Synthesis and Characterization of NbOx Thin Film

Niobium Oxides (NbOx) thin films have been deposited on silicon (100) and quartz substrates by magnetron sputtering using metallic Nb target in an optimized argon-oxygen atmosphere. To date, suitable deposition conditions for crystalline NbOx thin films by reactive sputtering techniques have not been established. Therefore, this work investigates the dependence of structure-property relations on the key deposition parameters towards establishing optimum deposition conditions for the growth of NbOx crystalline films. It is found that a substrate temperature of 720 °C, low gas pressures of 8 mtorr and a target to substrate distance of 45 mm gives NbOx thin films with good homogeneity and a high degree of crystallinity. X-Ray Diffraction (XRD) and Raman spectroscopy confirmed the tetragonal phase of NbO2 and orthorhombic phase of Nb2O5 for similar deposition temperatures. Scanning Electron Microscopy (SEM) observations indicate that NbO2 has a unique nanoslice structure while Nb2O5 has a flake-like structure. Effect of post deposition annealing on the structural properties are also investigated in this dissertation. It is found that structural changes in NbO2 samples are prominent after annealing in air or Ar atmosphere. In contrast, well crystalline Nb2O5 samples do not show significant changes after annealing in air atmosphere. However, amorphous Nb2O5 can be transformed to tetragonal NbO2 after annealing in Ar atmosphere (reduction). The electrical conductivity and optical transmittance of the films have been investigated and found to be dependent on the oxygen gas content; the conductivity increases, and the optical transmittance decreases with increasing O2 gas content. Optical constants of the films were calculated by fitting model calculations to experimental transmittance data using the modified Swanepoel technique. The nanohardness and stress in the films were measured by nanoindentation and an optical profilometer, respectively. Nano hardness and stress in the film show no large dependence on the oxygen gas content except at high oxygen gas content. V being one of the prominent transition metals, is doped with NbO2 to evaluate the structural variations and the optical transmittance. It is found that higher sputtering power of V is required to be doped with NbO2 and V contents have less effect on optical transmittance of NbO2