TY - GEN A1 - Gertig, Max A1 - Morales, Carlos A1 - Henkel, Karsten A1 - Flege, Jan Ingo T1 - In situ X-ray photoelectron spectroscopy study of atomic layer deposited ceria on SiO2: substrate influence on the reaction mechanism during the early stages of growth T2 - Verhandlungen der DPG N2 - Atomic layer deposition (ALD) is known to produce amorphous and defect-rich films in a layer-by-layer fashion, which can potentially give rise to unexpected material properties. In particular, ultrathin films (few monolayers) will show the highest complexity, as the substrate-material interaction will play a major role during deposition. Therefore, it is crucial to understand the early stages of growth of the ALD process to control and potentially tailor this interfacial interaction. Applying a surface science approach combined with complementary ex-situ characterization, we have studied by in-situ X-ray photoelectron spectroscopy (XPS) the early stages of ceria (CeOx) growth on SiO2 substrates deposited by thermal-ALD using Ce(thd)4/O3. Interestingly, an initial mixture of Ce3+ and Ce4+ was observed, although only Ce4+ may be expected considering the used precursor and oxidant. This fact, together with a deviation from the ideal layer-by-layer growth and a higher growth rate during the first cycles, indicates a significant influence of the substrate of the ALD reaction mechanism as well as a correlation between morphology and ceria oxidation state. KW - Atomic layer deposition (ALD) KW - X-ray photoelectron spectroscopy (XPS) KW - in-situ KW - ceria Y1 - 2024 UR - https://www.dpg-verhandlungen.de/year/2024/conference/berlin/part/o/session/67/contribution/7 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Guttmann, Dominic A1 - Riedel, Björn A1 - Sánchez-Barquilla, Raquel A1 - Morales, Carlos A1 - Flege, Jan Ingo T1 - Oxide formation and oxide/metal interaction in CeOx/Ni(111) T2 - Verhandlungen der DPG N2 - Ni/ceria catalysts exhibit a high activity for methane to methanol conversion, making them very promising for applications within a sustainable economy. Possibly, their activity may be strongly enhanced due to the facile exchange between Ce4+ and Ce3+ states, with the latter likely responsible for activating O-H and C-H bonds. Here, we aim to unravel the complex metal-oxide interactions in the inverse CeOx/Ni(111) system under oxidizing and reducing environments. Using low-energy electron diffraction (LEED) we find that the CeOx(111) grown by reactive molecular beam epitaxy preferentially aligns with the main directions of the Ni(111) substrate or is azimuthally rotated by ±10°. By using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS), we find that less NiO is formed during deposition of CeOx than when it is held without ceria at the same conditions (O2 partial pressure and temperature). Finally, we observe a complex behavior of the cerium and nickel oxidation states when exposing the system to O2 or H2 atmospheres. KW - Low-energy electron diffraction (LEED) KW - ceria KW - X-ray photoelectron spectroscopy (XPS) KW - ultraviolet photoelectron spectroscopy (UPS) KW - oxidation states Y1 - 2024 UR - https://www.dpg-verhandlungen.de/year/2024/conference/berlin/part/o/session/33/contribution/10 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Zia, Waqas A1 - Malekshahi Byranvand, Mahdi A1 - Rudolph, Toby A1 - Rai, Monika A1 - Kot, Małgorzata A1 - Das, Chittaranjan A1 - Kedia, Mayank A1 - Zohdi, Mohammadreza A1 - Zuo, Weiwei A1 - Yeddu, Vishal A1 - Saidaminov, Makhsud I. A1 - Flege, Jan Ingo A1 - Kirchartz, Thomas A1 - Saliba, Michael T1 - MAPbCl3 Light Absorber for Highest Voltage Perovskite Solar Cells T2 - ACS Energy Letters N2 - Perovskite solar cells (PSCs) excel in achieving high open-circuit voltages (VOC) for narrow bandgaps (∼1.6 eV) but face challenges with wide-bandgap perovskites, like methylammonium lead trichloride (MAPbCl3) with a 3.03 eV bandgap. These materials are transparent in visible absorbing ultraviolet (UV) light. However, achieving uniform film crystallization remains a hurdle. Here, we enhance MAPbCl3 crystallization by manipulating annealing atmospheres (nitrogen, air, and MACl vapor). Excess MACl vapor improves surface coverage, which is crucial for film stability. We demonstrate that the microstructure of the perovskite film, including surface morphology, grain boundaries, and interfaces, can affect the photovoltaic properties. The subsequently obtained VOC of 1.78 V is the highest recorded for single-junction PSCs to the best of our knowledge. Surprisingly, the conventional hole-transport layer spiro-OMeTAD, optimized for narrow bandgaps, sustains such high voltages. Photoluminescence measurements reveal a trap-assisted recombination peak at 1.65 eV, indicating deep traps as significant to voltage loss in MAPbCl3. KW - Perovskite solar cells KW - methylammonium lead trichloride (MAPbCl3) KW - uniform film crystallization KW - manipulation of annealing atmospheres KW - trap-assisted recombination KW - microstructure Y1 - 2024 U6 - https://doi.org/10.1021/acsenergylett.3c02777 