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 Applied Physics Letters, 116 (5), pp. 052101, 2020. Links | Tags: Foundry Inorganic, Molecularly-Functionalized @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 = {2020-01-01}, journal = {Applied Physics Letters}, volume = {116}, number = {5}, pages = {052101}, keywords = {Foundry Inorganic, Molecularly-Functionalized}, pubstate = {published}, tppubtype = {article} } |
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 Advanced Materials, 32 (4), pp. 1905458, 2020, ISSN: 0935-9648. Abstract | Links | Tags: Foundry Inorganic, Molecularly-Functionalized @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 = {2020}, date = {2020-01-01}, 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 = {Foundry Inorganic, Molecularly-Functionalized}, 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. |
Y Negrín-Montecelo, M Comesaña-Hermo, L K Khorashad, A Sousa-Castillo, Z Wang, M Pérez-Lorenzo, T Liedl, A O Govorov, M A Correa-Duarte ACS Energy Letters, pp. 395-402, 2019. Links | Tags: Foundry Inorganic, Molecularly-Functionalized @article{, title = {Photophysical Effects behind the Efficiency of Hot Electron Injection in Plasmon-Assisted Catalysis: The Joint Role of Morphology and Composition}, author = {Y Negr\'{i}n-Montecelo and M Comesa\~{n}a-Hermo and L K Khorashad and A Sousa-Castillo and Z Wang and M P\'{e}rez-Lorenzo and T Liedl and A O Govorov and M A Correa-Duarte}, url = {https://doi.org/10.1021/acsenergylett.9b02478}, doi = {10.1021/acsenergylett.9b02478}, year = {2019}, date = {2019-12-12}, journal = {ACS Energy Letters}, pages = {395-402}, keywords = {Foundry Inorganic, Molecularly-Functionalized}, pubstate = {published}, tppubtype = {article} } |
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 Nanotechnology, 30 (49), pp. 495703, 2019, ISSN: 0957-4484 1361-6528. Abstract | Links | Tags: Foundry Inorganic, Molecularly-Functionalized @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 = {Foundry Inorganic, Molecularly-Functionalized}, 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. |
M. Mallmann, R. Niklaus, T. Rackl, M. Benz, T. G. Chau, D. Johrendt, J. Minár, W. Schnick Chem. Eur. J., 25 , pp. 1-10, 2019, ISSN: 1521-3765. Abstract | Links | Tags: Foundry Inorganic @article{Mallmann2019, title = {Solid Solutions of Grimm\textendashSommerfeld Analogous Nitride Semiconductors II‐IV‐N2 (II=Mg, Mn, Zn; IV=Si, Ge): Ammonothermal Synthesis and DFT Calculations }, author = {M. Mallmann and R. Niklaus and T. Rackl and M. Benz and T. G. Chau and D. Johrendt and J. Min\'{a}r and W. Schnick}, doi = {https://doi.org/10.1002/chem.201903897}, issn = {1521-3765}, year = {2019}, date = {2019-09-17}, journal = {Chem. Eur. J.}, volume = {25}, pages = {1-10}, abstract = {Grimm\textendashSommerfeld analogous II‐IV‐N2 nitrides such as ZnSiN2, ZnGeN2, and MgGeN2 are promising semiconductor materials for substitution of commonly used (Al,Ga,In)N. Herein, the ammonothermal synthesis of solid solutions of II‐IV‐N2 compounds (II=Mg, Mn, Zn; IV=Si, Ge) having the general formula (IIa1−xIIbx)‐IV‐N2 with x≈0.5 and ab initio DFT calculations of their electronic and optical properties are presented. The ammonothermal reactions were conducted in custom‐built, high‐temperature, high‐pressure autoclaves by using the corresponding elements as starting materials. NaNH2 and KNH2 act as ammonobasic mineralizers that increase the solubility of the reactants in supercritical ammonia. Temperatures between 870 and 1070 K and pressures up to 200 MPa were chosen as reaction conditions. All solid solutions crystallize in wurtzite‐type superstructures with space group Pna21 (no. 33), confirmed by powder XRD. The chemical compositions were analyzed by energy‐dispersive X‐ray spectroscopy. Diffuse reflectance spectroscopy was used for estimation of optical bandgaps of all compounds, which ranged from 2.6 to 3.5 eV (Ge compounds) and from 3.6 to 4.4 eV (Si compounds), and thus demonstrated bandgap tunability between the respective boundary phases. Experimental findings were corroborated by DFT calculations of the electronic structure of pseudorelaxed mixed‐occupancy structures by using the KKR+CPA approach.