TY - GEN A1 - Ewert, Moritz A1 - Schmidt, Thomas A1 - Flege, Jan Ingo A1 - Heidmann, Inga A1 - Grzela, Tomasz A1 - Klesse, Wolfgang Matthias A1 - Förster, M. A1 - Aballe, Lucia A1 - Schröder, Thomas T1 - Morphology and Chemical Composition of Co Germanide islands on Ge(001): in-situ nanoscale insights into contact formation for Ge-based device technology T2 - Nanotechnology Y1 - 2016 SN - 1361-6528 SN - 0957-4484 VL - 27 IS - 32 SP - 325705 ER - TY - GEN A1 - Grzela, Tomasz A1 - Capellini, Giovanni A1 - Koczorowski, Wojciech A1 - Schubert, Markus Andreas A1 - Czajka, Ryszard A1 - Curson, Neil J. A1 - Heidmann, Inga A1 - Schmidt, Thomas A1 - Falta, Jens A1 - Schröder, Thomas T1 - Growth and evolution of nickel – germanide nanonstructures on Ge(001) T2 - Nanotechnology Y1 - 2015 SN - 1361-6528 SN - 0957-4484 VL - 26 IS - 38 SP - 385701 ER - TY - JOUR A1 - Heine, A. A1 - Ripke, E. A1 - Schmidt, Thomas T1 - Leistungsverbesserung der Kläranlage einer Papierfabrik Y1 - 2001 ER - TY - GEN A1 - Schmidt, Thomas A1 - Ahrens, Christian A1 - Flege, Jan Ingo A1 - Jaye, Cherno A1 - Fischer, Daniel A. A1 - Falta, Jens T1 - Growth of Epitaxial 3,4,9,10-Perylene Tetracarboxylic Dianhydride on Bi-Terminated Silicon T2 - Journal of Physical Chemistry C N2 - The epitaxial quality of thin films crucially depends on their interaction with the substrate. Up to now, Ag-terminated Si(111) has been employed as the model substrate for the growth of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on semiconductors. In this study, we will show that Bi termination results in PTCDA films of superior epitaxial quality. We have studied the growth of PTCDA on bismuth-passivated Si(111) in detail by means of spot profile analysis of low-energy electron diffraction (SPA-LEED), X-ray photoemission spectroscopy (XPS), near-edge X-ray absorptionfine structure (NEXAFS), and scanning tunneling microscopy (STM). The XPS results reveal the presence of intact PTCDA molecules on the surface upon adsorption. NEXAFS data indicate the PTCDA molecules being oriented with their molecular plane parallel to the surface. STM shows a very smooth growth front of the PTCDA film, preserving the step structure of the substrate. High-resolution SPA-LEED data demonstrate the presence of a multidomain surface with a rich variety of PTCDA surface structures, which were identified to be most prominently herring-bone polytypes. However, in the monolayer range, quadratic brick-wall structures and a nearly square-like structure as well as a perylene-like structure have also been found. Despite the simultaneous presence of multiple domains, the individual domains show excellent lateral ordering, with larger domain sizes as compared to the case of Ag-terminated Si(111). KW - dianhydride KW - Bi-terminated silicon KW - spot profile analysis of low-energy electron diffraction (SPA-LEED) KW - X-ray photoemission spectroscopy (XPS) KW - near-edge X-ray absorptionfine structure (NEXAFS) KW - scanning tunneling microscopy (STM) Y1 - 2019 U6 - https://doi.org/10.1021/acs.jpcc.8b10396 SN - 1932-7447 SN - 1932-7455 VL - 123 IS - 12 SP - 7097 EP - 7109 ER - TY - GEN A1 - Schmidt, Thomas A1 - Buß, Lars A1 - Ewert, Moritz A1 - Schönhoff, Gunnar A1 - Wehling, Tim Oliver A1 - Falta, Jens T1 - Adsorption of sulfur on Si(111) T2 - Surface Science N2 - The adsorption of S on Si(111)- 7 × 7 has been investigated for different preparation schemes and parameters. S was supplied from an electrochemical Ag2S cell. For room temperature adsorption and subsequent annealing, no ordered S induced reconstruction can be observed with spot profile analysis low-energy electron diffraction (SPALEED). S deposition at temperatures above about 400°C, however, leads to a well-ordered reconstruction. Judging from the LEED pattern, the same reconstruction was already observed by Metzner et al. [Surf. Sci. 377–379(1997) 71–74] who identified it as 4 × 4 reconstruction. The upper temperature limit for the pre-paration of this superstructure depends on S flux, which is needed to compensate for desorption. Prolonged S exposure leads to surface roughening, as