SN - 2380-8195 VL - 9 SP - 1017 EP - 1024 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 - Nitsch, Paul-G. A1 - Ratzke, Markus A1 - Pozarowska, Emilia A1 - Flege, Jan Ingo A1 - Alvarado Chavarin, Carlos A1 - Wenger, Christian A1 - Fischer, Inga Anita T1 - Deposition of reduced ceria thin films by reactive magnetron sputtering for the development of a resistive gas sensor T2 - Verhandlungen der DPG, Berlin 2024 N2 - The use of cerium oxide for hydrogen sensing is limited by the low electrical conductivity of layers deposited from a ceria target. To increase the electrical conductivity, partially reduced cerium oxide layers were obtained from a metallic cerium target by reactive magnetron sputtering. The proportions of the oxidation states Ce3+, present in reduced species, and Ce4+, present in fully oxidized species, were determined by ex-situ XPS. For electrical characterization, films were deposited on planarized tungsten finger electrodes. IV curves were measured over several days to investigate possible influences of oxygen and humidity on electrical conductivity. The morphological stability of the layers under ambient conditions was investigated by microscopical methods. The XPS results show a significant amount of Ce3+ in the layers. The electrical conductivity of as-grown samples is several orders of magnitude higher than that of samples grown from a ceria target. However, the conductivity decreases over time, indicating an oxidation of the layers. The surface morphology of the samples was found to be changing drastically within days, leading to partial delamination. KW - ceria KW - metalic cerium target KW - electrical conductivity KW - X-ray photoelectron spectroscopy (XPS) KW - oxidation states KW - morphology Y1 - 2024 UR - https://www.dpg-verhandlungen.de/year/2024/conference/berlin/part/ds/session/11/contribution/18 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Gawlińska-Nęcek, Katarzyna A1 - Kot, Małgorzata A1 - Starowicz, Zbigniew A1 - Jarzębska, Anna A1 - Panek, Piotr A1 - Flege, Jan Ingo T1 - Instability of Formamidinium Lead Iodide (FAPI) Deposited on a Copper Oxide Hole Transporting Layer (HTL) T2 - ACS Applied Materials & Interfaces N2 - Copper oxide appears to be a promising candidate for a hole transport layer (HTL) in emerging perovskite solar cells. Reasons for this are its good optical and electrical properties, cost-effectiveness, and high stability. However, is this really the case? In this study, we demonstrate that copper oxide, synthesized by a spray-coating method, is unstable in contact with formamidinium lead triiodide (FAPI) perovskite, leading to its decomposition. Using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible (UV–vis) spectrophotometry, we find that the entire copper oxide diffuses into and reacts with the FAPI film completely. The reaction products are an inactive yellow δ-FAPI phase, copper iodide (CuI), and an additional new phase of copper formate hydroxide (CH2CuO3) that has not been reported previously in the literature. KW - formamidinium lead iodide KW - perovskites KW - instability KW - Cu2O KW - hole transporting layer KW - phase transition Y1 - 2024 U6 - https://doi.org/10.1021/acsami.4c03440 SN - 1944-8244 VL - 16 IS - 21 SP - 27936 EP - 27943 PB - American Chemical Society (ACS) ER - TY - GEN A1 - Kapuścik, Paulina A1 - Wojcieszak, Damian A1 - Pokora, Patrycja A1 - Mańkowska, Ewa A1 - Domaradzki, Jarosław A1 - Mazur, Michał A1 - Mazur, Piotr A1 - Kosto, Yuliia A1 - Morales, Carlos A1 - Kot, Małgorzata A1 - Flege, Jan Ingo T1 - Low temperature hydrogen sensor with high sensitivity based on CeOx thin film T2 - Sensors and Actuators B: Chemical N2 - In this work, a 500 nm-thick cerium oxide thin film was prepared by electron beam evaporation. It was found that the deposition of 7 nm thick Pd catalyst was required for obtaining a sensor response to hydrogen. The Pd/CeOx sensing structure has a high response of 5000 towards 25 ppm H2 at a working temperature of 200 °C and exhibits a sensor response of 1.3 at temperatures near ambient. Furthermore, the sensing structure exhibited excellent response/recovery kinetics. The results confirm that the CeOx-based materials are a promising material for the fabrication of room-temperature hydrogen sensors. KW - Cerium oxide KW - Thin film KW - Hydrogen sensing KW - Low operating temperature Y1 - 2024 U6 - https://doi.org/10.1016/j.snb.2024.136148 SN - 0925-4005 VL - 417 PB - Elsevier BV ER - TY - GEN A1 - Kodalle, Tim A1 - Malekshahi Byranvand, Mahdi A1 - Goudreau, Meredith A1 - Das, Chittaranjan A1 - Roy, Rajarshi A1 - Kot, Małgorzata A1 - Briesenick, Simon A1 - Zohdi, Mohammadreza A1 - Rai, Monika A1 - Tamura, Nobumichi A1 - Flege, Jan Ingo A1 - Hempel, Wolfram A1 - Sutter‐Fella, Carolin M. A1 - Saliba, Michael T1 - An Integrated Deposition and Passivation Strategy for Controlled Crystallization of 2D/3D Halide Perovskite Films T2 - Advanced Materials N2 - This work introduces a simplified deposition procedure for multidimensional (2D/3D) perovskite thin