Investigation of structural and optical properties of oblique angle sputter deposited barium strontium titanate nanostructures

Oblique angle sputtered Ba_0.5Sr_0.5TiO₃ (BST) nanotextured films were characterized with attention to their optical and structural properties. The optical band gap values included a low value of 2.82 eV for the sample sputtered at 75˚ oblique angle and a high value of 3.65 eV for the sample sputtered at 0˚. Refractive index at the wavelength of 400 nm increased from 1.377 to 2.320 with increasing oblique angle. X-ray diffraction studies revealed polycrystalline nature of deposited films exhibiting perovskite structure. Williamson-Hall analysis showed that the average crystallite sizes increased with increasing oblique angle for the samples deposited using collimator in deposition process. Atomic force microscopy showed that the surface roughness increased from 0.143 nm to 3.143 nm by increasing oblique angle. The dependence of optical band gap, refractive index, thickness, roughness, crystallite size, strain, and surface morphology on oblique angle was investigated. (paper)