning tunneling microscopy via the lateral current flow. Few-layer hBN realizes an intermediate regime in which the competition between vertical tunneling and lateral transport needs to be considered. The latter is relevant for device structures with both a thin tunneling barrier and a side-contact to the semiconducting layers.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Ultrafast mid-infrared interferometric photocurrents in graphene-based two-terminal devices},

author = {N Pettinger and J Schmuck and X Zhou and S Loy and S Zherebtsov and C Kastl and A W Holleitner},

url = {https://doi.org/10.1063/5.0232394},

doi = {https://doi.org/10.1063/5.0232394},

issn = {0003-6951},

year  = {2024},

date = {2024-12-09},

journal = {Applied Physics Letters},

volume = {125},

number = {24},

abstract = {We demonstrate that graphene-based two-terminal devices allow autocorrelating femtosecond mid-infrared pulses with a pulse duration of about 100 fs in the wavelength regime of 5.5\textendash14 μm. The results suggest that the underlying ultrafast detection principle relies on an electric field dominated autocorrelation in combination with the optoelectronic dynamics at the metal\textendashgraphene interfaces. The demonstrated scheme excels because of the ease in nanofabrication of two-terminal graphene-based optoelectronic devices and their robustness.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Probing the Spatial Homogeneity of Exfoliated HfTe5 Films},

author = {M P Singh and Q Dong and G-F Chen and A W Holleitner and C Kastl},

url = {https://doi.org/10.1021/acsnano.4c02081},

doi = {10.1021/acsnano.4c02081},

issn = {1936-0851},

year  = {2024},

date = {2024-07-16},

journal = {ACS Nano},

volume = {18},

number = {28},

pages = {18327-18333},

abstract = {In van der Waals materials, external strain is an effective tool to manipulate and control electronic responses by changing the electronic bands upon lattice deformation. In particular, the band gap of the layered transition metal pentatelluride HfTe5 is sufficiently small to be inverted by subtle changes of the lattice parameters resulting in a strain-tunable topological phase transition. In that case, knowledge about the spatial homogeneity of electronic properties becomes crucial, especially for the microfabricated thin film circuits used in typical transport measurements. Here, we reveal the homogeneity of exfoliated HfTe5 thin films by spatially resolved Raman microscopy. Comparing the Raman spectra under applied external strain to unstrained bulk references, we pinpoint local variations of Raman signatures to inhomogeneous strain profiles in the sample. Importantly, our results demonstrate that microfabricated contacts can act as sources of significant inhomogeneities. To mitigate the impact of unintentional strain and its corresponding modifications of the electronic structure, careful Raman microscopy constitutes a valuable tool for quantifying the homogeneity of HfTe5 films and circuits fabricated thereof.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@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}

}

@article{nokey,

title = {Combining experiments on luminescent centres in hexagonal boron nitride with the polaron model and ab initio methods towards the identification of their microscopic origin},

author = {M Fischer and A Sajid and J Iles-Smith and A H\"{o}tger and D I Miakota and M K Svendsen and C Kastl and S Canulescu and S Xiao and M Wubs and K S Thygesen and A W Holleitner and N Stenger},

url = {http://dx.doi.org/10.1039/D3NR01511D},

doi = {10.1039/D3NR01511D},

issn = {2040-3364},

year  = {2023},

date = {2023-08-16},

journal = {Nanoscale},

volume = {15},

number = {34},

pages = {14215-14226},

abstract = {The two-dimensional material hexagonal boron nitride (hBN) hosts luminescent centres with emission energies of ∼2 eV which exhibit pronounced phonon sidebands. We investigate the microscopic origin of these luminescent centres by combining ab initio calculations with non-perturbative open quantum system theory to study the emission and absorption properties of 26 defect transitions. Comparing the calculated line shapes with experiments we narrow down the microscopic origin to three carbon-based defects: C2CB, C2CN, and VNCB. The theoretical method developed enables us to calculate so-called photoluminescence excitation (PLE) maps, which show excellent agreement with our experiments. The latter resolves higher-order phonon transitions, thereby confirming both the vibronic structure of the optical transition and the phonon-assisted excitation mechanism with a phonon energy ∼170 meV. We believe that the presented experiments and polaron-based method accurately describe luminescent centres in hBN and will help to identify their microscopic origin.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Space-charge limited and ultrafast dynamics in graphene-based nano-gaps},

author = {J Gr\"{o}bmeyer and P Zimmermann and B Huet and J A Robinson and A W Holleitner},

url = {https://doi.org/10.1063/5.0154152},

doi = {10.1063/5.0154152},

issn = {0003-6951},

year  = {2023},

date = {2023-07-03},

journal = {Applied Physics Letters},

volume = {123},

number = {1},

pages = {013504},

abstract = {We show that nano-gaps formed in graphene by utilizing a focused helium ion beam can act as ultrafast photoswitches. By temperature-dependent, time-integrated, and ultrafast photocurrent measurements, we demonstrate that the optoelectronic dynamics across such nano-gaps are dominated by a space-charge limited current in combination with the ultrafast dynamics of hot electrons. The demonstrated methodology allows the creation of ultrafast photoswitches with an amplification gain exceeding the ones as formed by pristine graphene.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@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}