observed with SPALEED and scanning tunneling microscopy (STM), pointing to surface etching by S. From our SPALEED data, we can conclude that the observed reconstruction is not a 4 × 4 reconstruction, but a 20/12 superstructure with a rectangular unit cell that exists in three rotational domains, as confirmed by STM. Different structural trial models have been assessed with density functional theory. Among these model structures, a configuration with dimers adsorbed on bridging sites, with a S coverage of 1 monolayer, is most likely, since it is energetically favorable and is in agreement with all experimental results. KW - Passivation KW - Low-energy electron diffraction KW - Scanning tunneling microscopy KW - Density functional theory KW - Auger electron spectroscopy Y1 - 2020 U6 - https://doi.org/10.1016/j.susc.2019.121561 SN - 0039-6028 SN - 1879-2758 VL - 694 ER - TY - GEN A1 - Krisponeit, Jon-Olaf A1 - Fischer, Simon A1 - Esser, Sven A1 - Moshnyaga, Vasily A1 - Schmidt, Thomas A1 - Piper, Louis F. J. A1 - Flege, Jan Ingo A1 - Falta, Jens T1 - The morphology of VO2/TiO2(001): terraces, facets, and cracks T2 - Scientific Reports N2 - Vanadium dioxide (VO2) features a pronounced, thermally-driven metal-to-insulator transition at 340 K. Employing epitaxial stress on rutile TiO2(001) substrates, the transition can be tuned to occur close to room temperature. Striving for applications in oxide-electronic devices, the lateral homogeneity of such samples must be considered as an important prerequisite for efforts towards miniaturization. Moreover, the preparation of smooth surfaces is crucial for vertically stacked devices and, hence, the design of functional interfaces. Here, the surface morphology of VO2/TiO2(001) films was analyzed by low-energy electron microscopy and diffraction as well as scanning probe microscopy. The formation of large terraces could be achieved under temperature-induced annealing, but also the occurrence of facets was observed and characterized. Further, we report on quasi-periodic arrangements of crack defects which evolve due to thermal stress under cooling. While these might impair some applicational endeavours, they may also present crystallographically well-oriented nano-templates of bulk-like properties for advanced approaches. KW - Vanadium dioxide (VO2) KW - rutile TiO2(001) KW - metal-to-insulator transition KW - morphology KW - crystallography KW - low-energy electron microscopy (LEEM) KW - low-energy electron diffraction (LEED) KW - scanning probe microscopy Y1 - 2020 U6 - https://doi.org/10.1038/s41598-020-78584-9 SN - 2045-2322 VL - 10 ER - TY - GEN A1 - Pozarowska, Emilia A1 - Pleines, Linus A1 - Prieto, Mauricio J. A1 - Tănase, Liviu Christian A1 - Souza Caldas, Lucas de A1 - Tiwari, Aarti A1 - Schmidt, Thomas A1 - Falta, Jens A1 - Morales, Carlos A1 - Flege, Jan Ingo T1 - The relation between structure sensitivity and doping of ceria(111) vs. ceria(100) T2 - Verhandlungen der DPG N2 - CeOx-Cu inverse catalysts have been shown to convert CO2 into valuable chemicals through catalytic hydrogenation. The catalytic activity may further be enhanced by alloying ceria with trivalent, catalytically active metals, such as Sm, promoting the formation of Ce3+ active sites. In this work, the structural and chemical properties of (111)- and (100)- oriented CeOx islands alloyed with samarium were explored by low-energy electron microscopy and X-ray photoemission electron microscopy. After Sm deposition on the as-grown CeOx islands, the near-surface region of (100)-oriented CeOx is reduced after exposure to H2 at 470 ∘C, whereas the deeper layers as well as the whole (111)-oriented islands retain the Ce4+ state. Subsequent reoxidation with O2 leads to the complete Ce4+ state recovery, suggesting the healing of oxygen vacancies. Additional annealing at 470 ∘C induces samarium diffusion into the ceria matrix. Yet, subsequent exposure to H2 reduces neither the (111)- nor the (100)-oriented CeSmOx islands, suggesting a quite unexpected stability of this system. KW - catalytic hydrogenation KW - Samarium alloying of cerium oxide KW - low-energy