}, keywords = {Foundry Inorganic}, pubstate = {published}, tppubtype = {article} } Grimm–Sommerfeld analogous II‐IV‐N2 nitrides such as ZnSiN2, ZnGeN2, and MgGeN2 are promising semiconductor materials for substitution of commonly used (Al,Ga,In)N. Herein, the ammonothermal synthesis of solid solutions of II‐IV‐N2 compounds (II=Mg, Mn, Zn; IV=Si, Ge) having the general formula (IIa1−xIIbx)‐IV‐N2 with x≈0.5 and ab initio DFT calculations of their electronic and optical properties are presented. The ammonothermal reactions were conducted in custom‐built, high‐temperature, high‐pressure autoclaves by using the corresponding elements as starting materials. NaNH2 and KNH2 act as ammonobasic mineralizers that increase the solubility of the reactants in supercritical ammonia. Temperatures between 870 and 1070 K and pressures up to 200 MPa were chosen as reaction conditions. All solid solutions crystallize in wurtzite‐type superstructures with space group Pna21 (no. 33), confirmed by powder XRD. The chemical compositions were analyzed by energy‐dispersive X‐ray spectroscopy. Diffuse reflectance spectroscopy was used for estimation of optical bandgaps of all compounds, which ranged from 2.6 to 3.5 eV (Ge compounds) and from 3.6 to 4.4 eV (Si compounds), and thus demonstrated bandgap tunability between the respective boundary phases. Experimental findings were corroborated by DFT calculations of the electronic structure of pseudorelaxed mixed‐occupancy structures by using the KKR+CPA approach. |
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 Nature Communications, 10 (1), pp. 2755, 2019, ISSN: 2041-1723. Abstract | Links | Tags: Foundry Inorganic @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 = {Foundry Inorganic}, 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. |
A Vogel, T Miller, C Hoch, M Jakob, O Oeckler, T Nilges Cu9.1Te4Cl3: A Thermoelectric Compound with Low Thermal and High Electrical Conductivity Journal Article Inorganic Chemistry, 58 (9), pp. 6222-6230, 2019, ISSN: 0020-1669. Abstract | Links | Tags: Foundry Inorganic @article{, title = {Cu9.1Te4Cl3: A Thermoelectric Compound with Low Thermal and High Electrical Conductivity}, author = {A Vogel and T Miller and C Hoch and M Jakob and O Oeckler and T Nilges}, url = {https://doi.org/10.1021/acs.inorgchem.9b00453}, doi = {10.1021/acs.inorgchem.9b00453}, issn = {0020-1669}, year = {2019}, date = {2019-05-06}, journal = {Inorganic Chemistry}, volume = {58}, number = {9}, pages = {6222-6230}, abstract = {Cu9.1Te4Cl3 is a new polymorphic compound in the class of coinage metal polytelluride halides. Copper is highly mobile, which results in multiple order\textendashdisorder phase transitions in a limited temperature interval from 240 to 370 K. Mainly as a consequence of thermal transport properties, the compound’s thermoelectric figure of merit reaches values up to ZT = 0.15 in the temperature range between room temperature and 523 K. Its structure is closely related to that of Ag10Te4Br3, another coinage metal polytelluride halide, which represents the first p\textendashn\textendashp-switchable semiconductor approachable by a simple temperature change. The title compound outperforms Ag10Te4Br3 in terms of thermoelectric properties by 1 order of magnitude and therefore acts as a link between the class of p\textendashn\textendashp compounds and thermoelectric materials.