Structural, morphological, and optical properties of Ag_xO thin films deposited via obliquely angle deposition

This work reports on the optical, structural, and morphological properties of silver oxide thin films obtained by postoxidation of silver deposited previously by the thermal evaporation technique. The samples were deposited on glass substrates using the oblique angle deposition technique for different angles of incidence γ (γ=0°, 20°, 40°, 60°, 75°, and 85°). γ is defined as the angle between the particle flux and the normal to the substrate. The resulting thin films were annealed in the free air at two temperatures (300°C and 400°C). X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-visible-NIR spectrophotometer were performed to study the crystal structure, as well as the morphological and optical properties (transmittance and reflectance), of the Ag_xO samples. X-ray diffraction analysis revealed the presence of the Ag_xO phase for the silver films deposited at a high angle of incidence and for the annealing temperature 300°C. In contrast, the diffractograms of the silver films annealed at 400°C show an amorphous behavior. Optical results indicated that the direct band gap energy increases pursuant to increasing the angle of incidence γ. The absorption coefficients of Ag_xO thin films were found to be in the range of 10³–10⁵ cm⁻¹. Additionally, we determined the birefringence for the layers annealed at 400°C and found that the highest value of birefringence is obtained corresponding to the angle of incidence 60°. Morphological analysis indicated that the porosity increases with the angle of incidence and highlights the amorphous nature of the films, which is attributed to the columnar structure.