}

@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}

}

@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}

}

@article{nokey,

title = {A Switchable One-Compound Diode},

author = {A Vogel and A Rabenbauer and P Deng and R Steib and T B\"{o}ger and W G Zeier and R Siegel and J Senker and D Daisenberger and K Nisi and A W Holleitner and J Venturini and T Nilges},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.202208698},

doi = {https://doi.org/10.1002/adma.202208698},

issn = {0935-9648},

year  = {2022},

date = {2022-10-25},

journal = {Advanced Materials},

volume = {n/a},

number = {n/a},

pages = {2208698},

abstract = {Abstract A diode or transistor requires the combination of p- and n-type semiconductors or at least the defined formation of such areas within a given compound. This is a prerequisite for any IT application, energy conversion technology, and electronic semiconductor devices. Since 2009, when the first pnp-switchable compound Ag10Te4Br3 was described, it is in principle possible to fabricate a diode from a single material without adjusting the semiconduction type by a defined doping level. After this discovery, a handful of other materials that are capable of reversibly switching between these two semiconducting stages was reported. In all cases, a structural phase transition accompanied by a dynamic change of charge carriers or a charge density wave (CDW) within certain substructures are responsible for this effect. Unfortunately, a certain feature hinders the application of this phenomenon in convenient devices, namely the pnp-switching temperature, which generally occurs well above room temperature, between 364 and 580 K. This effect is far removed from a suitable operation temperature at ambient conditions. Here, we report on Ag18Cu3Te11Cl3, a room temperature pnp-switching material, and the realization of the first single-material position-independent diode. The title compound shows the highest ever reported Seebeck coefficient drop that takes place within a few Kelvin at room temperature. Combined with its reasonably low thermal conductivity, this material offers great application potential within an easily accessible and applicable temperature window. Ag18Cu3Te11Cl3 and pnp-switching materials have the potential for applications and processes where diodes, transistors, or any defined charge separation with junction formation are utilized. This article is protected by copyright. All rights reserved},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Emitter-Optomechanical Interaction in high-Q hBN Nanocavities},

author = {C Qian and V Villafa\~{n}e and M Schalk and G V Astakhov and U Kentsch and M Helm and A H\"{o}tger and P Soubelet and A W Holleitner and A V Stier},

url = {https://arxiv.org/abs/2210.00150},

doi = {https://doi.org/10.48550/arXiv.2210.00150},

year  = {2022},

date = {2022-10-01},

journal = {arXiv preprint arXiv:2210.00150},

abstract = {We investigate the interaction between optically excited charged boron vacancies V−B, localized photonic modes of ultra-high-Q (∼105) nanocavities and local vibronic modes. V−B is a color center for which phonon-induced processes generally dominate the emission. A pronounced asymmetry is observed in the emission spectrum for cavities in which V−B centers have been generated by N+ irradiation. Similar asymmetries are not observed for systems that do not contain V−B centers. To explain our findings, we model the system as phonon-induced light-matter coupling with multi-partite interplay between the electronic transition, cavity photons and local vibronic modes. Good agreement is obtained between experiment and theory. Our results indicate that the multi-partite interplay arises during the V−B emission process, illustrating that it is phonon-induced, rather than being caused by thermal population of vibronic modes. The multi-modal couplings between various photonic (V−B emission, cavity nanophotonic) and vibronic (V−B phonons, cavity nanomechanical) modes provide novel method to interface spin, photons and phonons in condensed matter systems.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Defect-Engineered Magnetic Field Dependent Optoelectronics of Vanadium Doped Tungsten Diselenide Monolayers},

author = {K Nisi and J Kiemle and L Powalla and A Scavuzzo and T D Nguyen and T Taniguchi and K Watanabe and D L Duong and M Burghard and A W Holleitner and C Kastl},

