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 -