TY - GEN A1 - Ferbel, Letizia A1 - Veronesi, Stefano A1 - Mentes, Tevfik Onur A1 - Buß, Lars A1 - Rossi, Antonio A1 - Mishra, Neeraj A1 - Coletti, Camilla A1 - Flege, Jan Ingo A1 - Locatelli, Andrea A1 - Heun, Stefan T1 - Rubidium intercalation in epitaxial monolayer graphene T2 - Nanoscale N2 - Alkali metal intercalation of graphene layers has been of particular interest due to potential applications in electronics, energy storage, and catalysis. Rubidium (Rb) is one of the largest alkali metals and among the least investigated as an intercalant. Here, we report a systematic investigation, with a multi-technique approach, of the phase formation of Rb under epitaxial monolayer graphene on SiC(0001). We explore a wide phase space with two control parameters: the Rb density (i.e., deposition time) and sample temperature (i.e., room and low temperature). We reveal the emergence of (2 × 2) and [sqrt(3) x (sqrt3)] R30° structures formed by a single alkali metal layer intercalated between monolayer graphene and the interfacial C-rich reconstructed surface, also known as the buffer layer. Rb intercalation also results in strong n-type doping of the graphene layer. Upon progressively annealing to higher temperatures, we first reveal the diffusion of Rb atoms, which results in the enlargement of intercalated areas. As desorption sets in, intercalated regions progressively shrink and fragment. Eventually, at approximately 600 °C, the initial surface is retrieved, indicating the reversibility of the intercalation process. KW - Graphene KW - N-type doping KW - Micro-spot low-energy electron diffraction (µLEED) KW - Scanning tunneling microscopy (STM) KW - Low-energy electron microscopy (LEEM) KW - Density functional theory (DFT) Y1 - 2025 U6 - https://doi.org/10.1039/D5NR00417A SN - 2040-3364 VL - 17 IS - 19 SP - 12465 EP - 12472 PB - Royal Society of Chemistry (RSC) CY - London 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 - Richter, Jana A1 - Rachow, Fabian A1 - Israel, Johannes A1 - Roth, Norbert A1 - Charlafti, Evgenia A1 - Günther, Vivien A1 - Flege, Jan Ingo A1 - Mauß, Fabian T1 - Reaction Mechanism Development for Methane Steam Reforming on a Ni/Al2O3 Catalyst T2 - Catalysts N2 - In this work, a reliable kinetic reaction mechanism was revised to accurately reproduce the detailed reaction paths of steam reforming of methane over a Ni/Al2O3 catalyst. A steady-state fixed-bed reactor experiment and a 1D reactor catalyst model were utilized for this task. The distinctive feature of this experiment is the possibility to measure the axially resolved temperature profile of the catalyst bed, which makes the reaction kinetics inside the reactor visible. This allows for understanding the actual influence of the reaction kinetics on the system; while pure gas concentration measurements at the catalytic reactor outlet show near-equilibrium conditions, the inhere presented temperature profile shows that it is insufficient to base a reaction mechanism development on close equilibrium data. The new experimental data allow for achieving much higher quality in the modeling efforts. Additionally, by carefully controlling the available active surface via dilution in the experiment, it was possible to slow down the catalyst conversion rate, which helped during the adjustment of the reaction kinetics. To assess the accuracy of the revised mechanism, a monolith experiment from the literature was simulated. The results show that the fitted reaction mechanism was able to accurately predict the experimental outcomes for various inlet mass flows, temperatures, and steam-to-carbon ratios. KW - kinetic reaction mechanism development KW - 1D modeling KW - reaction rates KW - methane steam reforming KW - fixed-bed reactor experiments KW - nickel catalyst Y1 - 2023 U6 - https://doi.org/10.3390/catal13050884 SN - 2073-4344 VL - 13 IS - 5 ER - TY - GEN A1 - Kedia, Mayank A1 - Das, Chittaranjan A1 - Kot, Malgorzata A1 - Yalcinkaya, Yenal A1 - Zuo, Weiwei A1 - Tabah Tanko, Kenedy A1 - Matvija, Peter A1 - Ezquer, Mikel A1 - Cornago, Iñaki A1 - Hempel, Wolfram A1 - Kauffmann, Florian A1 - Plate, Paul A1 - Lira-Cantu, Monica A1 - Weber, Stefan A.L. A1 - Saliba, Michael T1 - Mitigating the amorphization of perovskite layers by using atomic layer deposition of alumina T2 - Energy & environmental science N2 - Atomic layer deposition of aluminum oxide (ALD-Al2O3) layers has recently been studied for stabilizing perovskite solar cells (PSCs) against environmental stressors, such as humidity and oxygen. In addition, the ALD-Al2O3 layer acts as a protective barrier, mitigating pernicious halide ion migration from the perovskite towards the hole transport interface. However, its effectiveness in preventing the infiltration of ions and additives from the hole-transport layer into perovskites remains insufficiently understood. Herein, we demonstrate the deposition of a compact ultrathin (∼0.75 nm) ALD-Al2O3 layer that conformally coats the morphology of a triple-cation perovskite layer. This promotes an effective contact of the hole transporter layer on top of the perovskite, thereby improving the charge carrier collection between these two layers. Upon systematically investigating the layer-by-layer structure of the PSC, we discovered that ALD-Al2O3 also acts as a diffusion barrier for the degraded species from the adjacent transport layer into the perovskite. In addition to these protective considerations, ALD-Al2O3 impedes the transition of crystalline perovskites to an undesired amorphous phase. Consequently, the dual functionality (i.e., enhanced contact and diffusion barrier) of the ALD-Al2O3 protection enhanced the device performance from 19.1% to 20.5%, while retaining 98% of its initial performance compared to <10% for pristine devices after 1500 h of outdoor testing under ambient conditions. Finally, this study deepens our understanding of the mechanism of ALD-Al2O3 as a two-way diffusion barrier, highlighting the multifaceted role of buffer layers in interfacial engineering for the long-term stability of PSCs. Y1 - 2025 U6 - https://doi.org/10.1039/D4EE05703A SN - 1754-5692 VL - 18 IS - 11 SP - 5250 EP - 5263 PB - Royal Society of Chemistry (RSC) CY - London ER - TY - GEN A1 - Xie, T. A1 - Rachow, F. A1 - Rakhi, undefined A1 - Berg, H. P. A1 - Höschler, K. T1 - Heat transfer analysis of a tube-in-tube steam reformer for the application of MGT-SOFC hybrid process T2 - Numerical Heat Transfer, Part A: Applications N2 - This work deals with the evaluation of a tube-in-tube reformer concept for the realization of the Micro Gas Turbine Solid Oxide Fuel Cell (MGT-SOFC) hybrid process using a semi-validated numerical model. Rigorous heat transfer analysis considering chemical reactions were performed for this concept. To validate the reforming kinetics and heat transfer mechanisms in a catalyst bed, experiments were conducted using a single reactor tube located in a temperature-controlled furnace. Different experimental conditions, such as furnace temperature and space velocity, were considered. A numerical model was replicated according to the single-tube reactor investigated and validated with the experimental results. The catalyst bed is considered as porous material with chemical reactions as internal source terms of species transport equations and energy transport equation. Since the heat transfer into the reformer tubes in the real operating environment is subject to different mechanisms (predominantly convection) than that in a furnace (predominantly thermal radiation), only the parameters on the side of the catalyst bed tuned by the single-tube experiment could be retained for the numerical model of the tube-in-tube concept, which leads to a semi-validated model. Based on this semi-validated model, the performance (such as temperature distribution, conversion rate of the products, etc.) and the applicability of a tube-in-tube reformer concept, considering the variation of boundary conditions, were