url = {https://doi.org/10.1002/adom.202102711},

doi = {https://doi.org/10.1002/adom.202102711},

issn = {2195-1071},

year  = {2022},

date = {2022-09-01},

journal = {Advanced Optical Materials},

volume = {10},

number = {17},

pages = {2102711},

abstract = {Abstract The ability to dope transition metal dichalcogenides such as tungsten diselenide (WSe2) with magnetic transition metal atoms in a controlled manner has motivated intense research with the aim of generating dilute magnetic semiconductors. In this work, semiconducting WSe2 monolayers, substitutionally doped with vanadium atoms, are investigated using low-temperature luminescence and optoelectronic spectroscopy. V-dopants lead to a p-type doping character and an impurity-related emission ≈160 meV below the neutral exciton, both of which scale with the nominal percentage of V-dopants. Measurements using field-effect devices of 0.3% V-doped WSe2 demonstrate bipolar carrier tunability. The doped monolayers display a clear magnetic hysteresis in transport measurements both under illumination and without illumination, whereas the valley polarization of the excitons reveals a nonlinear g-factor without a magnetic hysteresis within the experimental uncertainty. Hence, this work on V-doped WSe2 provides crucial insights concerning suitable characterization methods on magnetic properties of doped 2D materials.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Gate-Tunable Helical Currents in Commensurate Topological Insulator/Graphene Heterostructures},

author = {J Kiemle and L Powalla and K Polyudov and L Gulati and M Singh and A W Holleitner and M Burghard and C Kastl},

url = {https://doi.org/10.1021/acsnano.2c03370},

doi = {10.1021/acsnano.2c03370},

issn = {1936-0851},

year  = {2022},

date = {2022-08-23},

journal = {ACS Nano},

volume = {16},

number = {8},

pages = {12338-12344},

abstract = {van der Waals heterostructures made from graphene and three-dimensional topological insulators promise very high electron mobilities, a nontrivial spin texture, and a gate-tunability of electronic properties. Such a combination of advantageous electronic characteristics can only be achieved through proximity effects in heterostructures, as graphene lacks a large enough spin\textendashorbit interaction. In turn, the heterostructures are promising candidates for all-electrical control of proximity-induced spin phenomena. Here, we explore epitaxially grown interfaces between graphene and the lattice-matched topological insulator Bi2Te2Se. For this heterostructure, spin\textendashorbit coupling proximity has been predicted to impart an anisotropic and electronically tunable spin texture. Polarization-resolved second-harmonic generation, Raman spectroscopy, and time-resolved magneto-optic Kerr microscopy are combined to demonstrate that the atomic interfaces align in a commensurate symmetry with characteristic interlayer vibrations. By polarization-resolved photocurrent measurements, we find a circular photogalvanic effect which is drastically enhanced at the Dirac point of the proximitized graphene. We attribute the peculiar gate-tunability to the proximity-induced interfacial spin structure, which could be exploited for, e.g., spin filters.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Spectroscopic imaging ellipsometry of two-dimensional TMDC heterostructures},

author = {F Sigger and H Lambers and K Nisi and J Klein and N Saigal and A W Holleitner and U Wurstbauer},

url = {https://doi.org/10.1063/5.0109189},

doi = {10.1063/5.0109189},

issn = {0003-6951},

year  = {2022},

date = {2022-08-15},

journal = {Applied Physics Letters},

volume = {121},

number = {7},

pages = {071102},

abstract = {Semiconducting two-dimensional materials and their heterostructures gained a lot of interest for applications as well as fundamental studies due to their rich optical properties. Assembly in van der Waals heterostacks can significantly alter the intrinsic optical properties as well as the wavelength-dependent absorption and emission efficiencies, making a direct comparison of, e.g., photoluminescence intensities difficult. Here, we determine the dielectric function for the prototypical MoSe2/WSe2 heterobilayer and their individual layers. Apart from a redshift of 18\textendash44 meV of the energetically lowest interband transitions, we find that for larger energies, the dielectric function can only be described by treating the van der Waals heterobilayer as a new artificial homobilayer crystal rather than a stack of individual layers. The determined dielectric functions are applied to calculate the Michelson contrast of the individual layers and the bilayer in dependence of the oxide thickness of often used Si/SiO2 substrates. Our results highlight the need to consider the altered dielectric functions impacting the Michelson interference in the interpretation of intensities in optical measurements such as Raman scattering or photoluminescence.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Thickness and defect dependent electronic, optical and thermoelectric features of WTe2},

