Influence of film thickness, substrate temperature and nano-structural changes on the optical properties of UHV deposited Ti thin films

Titanium films of different thicknesses ranging from 18 to 210 nm were deposited on glass substrates, at different substrate temperatures (313 to 600 K) under UHV conditions. Their optical properties were measured by spectrophotometry in the spectral range of 200–2500 nm. The optical functions were obtained from the Kramers–Kronig analysis of the reflectivity curves. The effective medium approximation (EMA) analysis was employed to establish the relationship between the structure zone model (SZM) and EMA predictions. There was good agreement between SZM as a function of substrate temperature and film thickness and the values of volume fraction of voids was obtained from EMA analysis. The gettering property of Ti can play an important role in the nano-structure of the film and causes variations in the optical behaviour of thin Ti films, though films were produced under UHV condition and the XRD analysis did not show a detectable amount of oxidation. The over-layer thickness was calculated to be less than 2.0 nm, using the transfer matrix method.