investigated and evaluated. Y1 - 2024 U6 - https://doi.org/10.1080/10407782.2024.2323169 SN - 1040-7782 SP - 1 EP - 19 PB - Taylor&Francis ER - TY - GEN A1 - Buß, Lars A1 - Sulaiman, Cathy A1 - Sánchez-Barquilla, Raquel A1 - Cojocariu, Iulia A1 - Szpytma, Marcin A1 - Menteş, Tevfik Onur A1 - Locatelli, Andrea A1 - Falta, Jens A1 - Flege, Jan Ingo T1 - Rise and fall of 1T-TaS₂ : epitaxial growth of monolayer TaS₂ on Au(111) T2 - Physical review materials N2 - Monolayer tantalum disulfide epitaxially grown on Au(111) is studied in real time during molecular beam epitaxy using low-energy electron microscopy and microdiffraction. Complementary x-ray photoelectron emission microscopy provides insight into the chemical and electronic structure of the grown layers. Our study reveals a previously unreported growth mechanism where the formation of 2⁢H−TaS2 proceeds via a transient 1⁢T−TaS2 phase. The 1⁢T−TaS2 phase exhibits a significantly higher growth rate than the 2⁢H−TaS2 phase, with growth proceeding mainly in the 1T phase. By comparison with TaSe2 on Au(111), we find that this growth mechanism is common to other Ta-based transition-metal dichalcogenides on Au(111). Furthermore, we find spectroscopic evidence for the presence of charge-density-wave order in 1⁢T−TaS2 on Au(111). These findings provide perspectives on the growth dynamics and phase control of TaS2, opening up avenues for tailoring its electronic properties through substrate interaction and phase engineering. KW - LEEM KW - Low-energy electron microscopy Y1 - 2025 U6 - https://doi.org/10.1103/1bxg-yvw2 SN - 2475-9953 VL - 9 IS - 7 SP - 1 EP - 9 PB - American Physical Society (APS) CY - College Park, MD ER - TY - GEN A1 - Morales, Carlos A1 - Tschammer, Rudi A1 - Pożarowska, Emilia A1 - Kosto, Julia A1 - Villar‐Garcia, Ignacio J. A1 - Pérez‐Dieste, Virginia A1 - Favaro, Marco A1 - Starr, David E. A1 - Kapuścik, Paulina A1 - Mazur, Michał A1 - Wojcieszak, Damian A1 - Domaradzki, Jarosław A1 - Alvarado, Carlos A1 - Wenger, Christian A1 - Henkel, Karsten A1 - Flege, Jan Ingo T1 - Hydrogen sensing via heterolytic H₂ activation at room temperature by atomic layer deposited ceria T2 - ChemSusChem : chemistry, sustainability, energy, materials N2 - Ultrathin atomic layer deposited ceria films (<20 nm) are capable of H2 heterolytic activation at room temperature, undergoing a significant reduction regardless of the absolute pressure, as measured under in‐situ conditions by near ambient pressure X‐ray photoelectron spectroscopy. ALD‐ceria can gradually reduce as a function of H2 concentration under H2/O2 environments, especially for diluted mixtures below 10 %. At room temperature, this reduction is limited to the surface region, where the hydroxylation of the ceria surface induces a charge transfer towards the ceria matrix, reducing Ce4+ cations to Ce3+. Thus, ALD‐ceria replicates the expected sensing mechanism of metal oxides at low temperatures without using any noble metal decorating the oxide surface to enhance H2 dissociation. The intrinsic defects of the ALD deposit seem to play a crucial role since the post‐annealing process capable of healing these defects leads to decreased film reactivity. The sensing behavior was successfully demonstrated in sensor test structures by resistance changes towards low concentrations of H2 at low operating temperatures without using noble metals. These promising results call for combining ALD‐ceria with more conductive metal oxides, taking advantage of the charge transfer at the interface and thus modifying the depletion layer formed at the heterojunction. KW - Atomic Layer Deposition KW - Ceria KW - Hydrogen Sensing KW - X-Ray photoelectron spectroscopy KW - Raman spectroscopy KW - Resitive sensor Y1 - 2025 U6 - https://doi.org/10.1002/cssc.202402342 SN - 1864-5631 VL - 18 IS - 13 SP - 1 EP - 13 PB - Wiley-VCH CY - Weinheim ER - TY - GEN A1 - Tschammer, R. A1 - Guttmann, D. A1 - Morales, C. A1 - Henkel, K. A1 - Flege, J. I. A1 - Tiebe, C. T1 - P31 - In-situ and operando measurements for the characterization of next-generation sensor materials T2 - SMSI 2025 Conference - Sensor and Measurement Science International : proceedings N2 - In this contribution, we highlight the use of in-situ X-ray photoelectron spectroscopy and operando spectroscopic ellipsometry for the characterization of ultra-thin (<20nm) atomic layer deposited layers for the use in next-generation miniaturized sensor devices. By targeting tin oxide layers, we show how we can use these techniques to gain insights into material composition, thickness, and optical properties, thus paving the way for unraveling the correlations between material properties and sensing performance. KW - In-situ characterization KW - X-ray photoelectron spectroscopy KW - Ellipsometry KW - Tin oxide KW - Atomic Layer Deposition Y1 - 2025 UR - https://www.smsi-conference.com/assets/2025/2025-SMSI-ebooklet.pdf SN - 978-3-910600-06-5 U6 - https://doi.org/10.5162/SMSI2025/P31 SP - 292 EP - 293 PB - AMA Service GmbH CY - Wunstorf ER - TY - GEN A1 - Molenda, J. A1 - Tobola, J. A1 - Milewska, A. A1 - Budziak, A. A1 - Zając, W. A1 - Wolczko, M. A1 - Dziedzic-Kocurek, K. A1 - Nowak, M. A1 - Kałahurska, K. A1 - Imam, N. A1 - Henkel, K. A1 - Flege, J.I. A1 - Zschech, E. T1 - Unique properties of the electronic structure of alluaudite sodium iron sulfate cathode material and the impact on its electrochemical performance T2 - Acta materialia N2 - This work presents the study of the electronic structure of alluaudite-type Na2.5Fe1.75(SO4)3 and its impact on electrochemical performance as a cathode material for sodium-ion batteries (SIBs). Density functional theory calculations using the KKR-CPA method (Korringa–Kohn–Rostoker combined with the coherent potential approximation) revealed the diverse electrochemical activity of sodium ions occupying different sites within the alluaudite framework. Notably, an unprecedented contribution of sodium atoms to the overall electronic density of states near the Fermi level (dominated by Fe-d and O-p states) was observed – a feature not detected in layered transition metal oxide cathodes. A high-purity Na2.5Fe1.75(SO4)3 cathode material was synthesized via an optimized solid-state route. Using a multi-technique approach – including X-ray diffraction, scanning electron microscopy, Mössbauer spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy – the evolution of the electronic structure and electrochemical behavior during sodium (de)intercalation was comprehensively characterized, providing deep insights into the sodium storage mechanism. Operando and in situ X-ray diffraction further tracked structural changes during cycling, showing that the material undergoes a reversible amorphization at deep sodium extraction. Electrochemical tests demonstrated stable cycling with minimal capacity fade (only 2.5 % after 300 cycles at C/2), highlighting the high structural integrity and promise of this optimized cathode material. KW - Sodium-ion batteries (SIBs) KW - Alluaudite sodium iron sulfate KW - Mechanism of sodium deintercalation/intercalation KW - Crystal structure KW - Electronic structure Y1 - 2025 U6 - https://doi.org/10.1016/j.actamat.2025.121582 SN - 1359-6454 VL - 301 SP - 1 EP - 17 PB - Elsevier BV CY - Amsterdam 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 - Kalra, Amanpreet A1 - Alvarado Chavarin, Carlos A1 - Nitsch, Paul-Gregor A1 - Tschammer, Rudi A1 - Flege, Jan Ingo A1 - Ratzke, Markus A1 - Zoellner, Marvin Hartwig A1 - Schubert, Markus Andreas A1 - Wenger, Christian A1 - Fischer, Inga Anita T1 - Deposition of CeOₓ/SnOₓ-based thin films via RF magnetron sputtering for resistive gas sensing applications T2 - Physica B, Condensed matter N2 - Cerium oxide-tin oxide (CeOx/SnOx) thin films with varying Sn content were deposited using RF magnetron sputtering and investigated for hydrogen sensing applications. Structural, compositional, and morphological properties