}, keywords = {Foundry Inorganic}, pubstate = {published}, tppubtype = {article} } Cu9.1Te4Cl3 is a new polymorphic compound in the class of coinage metal polytelluride halides. Copper is highly mobile, which results in multiple order–disorder phase transitions in a limited temperature interval from 240 to 370 K. Mainly as a consequence of thermal transport properties, the compound’s thermoelectric figure of merit reaches values up to ZT = 0.15 in the temperature range between room temperature and 523 K. Its structure is closely related to that of Ag10Te4Br3, another coinage metal polytelluride halide, which represents the first p–n–p-switchable semiconductor approachable by a simple temperature change. The title compound outperforms Ag10Te4Br3 in terms of thermoelectric properties by 1 order of magnitude and therefore acts as a link between the class of p–n–p compounds and thermoelectric materials. |
C Ott, F Reiter, M Baumgartner, M Pielmeier, A Vogel, P Walke, S Burger, M Ehrenreich, G Kieslich, D Daisenberger, J Armstrong, U K Thakur, P Kumar, S Chen, D Donadio, L S Walter, R T Weitz, K Shankar, T Nilges Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems Based on SnIP Journal Article Advanced Functional Materials, 29 (18), pp. 1900233, 2019, ISSN: 1616-301X. Abstract | Links | Tags: Foundry Inorganic @article{, title = {Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems Based on SnIP}, author = {C Ott and F Reiter and M Baumgartner and M Pielmeier and A Vogel and P Walke and S Burger and M Ehrenreich and G Kieslich and D Daisenberger and J Armstrong and U K Thakur and P Kumar and S Chen and D Donadio and L S Walter and R T Weitz and K Shankar and T Nilges}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.201900233}, doi = {10.1002/adfm.201900233}, issn = {1616-301X}, year = {2019}, date = {2019-03-13}, journal = {Advanced Functional Materials}, volume = {29}, number = {18}, pages = {1900233}, abstract = {Abstract Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core\textendashshell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.}, keywords = {Foundry Inorganic}, pubstate = {published}, tppubtype = {article} } Abstract Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting. |
PublicationsPeter Sonntag2020-02-06T17:19:45+01:00
Demonstration of n-type behavior in catalyst-free Si-doped GaAs nanowires grown by molecular beam epitaxy Journal Article Applied Physics Letters, 116 (5), pp. 052101, 2020. |
Quantum-Confinement-Enhanced Thermoelectric Properties in Modulation-Doped GaAs–AlGaAs Core–Shell Nanowires Journal Article Advanced Materials, 32 (4), pp. 1905458, 2020, ISSN: 0935-9648. |
ACS Energy Letters, pp. 395-402, 2019. |
Optical absorption of composition-tunable InGaAs nanowire arrays Journal Article Nanotechnology, 30 (49), pp. 495703, 2019, ISSN: 0957-4484 1361-6528. |
Chem. Eur. J., 25 , pp. 1-10, 2019, ISSN: 1521-3765. |
Site-selectively generated photon emitters in monolayer MoS2 via local helium ion irradiation Journal Article Nature Communications, 10 (1), pp. 2755, 2019, ISSN: 2041-1723. |
Cu9.1Te4Cl3: A Thermoelectric Compound with Low Thermal and High Electrical Conductivity Journal Article Inorganic Chemistry, 58 (9), pp. 6222-6230, 2019, ISSN: 0020-1669. |
Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems Based on SnIP Journal Article Advanced Functional Materials, 29 (18), pp. 1900233, 2019, ISSN: 1616-301X. |