TY - GEN A1 - Morales, Carlos A1 - Leinen, Dietmar A1 - Flores, Eduardo A1 - Muñoz-Cortes, Esmeralda A1 - Leardini, Fabrice A1 - Ares, José Ramón A1 - Flege, Jan Ingo A1 - Soriano, Leonardo A1 - Ferrer, Isabel J. A1 - Sanchez, Carlos T1 - Imaging the Kirkendall effect in pyrite (FeS2) thin films: Cross-sectional microstructure and chemical features T2 - Acta Materialia N2 - This investigation provides novel data on the structure and chemical composition of pyrite thin films and new hints concerning their formation mechanism. From TEM-HAADF data, it has been found that the films are composed of two different layers: one is very compact and the other one is quite porous with many voids separating a few groups of grains. This porous layer is always in direct contact with the substrate, and its thickness is quite similar to that of the original Fe film. The average size of pyrite grains is equal in both layers, what suggests that the same process is responsible for their formation. Concentration profiles of sulfur, iron and some impurities (mainly sodium and oxygen from the glass substrate) through both layers are given in this work, and thus chemical inhomogeneities of the films are proved by the obtained stoichiometric ratios (S/Fe). Moreover, Na from sodalime glass substrates mainly accumulates at the pyrite grain boundaries and barely dopes them. The obtained results support the hypothesis that the iron sulfuration process essentially induces the diffusion of iron atoms, what leads to the porous layer formation as a manifestation of the Kirkendall Effect. Therefore, it seems that the same mechanisms that operate in the synthesis of surface hollow structures at the nanoscale are also active in the formation of pyrite thin films ranging from several tens to hundreds of nanometers. KW - Pyrite KW - Transmission electron microscopy (TEM) KW - Cross-section KW - Kirkendall effect KW - Sodium doping Y1 - 2021 U6 - https://doi.org/10.1016/j.actamat.2020.116582 SN - 1359-6454 SN - 1873-2453 VL - 205 ER - TY - GEN A1 - Morales, Carlos A1 - Leinen, Dietmar A1 - Campo, Adolfo del A1 - Ares, José Ramón A1 - Sánchez, Carlos A1 - Flege, Jan Ingo A1 - Gutiérrez, Alejandro A1 - Prieto, Pilar A1 - Soriano, Leonardo T1 - Growth and characterization of ZnO thin films at low temperatures: from room temperature to -120 °C T2 - Journal of Alloys and Compounds N2 - ZnO thin films have been grown by e-beam evaporation in the range from room temperature to − 120 °C on two types of substrates, Al2O3 (0001) and Si (100). Although the ZnO/Al2O3 system has been thoroughly characterized, including optical and electrical techniques, the morphological, structural and chemical properties show no significant differences between both substrates. Thus, the general features of the ZnO growth mode at low temperature can be generalized. The relatively low growth temperatures reduce the diffusion of atoms at the surface, which leads to morphological and chemical changes. As the temperature decreases, the growth mode changes from a van der Drift model to a gradual bilayer system composed of an interfacial layer in contact with the substrate and a second columnar-based layer. This second well-ordered film disappears for the lowest temperatures while a Zn-rich interface in contact with the substrate emerges. Precisely from this interface, Zn-rich whiskers develop under the ZnO film and cause the loss of adhesion at temperatures below − 100 °C. These extreme temperatures also affect the crystal size, lattice strain, and total amount of oxygen vacancies. The behavior of the optical and electrical properties in terms of band gap, transparency, electrical resistivity, and Seebeck coefficient is discussed in the light of structural and chemical characterization. Samples grown at 0 °C exhibit an enhanced transmittance compared to those grown at room temperature while preserving similar electrical resistivity values and natural n-type doping. These results open a promising route to enhance ZnO films properties below the typical high temperature window. KW - zinc oxide (ZnO) KW - thin films KW - morphology KW - scanning electron microscopy (SEM) KW - DRX KW - optical properties KW - electrical properties Y1 - 2021 U6 - https://doi.org/10.1016/j.jallcom.2021.161056 SN - 0925-8388 SN - 1873-4669 VL - 884 ER - TY - GEN A1 - Morales, Carlos A1 - Pascual, Antonio A1 - Leinen, Dietmar A1 - Flores, Eduardo A1 - Muñoz-Cortes, Esmeralda A1 - Leardini, Fabrice A1 - Ares, José Ramón A1 - Flege, Jan Ingo A1 - Soriano, Leonardo A1 - Ferrer, Isabel J. A1 - Sanchez, Carlos T1 - Reaction Mechanism and Kinetic Model of Fe Thin Film Transformation into Monosulfides (FeS): First Step of the Fe Films Sulfuration Process into Pyrite T2 - The Journal of Physical Chemistry C N2 - The sulfuration of metallic iron layers into pyrite (FeS2) is preceded by an initial stage characterized by the iron transformation into monosulfide, which acts as a precursor of the disulfide. This work presents a comprehensive reaction and kinetic model of the sulfuration reaction of metallic iron thin films into monosulfides when a molecular sulfur (S2) atmosphere is used. By slowing down the sulfuration reaction, we have been able to follow in situ the evolution of the transport properties (electrical resistivity and Seebeck coefficient) of the Fe films during their sulfuration reaction to monosulfides. We show that two different stages characterize this initial sulfuration: (1) the transformation of Fe into hexagonal pyrrhotite (Fe → Fe1–xSH) and (2) a partial crystallographic transformation of this hexagonal pyrrhotite into orthorhombic pyrrhotite (Fe1–xSH → Fe1–xSO). A two-step process can explain the pyrrhotite hexagonal phase formation, being first controlled by the surface adsorption