@misc{FischerFoersterAballeetal., author = {Fischer, Simon and Foerster, Michael and Aballe, Lucia and Vonk, Vedran and Falta, Jens and Krisponeit, Jon-Olaf and Flege, Jan Ingo}, title = {Vanadium dioxide thin films on (100)- and (110)-oriented ruthenium dioxide islands}, series = {Verhandlungen der DPG}, journal = {Verhandlungen der DPG}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {330 -- 330}, abstract = {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.}, language = {en} } @misc{KaoScheweAkhtaretal., author = {Kao, Ming-Chao and Schewe, Lukas Paul and Akhtar, Arub and Rehm, Jana and Bin Anooz, Saud Bin and Galazka, Zbigniew and Popp, Andreas and Flege, Jan Ingo and Vonk, Vedran and Stierle, Andreas}, title = {Structure and Stability of Al-alloyed β-Ga2O3(100) surfaces}, series = {Verhandlungen der DPG, Berlin 2024}, journal = {Verhandlungen der DPG, Berlin 2024}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {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.}, language = {en} }