electron microscopy (LEEM) KW - X-ray photoemission electron microscopy (PEEM) KW - healing of oxygen vacancies Y1 - 2022 UR - https://www.dpg-verhandlungen.de/year/2022/conference/regensburg/part/o/session/52/contribution/11 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Pożarowska, Emilia A1 - Pleines, Linus A1 - Ewert, Moritz A1 - Prieto, Mauricio J. A1 - Tănase, Liviu Christian A1 - Souza Caldas, Lucas de A1 - Tiwari, Aarti A1 - Schmidt, Thomas A1 - Falta, Jens A1 - Krasovskii, Eugene A1 - Morales, Carlos A1 - Flege, Jan Ingo T1 - Preparation and stability of the hexagonal phase of samarium oxide on Ru(0001) T2 - Ultramicroscopy N2 - We have used low-energy electron microscopy (LEEM), micro-illumination low-energy electron diffraction (µLEED) supported by ab initio calculations, and X-ray absorption spectroscopy (XAS) to investigate in-situ and in real-time the structural properties of Sm2O3 deposits grown on Ru(0001), a rare-earth metal oxide model catalyst. Our results show that samarium oxide grows in a hexagonal A-Sm2O3 phase on Ru(0001), exhibiting a (0001) oriented-top facet and (113) side facets. Upon annealing, a structural transition from the hexagonal to cubic phase occurs, in which the Sm cations exhibit the +3 oxidation state. The unexpected initial growth in the A-Sm2O3 hexagonal phase and its gradual transition to a mixture with cubic C-Sm2O3 showcases the complexity of the system and the critical role of the substrate in the stabilization of the hexagonal phase, which was previously reported only at high pressures and temperatures for bulk samaria. Besides, these results highlight the potential interactions that Sm could have with other catalytic compounds with respect to the here gathered insights on the preparation conditions and the specific compounds with which it interacts. KW - Samarium oxide (Sm2O3) KW - low-energy electron microscopy (LEEM) KW - X-ray photoemission electron microscopy (XPEEM) KW - Facets KW - Epitaxy KW - Hexagonal phase Y1 - 2023 U6 - https://doi.org/10.1016/j.ultramic.2023.113755 SN - 0304-3991 SN - 1879-2723 VL - 250 ER - TY - GEN A1 - Tschammer, Rudi A1 - Buß, Lars A1 - Pożarowska, Emilia A1 - Morales, Carlos A1 - Senanayake, Sanjaya D. A1 - Prieto, Mauricio J. A1 - Tănase, Liviu C. A1 - de Souza Caldas, Lucas A1 - Tiwari, Aarti A1 - Schmidt, Thomas A1 - Niño, Miguel A. A1 - Foerster, Michael A1 - Falta, Jens A1 - Flege, Jan Ingo T1 - High-temperature growth of CeOx on Au(111) and behavior under reducing and oxidizing conditions T2 - The journal of physical chemistry C N2 - Inverse oxide–metal model catalysts can show superior activity and selectivity compared with the traditional supported metal–oxide architecture, commonly attributed to the synergistic overlayer–support interaction. We have investigated the growth and redox properties of ceria nanoislands grown on Au(111) between 700 and 890 °C, which yields the CeO2–Au(111) model catalyst system. We have observed a distinct correlation between deposition temperature, structural order, and oxide composition through low-energy electron microscopy, low-energy electron diffraction, intensity–voltage curves, and X-ray absorption spectroscopy. Improved structural order and thermal stability of the oxide have been achieved by increasing the oxygen chemical potential at the substrate surface using reactive oxygen (O/O2) instead of molecular O2 during growth. In situ characterization under reducing (H2) and oxidizing atmospheres (O2, CO2) indicates an irreversible loss of structural order and redox activity at high reduction temperatures, while moderate temperatures result in partial decomposition of the ceria nanoislands (Ce3+/Ce4+) to metallic cerium (Ce0). The weak interaction between Au(111) and CeOx would facilitate its reduction to the Ce0 metallic state, especially considering the comparatively strong interaction between Ce0 and Au0. Besides, the higher reactivity of atomic oxygen promotes a stronger interaction between the gold and oxide islands during the nucleation process, explaining the improved stability. Thus, we propose that by driving the nucleation