Growth and optical properties of chromium borate thin films

Abstract

The present study focuses on the process of fabrication of chromium borate films using e-beam evaporation technique. The growth and optical properties of CrBO₃ thin films in the thickness range of 2-5 μm deposited by e-beam evaporation on to borosilicate glass substrates is reported for the first time. All films were deposited at ambient temperature using CrB₂ as the source material. Electron diffraction studies revealed the low-temperature growth of nanocrystalline CrBO₃ films. Raman and FT-IR spectra of the films exhibit signatures of three co-ordinated boron clearly signifying the formation of the borate. The spectral transmission of CrBO₃ films shows that films of the order of 2 micron are highly transparent (≈80%) in the visible region. The refractive index at 750 nm varies from 1.6 to 1.7 and the band gap is of the order of 2.4-2.8 eV. Nanoindentation measurements performed on the films indicate that the films are soft with hardness of the order of 0.5-1 GPa.