were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). Gas sensing measurements showed effective hydrogen detection at room temperature, with the sensitivity strongly influenced by Sn content and oxygen vacancy concentration. Higher Sn concentration enhanced the sensing response, which was correlated with microstructural features obtained from AFM and EDX, as well as with the presence of Ce3+ and Ce4+ oxidation states identified by XPS. This study highlights the potential of CeOx/SnOx thin films for possible back-end-of-line integration and provides proof-of-principle for room-temperature hydrogen sensing. KW - RF magnetron sputtering KW - CeOx/SnOx thin film KW - Room temperature KW - Hydrogen sensing Y1 - 2026 U6 - https://doi.org/10.1016/j.physb.2025.418098 SN - 0921-4526 VL - 723 SP - 1 EP - 7 PB - Elsevier BV CY - Amsterdam ER - TY - GEN A1 - Weichbrodt, Wiktoria A1 - Domaradzki, Jaroslaw A1 - Obstarczyk, Agata A1 - Kot, Malgorzata A1 - Flege, Jan Ingo A1 - Mazur, Michal T1 - Influence of thermal modification on the gasochromic properties of WO₃ thin films fabricated by electron beam evaporation T2 - Applied optics N2 - This paper describes the effect of post-deposition annealing on the structural and gasochromic properties of WO3 thin films deposited by electron beam evaporation and additionally decorated with a Pd catalyst layer of varying thickness. The WO3 layers were annealed at 800°C, which led to a phase transition from an amorphous to a monoclinic crystal structure, accompanied by an increase in surface roughness from 1.3 to 66 nm and the formation of a discontinuous island-like morphology with grain sizes up to 3 µm. The structural changes had a significant effect on the optical response of the layers to hydrogen. For the annealed samples, the absolute change in light transmission reached 20.2–20.9% for the 1.5 nm thick Pd catalyst and 7.7–9.2% for the 5 nm thick Pd catalyst at a wavelength of 850 nm. The corresponding optical response was 184–186% for the thin Pd layer and 353–396% for the thick Pd layer, depending on the hydrogen concentration (25–1000 ppm). The response time was reduced from 10 min at 25 ppm to < 4 min at 1000 ppm, while the recovery time to the original state in air remained below 66 s under all conditions. XPS studies confirmed the reduction of W6+ to W5+ under the influence of hydrogen and reversible transition PdO - Pd, which correlates with the observed optical changes. The results show that annealing increases crystallinity and modifies porosity, which, in combination with the Pd catalyst directly affects the kinetics and magnitude of the gasochromic response. Y1 - 2025 U6 - https://doi.org/10.1364/AO.574918 SN - 1559-128X VL - 65 IS - 5 SP - A58 EP - A67 PB - Optica Publishing Group CY - Washington, DC ER - TY - GEN A1 - Gawlińska−Nęcek, Katarzyna A1 - Dąbczyński, Paweł A1 - Nuckowski, Paweł A1 - Starowicz, Zbigniew A1 - Kot, Małgorzata A1 - Panek, Piotr A1 - Flege, Jan Ingo T1 - Crystallographic changes mediated by copper migration from hole transporting layer into CsPbBr₃ perovskite T2 - The journal of physical chemistry C N2 - Copper oxides, due to their low cost and high ambient stability, are promising candidates for use as a hole-transporting layer (HTL) in perovskite solar cells. However, it has been found that they can be very unstable in contact with organic–inorganic FAPbI3 perovskite, causing mutual chemical reactions and changing a photoactive to a nonphotoactive perovskite phase. To verify if the copper migration and the occurrence of chemical reactions are a matter of contact with a type of perovskite (organic–inorganic or fully inorganic) or the nature of copper oxides, in this work, the interface between cupric and cuprous oxides and a fully inorganic cesium lead bromide (CsPbBr3) perovskite is investigated. It is found that CsPbBr3 is not robust against copper ion migration from HTL, similarly to organic–inorganic FAPbI3; however, contrary to the previous results, they do not cause chemical