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 - Hernández-Gómez, Cayetano A1 - Prieto, Pilar A1 - Morales, Carlos A1 - Serrano, Aida A1 - Flege, Jan Ingo A1 - Méndez, Javier A1 - García-Pérez, Julia A1 - Granados, Daniel A1 - Soriano, Leonardo T1 - Structural defects on graphene generated by deposition of CoO: effect of electronic coupling of graphene T2 - Materials N2 - Understanding the interactions in hybrid systems based on graphene and functional oxides is crucial to the applicability of graphene in real devices. Here, we present a study of the structural defects occurring on graphene during the early stages of the growth of CoO, tailored by the electronic coupling between graphene and the substrate in which it is supported: as received pristine graphene on polycrystalline copper (coupled), cleaned in ultra-high vacuum conditions to remove oxygen contamination, and graphene transferred to SiO2/Si substrates (decoupled). The CoO growth was performed at room temperature by thermal evaporation of metallic Co under a molecular oxygen atmosphere, and the early stages of the growth were investigated. On the decoupled G/SiO2/Si samples, with an initial low crystalline quality of graphene, the formation of a CoO wetting layer is observed, identifying the Stranski-Krastanov growth mode. In contrast, on coupled G/Cu samples, the Volmer-Weber growth mechanism is observed. In both sets of samples, the oxidation of graphene is low during the early stages of growth, increasing for the larger coverages. Furthermore, structural defects are developed in the graphene lattice on both substrates during the growth of CoO, which is significantly higher on decoupled G/SiO2/Si samples mainly for higher CoO coverages. When approaching the full coverage on both substrates, the CoO islands coalesce to form a continuous CoO layer with strip-like structures with diameters ranging between 70 and 150 nm. KW - graphene KW - CoO KW - structural defects KW - X-ray photoelectronic spectroscopy KW - confocal Raman microscopy Y1 - 2024 U6 - https://doi.org/10.3390/ma17133293 SN - 1996-1944 VL - 17 IS - 13 PB - MDPI AG CY - Basel ER -