Ramos Aponte, Leonardo

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    Fabricación y caracterización de películas delgadas de V3O5
    (2022-12-14) Ramos Aponte, Leonardo; Rúa de la Asunción, Armando; College of Arts and Sciences - Sciences; Marrero, Pablo J.; Sánchez Quintero, Dilsom; Department of Physics; Del Pilar Albaladejo, Joselyn
    V3O5 thin films were deposited on SiO2 substrates with similar deposition conditions by dc magnetron sputtering. Electrical properties of the thin films show differences in the resistivity values as a function of temperature in comparison with crystals values previously reported. A thermal treatment was applied after deposition under oxygen and temperature at equilibrium conditions. This was done in order to improve stoichiometry in the thin films and make the material reproducible with similar electrical properties. X-ray diffraction was used to investigate structural properties. Diffraction peaks were obtained in crystallographic planes, corresponding to the monoclinic structure of V3O5. An atomic force microscope was used to examine the morphology of the thin films. The grain size of the thin films were similar, but after annealing, the grain size increased as thermal treatment time increased. Electrical properties were studied using the Van der Pauw technique at temperatures ranging from 300 to 500 K. A metal-insulator transition was observed near 425 K. Resistivity values differed from those previously reported in bulk. This behavior can be attributed to deviations in stoichiometry of the material due to sputtering process variables that cannot be controlled. Thermal treatment was used to correct the deviations (1, 2 and 3 hours). The structural properties after annealing were also investigated. Peaks associated with V3O5 were found. The atomic force microscope measurements show microcrystals with grain sizes of approximately 4 μm for the thin films after 3 hours. Thin films after one and two hours of annealing had uniform grain distribution and grain sizes of 1-2 μm, respectively. Electrical properties for the thin films after annealing revealed a metal-insulator transition near 430 K and comparable resistivity values to the previously reported material in bulk. To calculate the transition temperature in the thermally treated thin films, an infrared transmittance technique was used. The transition temperature of the film after 3 hours of thermal treatment was 408 K, while for the thin films after 2 and 3 hours of thermal treatment was 413 K and 411 K, respectively. Differences in the transition temperature values through Van der Pauw technique and transmittance measurements were attributed to poor calibration in the percentage of transmittance. Finally, Raman Spectroscopy was used to study vibration modes in the V3O5 particles as a function of temperature. As the material heats up and approaches the transition temperature, the presence of a smooth mode and suppression of some Raman lines was observed. Furthermore, it can be established that some lines of Raman spectrum in microcrystals are weak, while in thin films are quite intense. This information may allow to extract the behavior of the transformation of the lattice network in the material.