Physical and electrical characterization of TiO_2 particles after high temperature processing and before and after ultraviolet irradiation

摘要

In this work, rutile-phase TiO_2 particles (r-TiO_2, about 360 nm in size) are embedded within a silicon oxide matrix using different concentration ratios of r-TiO_2 with respect to SiO_2:H_2O, so that suspensions of mixed TiO_2:SiO_2 oxides were obtained and analyzed. These TiO_2:SiO_2 suspensions were deposited on previously-cleaned crystalline silicon and quartz substrates so that thin films of TiO_2:SiO_2 were obtained. All films were then exposed to relatively high-temperature thermal treatments in nitrogen and different characterization techniques were used to determine their physical and electrical properties before and after ultraviolet (UV) irradiation. Before high thermal treatment, X-ray diffraction patterns show that the main diffraction peaks for the obtained TiO_2:SiO_2 films correspond to the crystalline phase of rutile-TiO_2. Infrared analyses before and after thermal treatment show significant changes in the chemical bonding of the final films relative to the temperatures used during annealing. Also, UV-visible spectra provide a constant optical band gap for the films, independent of different TiO_2 concentrations as expected. On the other hand, atomic-force microscopy measurements before and after UV irradiation show an appreciable difference in the grain size and surface morphology of the resulting TiO_2:SiO_2 oxides annealed at 1000 ℃. Finally,photoelectrical I-V properties were obtained for all TiO_2:SiO_2 films by depositing ultrathin titanium stripes on top of the photoactive material and then, measuring the total current flowing through the metal electrode before and after UV irradiation. From these last measurements, a detectable increase in the I-V slope (lower resistance of the titanium stripe) is found for all samples during UV exposure, thus making this device to act as a simple photoresistor based on r-TiO_2 particles.