author = {I Ozdemir and A W Holleitner and C Kastl and O \"{U} Akt\"{u}rk},

url = {https://doi.org/10.1038/s41598-022-16899-5},

doi = {10.1038/s41598-022-16899-5},

issn = {2045-2322},

year  = {2022},

date = {2022-07-18},

journal = {Scientific Reports},

volume = {12},

number = {1},

pages = {12756},

abstract = {Transition metal dichalcogenides (TMDs) receive significant attention due to their outstanding electronic and optical properties. In this study, we investigate the electronic, optical, and thermoelectric properties of single and few layer $$hbox WTe_2$$in detail utilizing first-principles methods based on the density functional theory (DFT). Within the scope of both PBE and HSE06 including spin orbit coupling (SOC), the simulations predict the electronic band gap values to decrease as the number of layers increases. Moreover, spin-polarized DFT calculations combined with the semi-classical Boltzmann transport theory are applied to estimate the anisotropic thermoelectric power factor (Seebeck coefficient, S) for $$hbox WTe_2$$in both the monolayer and multilayer limit, and S is obtained below the optimal value for practical applications. The optical absorbance of $$hbox WTe_2$$monolayer is obtained to be slightly less than the values reported in literature for 2H TMD monolayers of $$hbox MoS_2$$, $$hbox MoSe_2$$, and $$hbox WS_2$$. Furthermore, we simulate the impact of defects, such as vacancy, antisite and substitution defects, on the electronic, optical and thermoelectric properties of monolayer $$hbox WTe_2$$. Particularly, the Te-$$hbox O_2$$substitution defect in parallel orientation yields negative formation energy, indicating that the relevant defect may form spontaneously under relevant experimental conditions. We reveal that the electronic band structure of $$hbox WTe_2$$monolayer is significantly influenced by the presence of the considered defects. According to the calculated band gap values, a lowering of the conduction band minimum gives rise to metallic characteristics to the structure for the single Te(1) vacancy, a diagonal Te line defect, and the Te(1)-$$hbox O_2$$substitution, while the other investigated defects cause an opening of a small positive band gap at the Fermi level. Consequently, the real ($$varepsilon _1(\omega )$$) and imaginary ($$varepsilon _2(\omega )$$) parts of the dielectric constant at low frequencies are very sensitive to the applied defects, whereas we find that the absorbance (A) at optical frequencies is less significantly affected. We also predict that certain point defects can enhance the otherwise moderate value of S in pristine $$hbox WTe_2$$to values relevant for thermoelectric applications. The described $$hbox WTe_2$$monolayers, as functionalized with the considered defects, offer the possibility to be applied in optical, electronic, and thermoelectric devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@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}

}

@article{nokey,

title = {Berry curvature-induced local spin polarisation in gated graphene/WTe(2) heterostructures},

author = {L Powalla and J Kiemle and E J K\"{o}nig and A P Schnyder and J Knolle and K Kern and A W Holleitner and C Kastl and M Burghard},

doi = {10.1038/s41467-022-30744-3},

issn = {2041-1723},

year  = {2022},

date = {2022-06-07},

urldate = {2022-06-07},

journal = {Nat Commun},

volume = {13},

number = {1},

pages = {3152},

abstract = {Experimental control of local spin-charge interconversion is of primary interest for spintronics. Van der Waals (vdW) heterostructures combining graphene with a strongly spin-orbit coupled two-dimensional (2D) material enable such functionality by design. Electric spin valve experiments have thus far provided global information on such devices, while leaving the local interplay between symmetry breaking, charge flow across the heterointerface and aspects of topology unexplored. Here, we probe the gate-tunable local spin polarisation in current-driven graphene/WTe(2) heterostructures through magneto-optical Kerr microscopy. Even for a nominal in-plane transport, substantial out-of-plane spin accumulation is induced by a corresponding out-of-plane current flow. We present a theoretical model which fully explains the gate- and bias-dependent onset and spatial distribution of the intense Kerr signal as a result of a non-linear anomalous Hall effect in the heterostructure, which is enabled by its reduced point group symmetry. Our findings unravel the potential of 2D heterostructure engineering for harnessing topological phenomena for spintronics, and constitute an important step toward nanoscale, electrical spin control.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@article{nokey,

title = {Single-photon emitters in layered van der Waals materials},

author = {S Michaelis De Vasconcellos and D Wigger and U Wurstbauer and A W Holleitner and R Bratschitsch and T Kuhn},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/pssb.202100566},

doi = {https://doi.org/10.1002/pssb.202100566},

issn = {0370-1972},

year  = {2022},

date = {2022-01-28},

journal = {physica status solidi (b)},

volume = {n/a},

number = {n/a},

abstract = {Single-photon emitters have recently been discovered in various atomically thin materials. Their properties, controllability, and the possibility of their monolithic integration in electronic and photonic device structures makes them attractive candidates for a wide range of applications in quantum information and communication, and also in other fields of physics and technology. In this review article an overview of single-photon emitters in layered van der Waals materials and their physical properties is given, theoretical concepts for the modeling of their level structure and their coupling to phonons are presented, and techniques for the creation and localization of these emitters in the host material are described. Perspectives for their application in various fields, such as their coupling to photonic resonators and waveguides, their control by external electric fields or strain, and their integration in optomechanical devices are discussed. Finally, functionalities relying on properties beyond single-photon emission are briefly addressed. This article is protected by copyright. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Optical dipole orientation of interlayer excitons in MoSe2-WSe2 heterostacks},

author = {L Sigl and M Troue and M Katzer and M Selig and F Sigger and J Kiemle and M Brotons-Gisbert and K Watanabe and T Taniguchi and B D Gerardot and A Knorr and U Wurstbauer and A W Holleitner},

url = {https://link.aps.org/doi/10.1103/PhysRevB.105.035417},

doi = {10.1103/PhysRevB.105.035417},

year  = {2022},

date = {2022-01-14},

urldate = {2022-01-14},

journal = {Physical Review B},

volume = {105},

number = {3},

pages = {035417},

abstract = {We report on the far-field photoluminescence intensity distribution of interlayer excitons in 

