Verbel, Camilo

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    Deposition and characterization of thin films of vanadium dioxide
    (2019-07-09) Verbel, Camilo; Rúa-de la Asunción, Armando; College of Arts and Sciences - Sciences; Fernandez, Felix E.; Marrero, Pablo J.; Department of Physics; Gutierrez, Gustavo
    In this work, thin films of VO2 and V2O3, were deposited on glass (SiO2) and TiO2 (001) substrates, by D.C. magnetron sputtering, in order to study their structural, electrical, optical and morphological properties. In addition, a thermal treatment was performed on these films under pressure and temperature conditions where VO2 is stable, with the purpose of bringing sample composition close to the correct stoichiometry of this compound. In the same manner, transformation of the V2O3 samples into VO2 was tested. A way to reduce the transition temperature of VO2 to room temperature is through the application of strain. An analogy for this is to grow VO2 in RuO2, because RuO2 has a similar structure to that of this vanadium oxide. To study this effect, RuO2 films were grown on SiO2 and TiO2 (001) substrates and the properties mentioned above were studied. In the study of structural properties using the X-ray diffraction technique, characteristic peaks of the monoclinic structure of the M1 phase of VO2 were observed. The formation of the rhombohedral structure of V2O3 and the tetragonal structure of RuO2 was also determined. In RuO2 its epitaxial growth on TiO2 (001) was confirmed. After carrying out the heat treatment of the VO2 films, it was found that diffraction peaks were close to those reported for the bulk material, showing an improvement in their structural properties. In the case of V2O3 films after the heat treatment, characteristic peaks of the M1 phase of VO2 were found which confirm that there was an oxidation of V2O3 to VO2. The morphology of the films was studied by atomic force microscopy. It was observed that VO2 and V2O3 films showed a slight increase in grain size and a relatively smooth surface after heat treatment. The optical properties were studied by the percentage change in transmittance as a function of temperature, using a laser with wavelength in the infrared. The study of electrical properties was carried out using the Van der Pauw technique. Both, in the optical and electrical properties, it was observed that when the VO2 films were deposited under the same nominal conditions they showed differences in their properties. These changes can be attributed to small variations in the material's stoichiometry.