films, integrating a phenethylammonium chloride (PEACl)‐treatment into the antisolvent step when forming the 3D perovskite. This simultaneous deposition and passivation strategy reduces the number of synthesis steps while simultaneously stabilizing the halide perovskite film and improving the photovoltaic performance of resulting solar cell devices to 20.8%. Using a combination of multimodal in situ and additional ex situ characterizations, it is demonstrated that the introduction of PEACl during the perovskite film formation slows down the crystal growth process, which leads to a larger average grain size and narrower grain size distribution, thus reducing carrier recombination at grain boundaries and improving the device's performance and stability. The data suggests that during annealing of the wet film, the PEACl diffuses to the surface of the film, forming hydrophobic (quasi‐)2D structures that protect the bulk of the perovskite film from humidity‐induced degradation. KW - 2D/3D perovskites KW - crystallization KW - in situ characterization KW - stability Y1 - 2024 U6 - https://doi.org/10.1002/adma.202309154 SN - 0935-9648 VL - 36 IS - 24 PB - Wiley CY - Weinheim ER - TY - GEN A1 - Kosto, Yuliia A1 - Tschammer, Rudi A1 - Morales, Carlos A1 - Henkel, Karsten A1 - Flege, Jan Ingo A1 - Ratzke, Markus A1 - Fischer, Inga Anita A1 - Costina, Ioan A1 - Alvarado Chavarin, Carlos A1 - Wenger, Christian T1 - Rational design and development of room temperature hydrogen sensors compatible with CMOS technology: a necessary step for the coming renewable hydrogen economy T2 - Proceedings of iCampus Conference Cottbus 2024 N2 - The transition towards a new, renewable energy system based on green energy vectors, such as hydrogen, requires not only direct energy conversion and storage systems, but also the development of auxiliary components, such as highly sensitive hydrogen gas sensors integrated into mass devices that operate at ambient conditions. Despite the recent advances in nanostructured metal oxide thin films in terms of simple fabrication processes and compatibility with integrated circuits, high sensitivity, and short response/recovery times usually require the use of expensive noble metals or elevated tem-peratures (>250 ºC), which results in high power consumption and poor long-term stability. This article presents the first steps of the work on developing a novel resistive hydrogen gas sensor based on ultrathin cerium oxide films, compatible with complementary metal oxide semiconductor technology and capable of operating at room temperature. Here, we show a multidisciplinary bottom-up approach combining different work areas for the sensor development, such as sensor architecture, sensing mechanism and deposition strategy of the active layer, electrical contact design depending on the desired electrical output, and fast testing under controlled environments. KW - gas sensors KW - micro-structering KW - atomic layer deposition KW - sensor platform Y1 - 2024 SN - 978-3-910600-00-3 U6 - https://doi.org/10.5162/iCCC2024/P21 SP - 182 EP - 185 PB - AMA Service GmbH CY - Wunstorf ER - TY - GEN A1 - Sanchez-Barquilla, Raquel A1 - Tschammer, Rudi A1 - Buß, Lars A1 - Morales, Carlos A1 - Flege, Jan Ingo T1 - The relation between substrate, Sm alloy, and surface sensitivity of ceria (111)- and (100)-oriented nano-islands on Ru(0001) and Cu(111) T2 - Verhandlungen der DPG N2 - Inverse oxide/metal catalysis allows achieving better catalytic performance than its traditional counterpart. For example, in cerium-based inverse catalyst systems, the Ce3+ states have been shown to be the active sites for methanol synthesis. This suggests that the activity can be enhanced by promoting those through alloying with trivalent, catalytically active rare-earth metals, as, e.g. Sm. We present low-energy and X-ray photoemission electron microscopy (LEEM/XPEEM), investigations that show how epitaxially grown (100)- and (111)-oriented CeO2 islands may be modified and/or alloyed by post-deposited metallic Sm. For the Ce1−xSmxO2−δ/Ru(0001) system, the CeO2 (111)-oriented islands undergo a structural change, concomitant with a partial conversion from Ce4+ to Ce3+. Surprisingly, for Ce1−xSmxO2−δ/Cu(111) the result is found to be face-dependent since only (100)-oriented CeOx islands were reduced whereas the (111)-oriented islands remained unaltered. Both systems have been exposed to reducing (H2) and oxidizing (CO2) conditions, resulting in higher reduction and in a complete recovery of the Ce4+ states, respectively. These unexpected results indicate a complex interaction not only between cerium and the doping element, but also an intricate interplay with the metallic substrate. KW - ceria KW - low-energy electron microscopy (LEEM) KW - X-ray photoemission electron microscopy (XPEEM) KW - samarium KW - metal substrate influence on reduction KW - orientation Y1 - 2024 UR - https://www.dpg-verhandlungen.de/year/2024/conference/berlin/part/o/session/85/contribution/6 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER -