The thermal oxidation of CuS powder was examined under flow of nitrogen and dry air using thermogravimetry/differential thermal analysis. After 473 K, the oxidation of CuS occurred as a weight loss and accompanied with two overlapped exothermic peaks. The melting temperature delayed due to the formation of oxide and sulphate on the surface of the particles. X-ray diffraction revealed that the as-prepared thin films are mixed phases of hexagonal CuS, orthorhombic Cu$_2$S and orthorhombic CuSO$_4$. After annealing at 573 or 773 K, the films oxidized and new orthorhombic Cu$_8$O phase appeared, and its intensity became dominant upon increasing the temperature and time. Nanoparticles morphology was observed for as-prepared films and upon annealing the nanoparticle became more rounded and bigger. The transmittance of the as-prepared films was almost zero over the entire measured range and it increased with increase in the annealing temperature and time, whereas the reflectance decreased. Both refractive and extinction coefficient values decreased with increase in annealing temperature and annealing time, while the bandgap virtually increased. The resistivity of the as-prepared film remained nearly constant until 543 K. Above 543 K the resistivity increased sharply. Negative and positive temperature coefficients in resistivity phenomena were explored in the annealed films and they were strongly dependent on both annealing temperature and time.

In this work, the structural, morphological, electrical and optical properties of Bi$_{2–x}$Te$_3$Fe$_x$ (x = 0, 0.3 and 0.5 at%) thin films were investigated. X-ray diffraction investigations revealed the formation of hexagonal Bi$_2$Te$_3$ structure for undoped and Fe-doped films. Scanning electron microscopy observations revealed an increase in the average grain size from 20.4 to 43.5 nm with increasing Fe doping ratio from 0 to 0.5 at%. A transition from N-type conduction to P-type conduction with a decrease in carrier concentration was observed after Fe doping with 0.3 at%. Energy-dispersive X-ray spectroscopy spectra confirmed the presence of Fe in the doped films. The optical absorbance (Abs), transmittance (T%) and reflectance (R%) spectra of Bi$_{2–x}$Te$_3$Fe$_x$ films were measured in the spectral range from 200 to 2500 nm. Both T% and R% were strongly affected by Fe doping. The optical bandgap decreased from 0.26 to 0.17 eV with increasing Fe ratio from 0 to 0.5 at%. Over most of the studied wavelength range, the refractive index values increased with increasing Fe doping ratio. The optical conductivity values were mainly increased with Fe doping. The examined optical and electrical properties of Bi$_{2–x}$Te$_3$Fe$_x$ (x = 0, 0.3 and 0.5 at%) thin films may enable rapid material selection for designing certain applications such as optical coatings.