MoSe2WSe2 heterostacks as measured by back focal plane imaging in the temperature range between 1.7 and 20 K. By comparing the data with an analytical model describing the dipolar emission pattern in a dielectric environment, we are able to obtain the relative contributions of the in- and out-of-plane transition dipole moments associated to the interlayer exciton photon emission. We determine the transition dipole moments for all observed interlayer exciton transitions to be (99±1)% in plane for R- and H-type stacking, independent of the excitation power and therefore the density of the exciton ensemble in the experimentally examined range. Finally, we discuss the limitations of the presented measurement technique to observe correlation effects in exciton ensembles.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {SnBrP-A SnIP-type representative in the Sn−Br−P system},

author = {F Reiter and M Pielmeier and A Vogel and C Jandl and M Plodinec and C Rohner and T Lunkenbein and K Nisi and A W Holleitner and T Nilges},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/zaac.202100347},

doi = {https://doi.org/10.1002/zaac.202100347},

issn = {0044-2313},

year  = {2022},

date = {2022-01-07},

urldate = {2022-01-07},

journal = {Zeitschrift f\"{u}r anorganische und allgemeine Chemie},

volume = {n/a},

number = {n/a},

pages = {e202100347},

abstract = {Abstract One-dimensional semiconductors are interesting materials due to their unique structural features and anisotropy, which grant them intriguing optical, dielectric and mechanical properties. In this work, we report on SnBrP, a lighter homologue of the first inorganic double helix compound SnIP. This class of compounds is characterized by intriguing mechanical and electronic properties, featuring a high flexibility without modulation of physical properties. Semiconducting SnBrP can be synthesized from red phosphorus, tin and tin(II)bromide at elevated temperatures and crystallizes as red-orange, cleavable needles. Raman measurements pointed towards a double helical building unit in SnBrP, showing similarities to the SnIP structure. After taking PL measurements, HR-TEM, and quantum chemical calculations into account, we were able to propose a sense full structure model for SnBrP.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@article{nokey,

title = {Trions in MoS2 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},

url = {https://arxiv.org/abs/2109.06281},

doi = {arXiv:2109.06281v1},

year  = {2021},

date = {2021-09-13},

journal = {arXiv preprint arXiv:2109.06281},

abstract = {We report magneto-photoluminescence spectroscopy of gated MoS2 monolayers in high magnetic fields to 28 T. At B = 0T and electron density ns∼1012cm−2, we observe three trion resonances that cannot be explained within a single-particle picture. Employing ab initio calculations that take into account three-particle correlation effects as well as local and non-local electron-hole exchange interaction, we identify those features as quantum superpositions of inter- and intravalley spin states. We experimentally investigate the mixed character of the trion wave function via the filling factor dependent valley Zeeman shift in positive and negative magnetic fields. Our results highlight the importance of exchange interactions for exciton physics in monolayer MoS2 and provide new insights into the microscopic understanding of trion physics in 2D multi-valley semiconductors for low excess carrier densities.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@article{,

title = {Ultrafast hot carrier relaxation in silicon monitored by phase-resolved transient absorption spectroscopy},

author = {M W\"{o}rle and A W Holleitner and R Kienberger and H Iglev},

year  = {2021},

date = {2021-01-05},

journal = {arXiv preprint arXiv:2101.01439},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Photophysics and Electronic Structure of Lateral Graphene/MoS2 and Metal/MoS2 Junctions},

author = {S Subramanian and Q T Campbell and S K Moser and J Kiemle and P Zimmermann and P Seifert and F Sigger and D Sharma and H Al-Sadeg and M Labella and D Waters and R M Feenstra and R J Koch and C Jozwiak and A Bostwick and E Rotenberg and I Dabo and A W Holleitner and T E Beechem and U Wurstbauer and J A Robinson},

