TY - GEN A1 - Fischer, Simon A1 - Foerster, Michael A1 - Aballe, Lucia A1 - Vonk, Vedran A1 - Falta, Jens A1 - Krisponeit, Jon-Olaf A1 - Flege, Jan Ingo T1 - Vanadium dioxide thin films on (100)- and (110)-oriented ruthenium dioxide islands T2 - Verhandlungen der DPG N2 - Bulk vanadium dioxide exhibits a metal-insulator transition at 68 ∘C. Because this change in resistivity is linked to a structural transition, the transition temperature can be tuned by epitaxial strain. Due to the high lattice mismatch of RuO2 with VO2, this substrate promises a highly shifted transition temperature, which enables new types of switching devices, smart coatings, and sensors. It is prepared by oxidizing a Ru(0001) crystal, providing micron-sized, (110)- as well as (100)-oriented RuO2 islands simultaneously. One of the challenges in preparing VO2 is to reliably meet the desired stoichiometry. We investigated the vanadium oxidation state using local XAS and XPS measurements taken at a synchrotron-based XPEEM instrument, revealing that VO2 stoichiometry is maintained throughout the entire film. This was found not only on RuO2(100) and RuO2(110), but also on the bare ruthenium substrate. The VO2 film thickness was determined to 3.6 nm by ex situ XRR measurements. Financial support from the DFG is acknowledged. KW - transition temperature KW - strain KW - synchrotron-based XPEEM KW - local X-Ray absorption spectroscopy (XAS) KW - local X-Ray photoelectron spectroscopy (XPS) Y1 - 2019 UR - https://www.dpg-verhandlungen.de/year/2019/conference/regensburg/part/o/session/37/contribution/5 SN - 0420-0195 SP - 330 EP - 330 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Kao, Ming-Chao A1 - Schewe, Lukas Paul A1 - Akhtar, Arub A1 - Rehm, Jana A1 - Bin Anooz, Saud Bin A1 - Galazka, Zbigniew A1 - Popp, Andreas A1 - Flege, Jan Ingo A1 - Vonk, Vedran A1 - Stierle, Andreas T1 - Structure and Stability of Al-alloyed β-Ga2O3(100) surfaces T2 - Verhandlungen der DPG, Berlin 2024 N2 - β-Ga2O3 (GaO) holds great promise in high-power applications. GaO is predicted to outperform the leading technologies based on SiC and GaN due to a three times higher calculated critical field strength. It has been identified that alloying with Al results in an almost linear increase in the bandgap between Ga2O3 (4.85eV) and Al2O3 (7eV). A critical issue in the bandgap engineering of GaO is maintaining reasonable electron mobility, which is low for the pure material (150cm2/V/S). This project aims to explore GaO by Al alloying, which allows tunable wide bandgaps for engineering material properties and at the same time maintains excellent crystal quality. PXRD and their Rietveld refinement on several AlGaO crystals indicate a preferential ordering of Al and Ga over octahedral and tetrahedral sites. The results of an SXRD study using synchrotron radiation addressing the surface structure of β-AlxGa2−xO3(100) substrates with x=0−0.25. Our results indicate that the GaO(100) surface is nearly bulk terminated and remains smooth up to 800°C and 10−5mbar of molecular oxygen. KW - high-power applications KW - bandgap engineering KW - crystal quality KW - X-ray diffraction Y1 - 2024 UR - https://www.dpg-verhandlungen.de/year/2024/conference/berlin/part/o/session/67/contribution/10 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Kao, Ming-Chao A1 - Schewe, Lukas Paul A1 - Akhtar, Arub A1 - Vlad, Alina A1 - Keller, Thomas F. A1 - Henkel, Karsten A1 - Anooz, Saud Bin A1 - Popp, Andreas A1 - Galazka, Zbigniew A1 - Flege, Jan Ingo A1 - Stierle, Andreas A1 - Vonk, Vedran T1 - Surface termination of β-Ga₂O₃(100) as-cleaved single crystals T2 - Applied physics letters N2 - The surface of β-Ga₂O₃ single crystals cleaved along their (100) plane is investigated using surface x-ray diffraction and atomic force microscopy. The results show the surface to consist of a single, so-called B-termination, which means that the crystal cleaves at planes formed by edge-sharing oxygen octahedra, thereby breaking the longest and weakest Ga–O bonds. Refinement of the atomic positions results in small displacements from the bulk structure, at most approximately 0.01 Å. Atomic force microscopy suggests that relatively large terraces form together with steps of half the a-axis length of approximately 0.6 nm, which means that terraces have the same atomic termination, related by the crystal symmetry. These results are important as a fundamental property of β-Ga₂O₃ when processed or used in various semiconductor applications. KW - X-ray KW - Gallium oxide Y1 - 2026 U6 - https://doi.org/10.1063/5.0309937 SN - 0003-6951 VL - 128 IS - 7 SP - 1 EP - 5 PB - AIP Publishing CY - Melville, NY ER -