TY - CHAP A1 - Kot, Małgorzata A1 - Naumann, Franziska A1 - Garain, Samiran A1 - Poźarowska, Emilia A1 - Gargouri, Hassan A1 - Henkel, Karsten A1 - Schmeißer, Dieter T1 - Aluminum nitride films prepared by plasma atomic layer deposition using different plasma sources T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Band 53,3 N2 - Aluminum nitride (AlN) thin films are promising for versatile applications in optoelectronics, electronics, piezoelectrics, and acoustics due to their remarkable properties such as wide band gap, high dielectric constant, low electrical conductivity, good piezoelectric coefficient and high ultrasonic velocity. We present a comparative study of AlN films grown by plasma-enhanced atomic layer deposition at 350°C silicon wafers in the SENTECH SI ALD LL system using TMA and NH3 where either a capacitively coupled plasma (CCP) or a direct PTSA (planar triple spiral antenna) source was applied. The films were characterized by ellipsometry, XPS and electrical measurements. The layer properties are discussed concerning the varied ALD process parameters. In general, the process using the direct PTSA source delivered films with higher refractive index and better homogeneity over the wafer achieving also higher growth rates per cycle (GPC) in reduced total cycle durations. Films with refractive index in the range of 2.05 and permittivity around 8 could be realized with a GPC of 1.54 Å/cycle. KW - Aluminium nitride KW - plasma-enhanced atomic layer deposition (PEALD) KW - ellispsometry KW - field emission scanning electron microscopy KW - atomic force microscopy KW - X-ray photoelectron spectroscopy KW - electrical characterization Y1 - 2018 SN - 0420-0195 SP - S. 170 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Kot, Małgorzata A1 - Henkel, Karsten A1 - Naumann, Franziska A1 - Gargouri, Hassan A1 - Tarnawska, Lidia Lupina A1 - Wilker, Viola A1 - Kus, Peter A1 - Pożarowska, Emilia A1 - Garain, Samiran A1 - Rouissi, Zied A1 - Schmeißer, Dieter T1 - Comparison of plasma-enhanced atomic layer deposition AlN films prepared with different plasma sources T2 - Journal of Vacuum Science and Technology A N2 - A comparative study of thin aluminum nitride (AlN) films deposited by plasma-enhanced atomic layer deposition in the SENTECH SI ALD LL system applying either a direct inductively coupled plasma (ICP) or an indirect capacitively coupled plasma (CCP) source is presented. The films prepared with the ICP source (based on a planar triple spiral antenna) exhibit improved properties concerning the growth rate per cycle, total cycle duration, homogeneity, refractive index, fixed and mobile electrical charges, and residual oxygen content compared to the CCP source, where the comparison is based on the applied plasma power of 200 W. The increase of the plasma power to 600 W in the ICP process significantly reduces the residual oxygen content and enhances the electrical breakdown field. The AlN layers grown under these conditions, with a growth rate per cycle of 1.54 Å/cycle, contain residual oxygen and carbon concentrations of about 10% and 4%, respectively, and possess a refractive index of 2.07 (at 632.8 nm). KW - Plamsa-enhanced atomic layer deposition (PEALD) KW - inductively coupled KW - capacitively coupled KW - plamsa source KW - ellipsometry KW - X-ray photoelectron spectroscopy (XPS) KW - X-ray diffraction (XRD) KW - Field emission scanning electron microscopy (FESEM) KW - capacitance-voltage (CV) KW - atomic force microscopy Y1 - 2019 U6 - https://doi.org/10.1116/1.5079628 SN - 0734-2101 SN - 1520-8559 VL - 37 IS - 2 ER - TY - GEN A1 - Mahmoodinezhad, Ali A1 - Pożarowska, Emilia A1 - Henkel, Karsten A1 - Schmeißer, Dieter A1 - Flege, Jan Ingo T1 - Depth profiling of PEALD-AlN films based on Al2p XPS peak decomposition T2 - Verhandlungen der DPG N2 - AlN has remarkable properties (wide band gap, low electrical and thermal conductivity, high dielectric constant, piezoelectricity) and is attractive for (opto)electronic and sensor applications. However, high oxygen content within nitride films is always a critical issue due to the thermodynamically favorable oxidation against nitridation resulting in deteriorated materials properties. In order to clarify whether the oxidation is a surface-limited or a bulk process elemental depth profiling is essential. In this work XPS in combination with Ar+ sputtering is applied to carry out depth profiling of AlN films prepared by plasma-enhanced atomic layer deposition using different parameters (plasma source, power and pulse duration). Particularly, the Al2p core levels are analyzed where the