url = {https://doi.org/10.1021/acsnano.0c02527},

doi = {10.1021/acsnano.0c02527},

issn = {1936-0851},

year  = {2020},

date = {2020-11-16},

journal = {ACS Nano},

abstract = {Integration of semiconducting transition metal dichalcogenides (TMDs) into functional optoelectronic circuitries requires an understanding of the charge transfer across the interface between the TMD and the contacting material. Here, we use spatially resolved photocurrent microscopy to demonstrate electronic uniformity at the epitaxial graphene/molybdenum disulfide (EG/MoS2) interface. A 10× larger photocurrent is extracted at the EG/MoS2 interface when compared to the metal (Ti/Au)/MoS2 interface. This is supported by semi-local density functional theory (DFT), which predicts the Schottky barrier at the EG/MoS2 interface to be ∼2× lower than that at Ti/MoS2. We provide a direct visualization of a 2D material Schottky barrier through combination of angle-resolved photoemission spectroscopy with spatial resolution selected to be ∼300 nm (nano-ARPES) and DFT calculations. A bending of ∼500 meV over a length scale of ∼2\textendash3 μm in the valence band maximum of MoS2 is observed via nano-ARPES. We explicate a correlation between experimental demonstration and theoretical predictions of barriers at graphene/TMD interfaces. Spatially resolved photocurrent mapping allows for directly visualizing the uniformity of built-in electric fields at heterostructure interfaces, providing a guide for microscopic engineering of charge transport across heterointerfaces. This simple probe-based technique also speaks directly to the 2D synthesis community to elucidate electronic uniformity at domain boundaries alongside morphological uniformity over large areas.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Photophysics and Electronic Structure of Lateral Graphene/MoS2 and Metal/MoS2 Junctions},

author = {S Subramanian and Q T Campbell and S K Moser and J Kiemle and P Zimmermann and P Seifert and F Sigger and D Sharma and H Al-Sadeg and M Labella and D Waters and R M Feenstra and R J Koch and C Jozwiak and A Bostwick and E Rotenberg and I Dabo and A W Holleitner and T E Beechem and U Wurstbauer and J A Robinson},

url = {https://doi.org/10.1021/acsnano.0c02527},

doi = {10.1021/acsnano.0c02527},

issn = {1936-0851},

year  = {2020},

date = {2020-11-16},

journal = {ACS Nano},

volume = {14},

number = {12},

pages = {16663-16671},

abstract = {Integration of semiconducting transition metal dichalcogenides (TMDs) into functional optoelectronic circuitries requires an understanding of the charge transfer across the interface between the TMD and the contacting material. Here, we use spatially resolved photocurrent microscopy to demonstrate electronic uniformity at the epitaxial graphene/molybdenum disulfide (EG/MoS2) interface. A 10× larger photocurrent is extracted at the EG/MoS2 interface when compared to the metal (Ti/Au)/MoS2 interface. This is supported by semi-local density functional theory (DFT), which predicts the Schottky barrier at the EG/MoS2 interface to be ∼2× lower than that at Ti/MoS2. We provide a direct visualization of a 2D material Schottky barrier through combination of angle-resolved photoemission spectroscopy with spatial resolution selected to be ∼300 nm (nano-ARPES) and DFT calculations. A bending of ∼500 meV over a length scale of ∼2\textendash3 μm in the valence band maximum of MoS2 is observed via nano-ARPES. We explicate a correlation between experimental demonstration and theoretical predictions of barriers at graphene/TMD interfaces. Spatially resolved photocurrent mapping allows for directly visualizing the uniformity of built-in electric fields at heterostructure interfaces, providing a guide for microscopic engineering of charge transport across heterointerfaces. This simple probe-based technique also speaks directly to the 2D synthesis community to elucidate electronic uniformity at domain boundaries alongside morphological uniformity over large areas.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Light\textendashMatter Interaction in Quantum Confined 2D Polar Metals},

author = {K Nisi and S Subramanian and W He and K A Ulman and H El-Sherif and F Sigger and M Lassauni\`{e}re and M T Wetherington and N Briggs and J Gray and A W Holleitner and N Bassim and S Y Quek and J A Robinson and U Wurstbauer},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202005977},

doi = {https://doi.org/10.1002/adfm.202005977},

issn = {1616-301X},

year  = {2020},

date = {2020-10-15},

urldate = {2020-10-15},

journal = {Advanced Functional Materials},

volume = {n/a},

number = {n/a},

pages = {2005977},

abstract = {Abstract This work is a systematic experimental and theoretical study of the in-plane dielectric functions of 2D gallium and indium films consisting of two or three atomic metal layers confined between silicon carbide and graphene with a corresponding bonding gradient from covalent to metallic to van der Waals type. k-space resolved free electron and bound electron contributions to the optical response are identified, with the latter pointing towards the existence of thickness dependent quantum confinement phenomena. The resonance energies in the dielectric functions and the observed epsilon near-zero behavior in the near infrared to visible spectral range, are dependent on the number of atomic metal layers and properties of the metal involved. A model-based spectroscopic ellipsometry approach is used to estimate the number of atomic metal layers, providing a convenient route over expensive invasive characterization techniques. A strong thickness and metal choice dependence of the light\textendashmatter interaction makes these half van der Waals 2D polar metals attractive for quantum engineered metal films, tunable (quantum-)plasmonics and nano-photonics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@article{nokey,

title = {Quantized many-body spin-valley textures in charge tunable monolayer MoS2},

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},

url = {https://www.researchgate.net/profile/Andreas-Stier/publication/343304456_Quantized_many-body_spin-valley_textures_in_charge_tunable_monolayer_MoS_2/links/5f226a5ca6fdcccc439945ae/Quantized-many-body-spin-valley-textures-in-charge-tunable-monolayer-MoS-2.pdf},

year  = {2020},

date = {2020-07-28},

journal = {arXiv preprint arXiv:2007.14441},

abstract = {We explore the many-body interaction of neutral, positively and negatively charged electron-hole pairs in a MoS2 monolayer with the distinct spin and valley textures of resident charges via density dependent high field magneto-optical spectroscopy. For the neutral exciton we unexpectedly observe nonlinear valley Zeeman effects, which we explain by dipolar spin-interactions of the exciton with the spin and valley polarized Fermi sea. At electron densities below 4·1012cm−2 we observe quantum oscillations in the photoluminescence of the intravalley trion as well as a Landau level occupation dependent non-uniform Zeeman shifts from which we determine both effective electron and hole masses. By increasing the local charge density to a situation where the Fermi energy dominates over the other relevant energy scales in the system, the magneto-optical response becomes dependent on the occupation of the fully spin-polarized Landau levels in both K/K0 valleys producing magnetooptical signatures of a many-body state. Our experiments unequivocally demonstrate that the exciton in monolayer semiconductors is a single particle boson only close to charge neutrality and that it smoothly transitions into a polaronic state with a spin-valley flavour that is defined by the local Landau level quantized spin and valley texture away from charge neutrality.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Atomistic Positioning of Defects in Helium Ion Treated Single-Layer MoS2},

author = {E Mitterreiter and B Schuler and K A Cochrane and U Wurstbauer and A Weber-Bargioni and C Kastl and A W Holleitner},

url = {\<Go to ISI\>://WOS:000541691200049},

doi = {10.1021/acs.nanolett.0c01222},

issn = {1530-6984},

year  = {2020},

date = {2020-06-10},

journal = {Nano Letters},

volume = {20},

number = {6},

pages = {4437-4444},

abstract = {Structuring materials with atomic precision is the ultimate goal of nanotechnology and is becoming increasingly relevant as an enabling technology for quantum electronics/spintronics and quantum photonics. Here, we create atomic defects in monolayer MoS2 by helium ion (He-ion) beam lithography with a spatial fidelity approaching the single-atom limit in all three dimensions. Using low-temperature scanning tunneling microscopy (STM), we confirm the formation of individual point defects in MoS2 upon He-ion bombardment and show that defects are generated within 9 nm of the incident helium ions. Atom-specific sputtering yields are determined by analyzing the type and occurrence of defects observed in high-resolution STM images and compared with with Monte Carlo simulations. Both theory and experiment indicate that the He-ion bombardment predominantly generates sulfur vacancies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Control of the orbital character of indirect excitons in MoS2/WS2 heterobilayers},

author = {J Kiemle and F Sigger and M Lorke and B Miller and K Watanabe and T Taniguchi and A W Holleitner and U Wurstbauer},

url = {https://link.aps.org/doi/10.1103/PhysRevB.101.121404},

doi = {10.1103/PhysRevB.101.121404},

year  = {2020},

date = {2020-03-18},

journal = {Physical Review B},

volume = {101},

number = {12},

pages = {121404},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {On-site tuning of the carrier lifetime in silicon for on-chip THz circuits using a focused beam of helium ions},

author = {P Zimmermann and A W Holleitner},

url = {https://doi.org/10.1063/1.5143421},

doi = {10.1063/1.5143421},

issn = {0003-6951},

year  = {2020},

date = {2020-02-18},

journal = {Applied Physics Letters},

volume = {116},

number = {7},

pages = {073501},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@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}

}

@article{,

title = {The fast and the furious: Ultrafast hot electrons in plasmonic metastructures. Size and structure matter},

author = {L V Besteiro and P Yu and Z M Wang and A W Holleitner and G V Hartland and G P Wiederrecht and A O Govorov},

url = {\<Go to ISI\>://WOS:000482526300011},

doi = {10.1016/j.nantod.2019.05.006},

issn = {1748-0132},

year  = {2019},

date = {2019-07-18},

journal = {Nano Today},

volume = {27},

pages = {120-145},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {In-situ visualization of hydrogen evolution sites on helium ion treated molybdenum dichalcogenides under reaction conditions},

author = {E Mitterreiter and Y Liang and M Golibrzuch and D Mclaughlin and C Csoklich and J D Bartl and A W Holleitner and U Wurstbauer and A S Bandarenka},