and growth of the ceria/Au system in a highly oxidizing regime, novel chemical properties can be obtained. KW - Inverse oxide-metal model catalysts KW - Ceria nanoislands KW - Growth KW - Redox properties KW - Low-energy electron microscopy (LEEM) KW - Low-energy electron diffraction (LEED) KW - Intensity–voltage curves KW - X-ray absorption spectroscopy (XAS) Y1 - 2025 U6 - https://doi.org/10.1021/acs.jpcc.4c08072 SN - 1932-7447 VL - 129 IS - 7 SP - 3583 EP - 3594 PB - American Chemical Society (ACS) CY - Washington, DC ER - TY - GEN A1 - Braud, Nicolas A1 - Buß, Lars A1 - Merte, Lindsay Richard A1 - Wallander, Harald A1 - Krisponeit, Jon-Olaf A1 - Schmidt, Thomas A1 - Lundgren, Edvin A1 - Flege, Jan Ingo A1 - Falta, Jens T1 - Growth and oxidation of ultra-thin Pt-Sn layers on Pt(111) by molecular and atomic oxygen T2 - Ultramicroscopy N2 - The preparation of ultra-thin PtSn-alloyed layers by molecular beam epitaxy was studied using low-energy electron microscopy (LEEM) and micro-diffraction (-LEED). Deposition at a sample temperature of 435 °C initially results in the formation of a PtSn/Pt(111) layer showing a (2 × 2) reconstruction. With continued Sn deposition, a PtSn/Pt(111) layer develops, showing a ()R30° reconstruction. An ultra-thin tin oxide was formed from the (2 × 2) surface by exposure to molecular oxygen at temperatures of 500 °C and 590 °C, respectively. LEED shows the evolution of a new surface structure, which could be identified as an incommensurate rectangular reconstruction with lattice parameters of a = (6.4 ± 0.1) Å and b = (8.6 ± 0.1) Å present in three domains rotated by 120° with respect to each other. This structure can be related to the zigzag reconstructions found for similar ultra-thin oxide systems. Contrarily, the ()R30° structure showed no oxide formation even after extensive exposure to molecular oxygen. The usage of atomic oxygen, however, allows for oxidation of this surface and the growth of thicker oxides on both types of overlayers. At 500 °C this process is accompanied by substantial roughening of the surface. KW - Tin KW - Platinum KW - Tin oxide KW - Platinum-tin KW - Oxidation KW - SnOx KW - Ultra-thin films KW - LEED KW - LEEM Y1 - 2025 U6 - https://doi.org/10.1016/j.ultramic.2025.114243 SN - 0304-3991 VL - 278 SP - 1 EP - 11 PB - Elsevier BV CY - Amsterdam ER - TY - GEN A1 - Pożarowska, Emilia A1 - Pleines, Linus A1 - Prieto, Mauricio J. A1 - Tănase, Liviu C. A1 - de Souza Caldas, Lucas A1 - Tiwari, Aarti A1 - Schmidt, Thomas A1 - Falta, Jens A1 - Morales, Carlos A1 - Flege, Jan Ingo T1 - The relationship between Sm alloying and structure sensitivity of ceria(111)- and (100)-oriented nanoislands on Cu(111) T2 - Physical chemistry, chemical physics N2 - We have investigated the complex dynamics of samarium deposition on ceria islands of different orientations, namely (111) and (100), grown side by side on a Cu(111) single-crystal substrate, followed by post-oxidation and annealing under ultra-high vacuum conditions. Only the (100)-oriented ceria islands undergo substantial initial reduction upon samarium deposition at 740 K via a pathway similar to the strong Ce–ceria interfacial interaction, while the (111)-oriented islands remain in the Ce4+ oxidation state. This remarkable structure sensitivity is explained by the different energies required for oxygen vacancy formation for both oxide orientations. Subsequent mild re-oxidation with O2 results in the complete recovery of the Ce4+ oxidation state in the (100)-oriented islands, indicating the complete healing of oxygen vacancies. In contrast, extended annealing at moderate temperatures likely induces persistent samarium incorporation into the cerium oxide matrix. Our results provide new insights into the complex structure–activity relationships in mixed rare-earth metal oxide systems and have promising implications for optimizing catalytic reactions over such compounds in reducing environments. KW - LEEM Y1 - 2025 U6 - https://doi.org/10.1039/D5CP01171J SN - 1463-9076 VL - 27 IS - 29 SP - 15691 EP - 15703 PB - Royal Society of Chemistry (RSC) CY - Cambridge ER -