signals are decomposed into four components, representing weaker contributions of pure AlN and aluminum oxide phases as well as stronger signals of mixed oxygen-rich and nitrogen-rich phases. After sputtering (providing access to the deeper part of the film) the pure AlN phase content increases while the pure aluminum oxide content stays relatively constant. These issues are discussed with regard to the preparation parameters employed and accompanying XRD and electrical measurements. KW - X-Ray photoelectron spectroscopy (XPS) KW - peak decomposition KW - plasma enhanced atomic layer deposition (PEALD) KW - aluminium nitride (AlN) Y1 - 2019 UR - https://www.dpg-verhandlungen.de/year/2019/conference/regensburg/part/ds/session/14/contribution/25 SN - 0420-0195 SP - 157 EP - 157 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Pozarowska, Emilia A1 - Morales, Carlos A1 - Flege, Jan Ingo T1 - Growth of samarium thin films and subsequent oxidation on polycrystalline copper T2 - Verhandlungen der DPG - SurfaceScience21 N2 - The growth of samaria thin films on copper sheets has been chemically studied by in situ X-ray photoelectron spectroscopy (XPS). The early stages of growth (0.1-14 ML) were studied by consecutive evaporations of Sm by chemical vapor deposition followed by XPS measurements. Subsequently, samaria films of different thicknesses, namely 0.1, 1, and 14 ML, were oxidized at room temperature (RT). The evolution of the sample morphology was determined through inelastic peak shape analysis (IPSA) using the QUASES software as an indirect method to study the relationship between Sm oxidation state and its surface arrangement. Our results show that samarium grows as 2D islands up to 2ML, which is followed by 3D growth. Chemical analysis indicates that at low coverages (<0.5ML) Sm is already oxidized, leading to the appearance of Sm3+ as the only oxidation state. The increase in the intensity of the O1s peak with time and the absence of spectral changes in the Cu2p and LMM Auger (substrate) indicate that the transformation is mainly due to adventitious oxidation of the layer. With further deposition at RT the metallic state Sm0 appears at higher coverages, which is readily postoxidized by subsequent exposure to molecular oxygen, leading to complete oxidation. No intermediate oxidation states (Sm2+) were observed, in contrast to the reported prevalence of Sm2+ on single crystal surfaces during the early stages of growth. KW - in-situ X-ray photoelectron spectroscopy (XPS) KW - samarium oxide KW - samarium oxidation Y1 - 2021 UR - https://www.dpg-verhandlungen.de/year/2021/conference/surfacescience/part/o/session/18/contribution/2 VL - 2021 PB - Deutsche Physikalische Gesellschaft e.V. CY - Bad Honnef 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 - 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 - 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 - Kot, Małgorzata A1 - Gawlińska‐Nęcek, Katarzyna A1 - Pożarowska, Emilia A1 - Henkel, Karsten A1 - Schmeißer, Dieter T1 - Photosensitivity and carrier densities of perovskite solar absorbers T2 - Advanced science N2 - Dark and light current–voltage characteristics of perovskite solar absorbers are analyzed in terms of their carrier densities. The analysis reveals p‐type large polarons as a dominant carrier type in the investigated perovskite solar cells. The mechanism causing photosensitivity is attributed to the dissociation (and pairing) of bipolarons to large polarons (and vice versa) that are controlled by the internal potential Γ. As an example, the polaron concept is tested for a formamidinium lead triiodide perovskite solar cell. The individual steps of the data analysis are demonstrated and determine the ionicity factor of this perovskite film, quantify the density of the large polarons, and predict the gain and loss of photo‐induced carriers. It is deduced that a reversible light‐on/off operation can only occur when the bias voltage never exceeds a critical value of the internal potential. The results gained in this study suggest that the novel analysis can be successively applied on different hybrid perovskite materials, too. KW - Bipolarons KW - Ionicity factor KW - Large polarons KW - Perovskite solar cells Y1 - 2025 UR - https://advanced.onlinelibrary.wiley.com/doi/epdf/10.1002/advs.202412711 U6 - https://doi.org/10.1002/advs.202412711 SN - 2198-3844 VL - 12 IS - 16 SP - 1 EP - 8 PB - Wiley CY - Hobken, New Jersey 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 - 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 - 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 -