url = {https://doi.org/10.1038/s41699-019-0107-5},

doi = {10.1038/s41699-019-0107-5},

issn = {2397-7132},

year  = {2019},

date = {2019-07-15},

journal = {npj 2D Materials and Applications},

volume = {3},

number = {1},

pages = {25},

abstract = {Nanostructured 2D transition metal dichalcogenides play an increasingly important role in heterogeneous catalysis. These materials are abundant (co-)catalysts with tunable properties to catalyze a number of key reactions related to energy provision, for instance the hydrogen evolution reaction (HER). It is vital to understand which surface sites are active in order to maximize their number and to improve the overall (photo-)catalytic behavior of those materials. Here, we visualize these active sites under HER conditions at the surface of molybdenum dichalcogenides (MoX2, X = Se, S) with lateral resolution on the nanometer scale by means of electrochemical scanning tunneling microscopy. The edges of single MoX2 flakes show high catalytic activity, whereas their terraces are inactive. We demonstrate how the inert basal planes of these materials can be activated towards the HER with the help of a focused beam of a He-ion microscope. Our findings demonstrate that the He-ion induced defects contribute at lower overpotentials to the HER, while the activity of the edges exceeds the activity of the basal defects for sufficiently high overpotentials. Given the lithographic resolution of the helium ion microscope, our results show the possibility to generate active sites in transition metal dichalcogenides with a spatial resolution below a few nanometers.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@article{,

title = {Tuning the Fr\"{o}hlich exciton-phonon scattering in monolayer MoS2},

author = {B Miller and J Lindlau and M Bommert and A Neumann and H Yamaguchi and A W Holleitner and A H\"{o}gele and U Wurstbauer},

url = {https://doi.org/10.1038/s41467-019-08764-3},

doi = {10.1038/s41467-019-08764-3},

issn = {2041-1723},

year  = {2019},

date = {2019-02-18},

journal = {Nature Communications},

volume = {10},

number = {1},

pages = {807},

abstract = {Charge carriers in semiconducting transition metal dichalcogenides possess a valley degree of freedom that allows for optoelectronic applications based on the momentum of excitons. At elevated temperatures, scattering by phonons limits valley polarization, making a detailed knowledge about strength and nature of the interaction of excitons with phonons essential. In this work, we directly access exciton-phonon coupling in charge tunable single layer MoS2 devices by polarization resolved Raman spectroscopy. We observe a strong defect mediated coupling between the long-range oscillating electric field induced by the longitudinal optical phonon in the dipolar medium and the exciton. This so-called Fr\"{o}hlich exciton phonon interaction is suppressed by doping. The suppression correlates with a distinct increase of the degree of valley polarization up to 20% even at elevated temperatures of 220 K. Our result demonstrates a promising strategy to increase the degree of valley polarization towards room temperature valleytronic applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@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}

}

@article{,

title = {Top-Down Synthesis of Nanostructured Platinum\textendashLanthanide Alloy Oxygen Reduction Reaction Catalysts: PtxPr/C as an Example},

author = {J Fichtner and B Garlyyev and S Watzele and H A El-Sayed and J N Schw\"{a}mmlein and W-J Li and F M Maillard and L Dubau and J Michali\v{c}ka and J M Macak and A W Holleitner and A S Bandarenka},

url = {https://doi.org/10.1021/acsami.8b20174},

doi = {10.1021/acsami.8b20174},

issn = {1944-8244},

year  = {2019},

date = {2019-02-06},

journal = {ACS Applied Materials \& Interfaces},

volume = {11},

number = {5},

pages = {5129-5135},

abstract = {The oxygen reduction reaction (ORR) is of great interest for future sustainable energy conversion and storage, especially concerning fuel cell applications. The preparation of active, affordable, and scalable electrocatalysts and their application in fuel cell engines of hydrogen cars is a prominent step toward the reduction of air pollution, especially in urban areas. Alloying nanostructured Pt with lanthanides is a promising approach to enhance its catalytic ORR activity, whereby the development of a simple synthetic route turned out to be a nontrivial endeavor. Herein, for the first time, we present a successful single-step, scalable top-down synthetic route for Pt\textendashlanthanide alloy nanoparticles, as witnessed by the example of Pr-alloyed Pt nanoparticles. The catalyst was characterized by high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and photoelectron spectroscopy, and its electrocatalytic oxygen reduction activity was investigated using a rotating disk electrode technique. PtxPr/C showed ∼3.5 times higher [1.96 mA/cm2Pt, 0.9 V vs reversible hydrogen electrode (RHE)] specific activity and ∼1.7 times higher (0.7 A/mgPt, 0.9 V vs RHE) mass activity compared to commercial Pt/C catalysts. On the basis of previous findings and characterization of the PtxPr/C catalyst, the activity improvement over commercial Pt/C originates from a lattice strain introduced by the alloying process.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}