reactions. Instead, crystallographic lattice shrinkage of the CsPbBr3 occurred along with the substitution of Pb2+ by copper ions. The work explains the mechanism of this phenomenon and confirms the unreliability of copper(I) oxide and copper(II) oxide as HTLs in p-i-n perovskite solar cells based on both organic–inorganic and fully inorganic lead halide perovskites. KW - Copper KW - Lattices KW - Oxides KW - Solar Cells Y1 - 2025 U6 - https://doi.org/10.1021/acs.jpcc.5c06144 SN - 1932-7447 VL - 129 IS - 43 SP - 19410 EP - 19420 PB - American Chemical Society (ACS) CY - Washington, DC 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 - TY - GEN A1 - Angrick, Christian A1 - Henriksen, Annika A1 - Edossa, Nicole A1 - Reimann, Andre A1 - Ewert, Moritz A1 - Buß, Lars A1 - Falta, Jens A1 - Flege, Jan Ingo A1 - Donath, Markus T1 - Transition metal dichalcogenide surfaces as scattering targets in spin-polarization detectors : a case study of MoS₂ T2 - Physical review B N2 - The suitability of transition metal dichalcogenides (TMDCs) for the use as scattering targets in electron spin-polarization detectors is put to a paradigmatic test: a case study of MoS₂ is performed. Therefore, the electron reflectivity, the Sherman function, and the figure of merit are measured for the following samples: a single layer of MoS₂ on Au(111) and cleaved MoS₂ single-crystal surfaces. MoS₂ offers promising features for the use in spin-polarization detection: working points with a reversed sign of the Sherman function and a long-term target stability. To overcome the low figure of merit of MoS₂, the closely-related 2D material WS₂ with higher spin-orbit interaction is proposed, which may resemble the promising features with higher Sherman function. This study demonstrates the potential suitability of 2D materials such as TMDCs as scattering targets in spin-polarization detectors. KW - Magnetism KW - Spin polarization KW - Spin-orbit coupling KW - Low-energy electron diffraction KW - Spin-resolved photoemission spectroscopy Y1 - 2025 U6 - https://doi.org/10.1103/fln2-pf6n SN - 2469-9950 VL - 112 IS - 23 SP - 1 EP - 11 PB - American Physical Society (APS) CY - College Park, Maryland ER - TY - GEN A1 - Braud, N. A1 - Wallander, H.J. A1 - Buß, L. A1 - Löfstrand, M. A1 - Blomqvist, J. A1 - Berschauer, C. A1 - Rodriguez, A. Morales A1 - Kofoed, P.M. A1 - Resta, A. A1 - Krisponeit, J.-O. A1 - Schmidt, T. A1 - Lundgren, E. A1 - Flege, J.I. A1 - Falta, J. A1 - Merte, L.R. T1 - Growth, structure, and morphology of ultra-thin tin oxide phases forming on Pt₃Sn(111) single crystals upon exposure to oxygen T2 - Surface science N2 - Here we report an investigation of ultrathin tin oxide films on Pt3Sn(111) using low-energy electron microscopy (LEEM), microspot low-energy electron diffraction (𝜇-LEED), scanning tunneling microscopy (STM), surface X-ray diffraction (SXRD), and high-resolution X-ray photoelectron spectroscopy (XPS). Oxidation at ∼390–410 ◦C produces triangular, two-dimensional oxide islands that nucleate rapidly and exhibit self-limited lateral growth, attributed to limited Sn diffusion from the subsurface of the crystal. 𝜇-LEED shows that the initially formed (4 × 4) Sn oxide is subsequently converted to a more oxygen-rich (2 × 2𝑛) ‘‘stripe’’ phase. At 630 ◦C, enhanced Sn mobility enables a closed (4 × 4) film. The (2 × 2𝑛) phase is shown to consist of a (2 × 2) Sn lattice modulated by 1D stripe defects with spacings of 𝑛 = 4–6 atomic rows; LEED and SXRD measurements show diffraction features corresponding to this striped superstructure. The two oxides can be distinguished in XPS by their O 1s lineshapes: the (4 × 4) phase shows a clear doublet attributable to distinct O species, whereas the (2 × 2𝑛) phase exhibits a broader envelope consistent with a distribution of O coordination environments. The Sn 3d5∕2 spectra are similar for both phases, reflecting closely related Sn bonding motifs. The spectra are consistent with those of previous near-ambient-pressure XPS measurements, suggesting that the surface oxides forming under CO oxidation conditions are similar to those studied here. KW - Tin oxide KW - Platinum-tin KW - LEEM KW - STM KW - SnOx KW - SXRD Y1 - 2026 U6 - https://doi.org/10.1016/j.susc.2025.122927 SN - 0039-6028 SN - 1879-2758 VL - 767 SP - 1 EP - 8 PB - Elsevier BV CY - Amsterdam ER - TY - GEN A1 - Verma, Rakhi A1 - Günther, Vivien A1 - Charlafti, Evgenia A1 - Rachow, Fabian A1 - Giri, Binod Raj A1 - Hemaizia, Abdelkader A1 - Thévenin, Dominique A1 - Flege, Jan Ingo A1 - Mauss, Fabian T1 - Development of detailed surface reaction mechanism for methanation process based on experiments T2 - Proceedings in applied mathematics and mechanics : PAMM N2 - The pressure to reduce greenhouse gas emissions is growing, which demands new and innovative technologies to produce mobile as well as stationary energy. The methanation offers a pathway to reduce greenhouse gas emissions by directly converting to . This also plays a crucial role in “power‐to‐gas” (P2G) technologies by providing an approach to store excess renewable energy in the form of methane in an existing natural gas infrastructure. However, methanation is a complex process due to its exothermic nature, interaction of the gas species with the catalyst, and possible catalyst degradation. Therefore, a deeper understanding is required for the methanation reaction, its different reaction pathways, and side reactions. In this work, we aim to understand the direct production of synthetic natural gas from and in a Sabatier process with the help of experiments over a Ni/ catalyst. A detailed surface reaction mechanism is developed to extend the study numerically by validating the simulation results with the experimental data. A one‐dimensional model, LOGEcat, based on a single‐channel catalyst model, is used for kinetic modeling. Experiments as well as simulations have been performed at various conditions, such as temperature variation and dilution to the inlet composition. We have successfully captured the experimental trends using the kinetic model developed for the conditions considered for the analysis. Y1 - 2026 U6 - https://doi.org/10.1002/pamm.70061 SN - 1617-7061 VL - 26 IS - 1 SP - 1 EP - 6 PB - Wiley CY - Weinheim 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 - TY - GEN A1 - Kapuścik, Paulina A1 - Domaradzki, Jarosław A1 - Obstarczyk, Agata A1 - Kot, Małgorzata A1 - Flege, Jan Ingo A1 - Keel, Emma A1 - Gibson, Des A1 - Wojcieszak, Damian T1 - Correlation between electron beam evaporation conditions and sensor response of cerium oxide coatings T2 - International journal of hydrogen energy N2 - Cerium oxide thin films were prepared by electron beam evaporation (EBE) under three deposition conditions: standard process, substrate heating at 200 °C, and ion beam assisted deposition (IBAD). The high optical transparency of the PVD-prepared coatings enables integration with transparent microelectronic devices, an aspect seldom explored in ceria-based gas sensors. Raman and optical analyses revealed various levels of oxygen vacancy-related defects in all films. Gas sensing measurements of the Pd/CeOx structures were correlated with their structural and electronic characteristics, including changes in Ce4+/Ce3+ ratios and band alignment during exposure to reducing gases, providing insight into the redox-driven sensing mechanism. All structures exhibit high ethanol sensitivity, while the highest response achieved for the films deposited with substrate heating and IBAD is consistent with their larger defect density and modified morphology. These findings demonstrate that tailoring EBE conditions provides an effective route to optimize CeOx thin films for improved gas sensing performance. KW - Cerium oxide KW - Thin film KW - Electron beam evaporation KW - Ion beam assisted deposition KW - Gas sensing Y1 - 2026 U6 - https://doi.org/10.1016/j.ijhydene.2026.154101 SN - 0360-3199 VL - 220 PB - Elsevier BV CY - Amsterdam ER -