of S2 on the external sample interface (S2/pyrrhotite) and second by the diffusion of Fe atoms through the formed pyrrhotite layer. By deducing the corresponding kinetic equations in terms of the experimental parameters (S2 partial pressure and thicknesses of the layers of present species), we can explain the evolution of the electrical resistance and Seebeck coefficient of the original Fe film during its transformation into monosulfide. At the same time, the appearance of the Kirkendall effect during the monosulfide phase formation is experimental and formally justified. The comprehensive description of this first stage of the complete sulfuration process of the Fe film into pyrite provides a layout to deeply discuss the influence of these intermedium phases on the final iron disulfide film characteristics and the appearance of potential film defects related to the experimental growth conditions. KW - Fe thin films KW - sulfuration KW - kinetics KW - transport properties KW - Kirkendall effect KW - Seebeck coefficient KW - resistivity Y1 - 2022 U6 - https://doi.org/10.1021/acs.jpcc.2c02060 SN - 1932-7455 SN - 1932-7447 VL - 126 IS - 32 SP - 13870 EP - 13883 ER - TY - GEN A1 - Morales, Carlos A1 - Pascual, Antonio A1 - Leinen, Dietmar A1 - Luna-López, Gabriel A1 - Ares, Jose R. A1 - Flege, Jan Ingo A1 - Soriano, Leonardo A1 - Ferrer, Isabel J. A1 - Sanchez, Carlos T1 - Reaction Mechanism and Kinetic Model of the Transformation of Iron Monosulfide Thin Films into Pyrite Films T2 - The Journal of Physical Chemistry C N2 - This work presents a comprehensive reaction and kinetic model of the pyrite thin films formation by sulfuration of Fe monosulfides when a molecular sulfur (S2) atmosphere is used. This investigation completes the results already published on the explanation and interpretation of the sulfuration process that transforms metallic iron into pyrite. It was previously shown that the monosulfide species (i.e., orthorhombic and hexagonal pyrrhotite phases) are intermediate phases in the sulfuration reaction. Based on experimental data we now show that the sulfuration of pyrrhotite to pyrite takes place in two distinct stages: (i) conversion of orthorhombic pyrrhotite to pyrite (Fe1–xSO → FeS2) while the hexagonal pyrrhotite (Fe1–xSH) phase remains unaltered, and (ii) final transformation of hexagonal pyrrhotite to pyrite (Fe1–xSH → FeS2). Both processes occur via interstitial sulfur diffusion through the previously formed pyrrhotite layer. Consequently, the monosulfide is sulfurated at the internal Fe1–xS/FeS2 interface. The reaction mechanism at each stage has been validated using the corresponding kinetic model to fit the experimental data on time evolution of Fe1–xS and FeS2 layers thicknesses and some of the film transport properties. The concluding global reaction mechanism proposed in some of our former papers and completed here (Fe → Fe1–xS → FeS2) can explain the resulting microstructure of the pyrite films (i.e., Kirkendall effect and formation of a porous layer in the film). Simultaneously, it also justifies the presence of intrinsic defects, such as iron and sulfur vacancies, and the accumulation of interstitial sulfur at the film grain boundaries. The conductivity of pyrite films is tentatively explained using a two-band model where the changes in the Seebeck coefficient and the S/Fe ratio during the pyrite recrystallization stage can be successfully explained. KW - Sulfuration KW - Phase Transition KW - Sulfur diffusion KW - Reaction kinetics KW - Intrinsic defects KW - Seebeck coefficient Y1 - 2025 U6 - https://doi.org/10.1021/acs.jpcc.4c08227 SN - 1932-7447 VL - 129 IS - 9 SP - 4724 EP - 4737 PB - American Chemical Society (ACS) 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 - 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 - Yamada, Yuki A1 - Xue, Jin A1 - Li, Panpan A1 - Ruiz-Fernández, Susana A1 - Özdoğru, Asil Ali A1 - Sarı, Şahsenem A1 - Torres, Sergio C. A1 - Hinojosa, José A. A1 - Montoro, Pedro R. A1 - AlShebli, Bedoor A1 - Bolatov, Aidos K. A1 - McGeechan, Grant J. A1 - Zloteanu, Mircea A1 - Razpurker-Apfeld, Irene A1 - Samekin, Adil A1 - Tal-Or, Nurit A1 - Tejada, Julian A1 - Freitag, Raquel A1 - Khatin-Zadeh, Omid A1 - Banaruee, Hassan A1 - Robin, Nicolas A1 - Briseño-Sanchez, Guillermo A1 - Barrera-Causil, Carlos J. A1 - Marmolejo-Ramos, Fernando T1 - Where the ‘bad’ and the ‘good’ go : a multi-lab direct replication report of Casasanto (2009, Experiment 1) T2 - Memory & Cognition N2 - Casasanto (Journal of Experimental Psychology: General, 138, 351–367, 2009) conceptualised the body-specificity hypothesis by empirically finding that right-handed people tend to associate a positive valence with the right side and a negative valence with the left side, whilst left-handed people tend to associate a positive valence with the left side and negative valence with the right side. Thus, this was the first paper that showed a body-specific space–valence mapping. These highly influential findings led to a substantial body of research and follow-up studies, which could confirm the original findings on a conceptual level. However, direct replications of the original study are scarce. Against this backdrop and given the replication crisis in psychology, we conducted a direct replication of Casasanto’s original study with 2,222 participants from 12 countries to examine the aforementioned effects in general and also in a cross-cultural comparison. Our results support Casasanto’s findings that right-handed people associate the right side with positivity and the left side with negativity and vice versa for left-handers. Y1 - 2024 U6 - https://doi.org/10.3758/s13421-024-01637-1 SN - 0090-502X VL - 2024 SP - 1 EP - 7 PB - Springer Science and Business Media LLC ER -