TY - GEN A1 - Tschammer, Rudi A1 - Kosto, Yuliia A1 - Morales, Carlos A1 - Schmickler, Marcel A1 - Henkel, Karsten A1 - Devi, Anjana A1 - Flege, Jan Ingo T1 - Atomic layer deposition of cerium oxide monitored by operando ellipsometry and in-situ X-ray photoelectron spectroscopy T2 - Verhandlungen der DPG N2 - Atomic layer deposition (ALD) has been used extensively to grow homogeneous films with excellent coverage and atomic-scale thickness control for a variety of applications. However, remaining challenges include the investigation of novel precursor-oxidant combinations for low-temperature deposition as well as unraveling the complex interplay between substrate and coating for ultrathin films. In this work, we present a detailed investigation of ultrathin cerium oxide films grown using the novel Ce(dpdmg)3 precursor with H2O and O2. Following a surface science-based approach, we have combined operando spectroscopic ellipsometry and in-situ X-ray photoelectron spectroscopy to allow rapid process optimization and determination of the complex relation between oxide stoichiometry, film thickness and ALD growth parameters, revealing a distinct dependence of inital Ce3+ content on the film thickness and choice of oxidant. This offers the possibility of adjusting the oxide properties to application requirements e.g. in gas sensing by choosing a suitable precursor-oxidant combination. KW - Atomic layer deposition (ALD) KW - ceria KW - low-temperature deposition KW - operando spectroscopic ellipsometry KW - in-situ X-ray photoelectron spectroscopy KW - film thickness KW - oxidant choice KW - cerium oxidation state Y1 - 2024 UR - https://www.dpg-verhandlungen.de/year/2024/conference/berlin/part/o/session/49/contribution/4 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - 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 - Kosto, Yuliia A1 - Kapuscik, Paulina A1 - Tschammer, Rudi A1 - Guttmann, Dominic A1 - Mankowska, Ewa A1 - Matvija, Peter A1 - Morales, Carlos A1 - Mazur, Michał A1 - Henkel, Karsten A1 - Matolinova, Iva A1 - Domaradzki, Jarosław A1 - Flege, Jan Ingo T1 - Bare and Pd-doped ceria thin films prepared by ALD and EBE for hydrogen detection T2 - Verhandlungen der DPG N2 - The need to store and use hydrogen safely as part of green economy based on renewable energy evokes a necessity to reliably detect it at ambient conditions. The majority of currently used sensors are working at elevated temperatures (200-500 °C). In this work, we demonstrate that ceria films deposited on a commercial electrode by atomic layer deposition (ALD) and electron beam evaporation (EBE) electrically respond to hydrogen (from 20 to 500 ppm) at much lower temperatures (50-200 °C). The results reveal that <1.5 nm thin Pd adlayer increases the electrical response by several orders of magnitude for both ceria films. The NAP-XPS study under changing oxidative/reductive atmospheres sheds light on the mechanism of Pd-CeOx thermal activation and the role of the deposition technique in the reactivity of the oxide. KW - Hydrogen sensor KW - Atomic layer deposition (ALD) KW - ceria KW - Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) Y1 - 2024 UR - https://www.dpg-verhandlungen.de/year/2024/conference/berlin/part/o/session/59/contribution/5 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Morales, Carlos A1 - Kosto, Yuliia A1 - Tschammer, Rudi A1 - Henkel, Karsten A1 - Flege, Jan Ingo T1 - Unraveling the effects of substrate interaction on the chemical properties of atomic layer deposited ultra-thin ceria layers T2 - Verhandlungen der DPG N2 - Atomic layer deposition (ALD) is well known to lead to amorphous and defective, non-stoichiometric films, potentially resulting in modified material properties that can also be affected by film/substrate interaction in the case of ultra-thin growths. For example, the formation, diffusion, and recovery of oxygen vacancies can be favored in disordered, reducible metal oxides compared to more ordered deposits, whereas interdiffusion processes can critically affect the film/substrate interface region. These effects have extensively been studied for thin thermal-ALD ceria films (below 15 nm) by combining in-situ and ex-situ characterization techniques in our lab and at synchrotron radiation facilities. While using alumina or silica substrates modifies the initial growth rate, Ce3+/Ce4+ ratio, and ceria morphology, the formation of different species at the interface affects its reactivity. Interestingly, the experiments have shown high reducibility of ALD-ceria ultrathin films on silica for very low hydrogen concentrations, even at room temperature, whereas for alumina substrates the formation of aluminates at the interface prevents further oxidation. Moreover, the comparison with more ordered films indicates a key role of the defective structure of ALD films in Ce3+/Ce4+ conversion. KW - Atomic layer deposition (ALD) KW - ceria KW - interface reaction KW - morphology KW - reducibility KW - hydrogen detection Y1 - 2024 UR - https://www.dpg-verhandlungen.de/year/2024/conference/berlin/part/o/session/49/contribution/8 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER -