Vacuum ultraviolet annealing of thin films grown by pulsed laser deposition

Abstract

The effect of a post-deposition annealing treatment in 1 bar of oxygen at moderate temperatures (<450°C) under illumination by vacuum ultraviolet (VUV) radiation emitted by an excimer lamp upon thin ZrO 2 and hydroxyapatite (HAp) films grown by the pulsed laser deposition (PLD) technique was investigated. The optical and structural properties of the films were improved by this treatment, the lower the deposition temperature and, accordingly, the poorer the initial characteristics, the more significant the improvements. The combination of these two techniques allowed us to obtain at temperatures below 350°C highly textured (020) ZrO 2 films, exhibiting optical absorption coefficients lower than 5×10 2 cm −1 and high refractive index values of around 2.25 in the visible region of the spectrum. The VUV treatment was also beneficial for the partially crystalline HAp layers containing tetracalcium phosphate and calcium oxide phases grown by the PLD technique under a low pressure oxidising atmosphere of only 10 −5 torr without any water vapours. After the VUV-assisted anneal, the crystalline structure and the stoichiometry greatly improved while the percentage of the other crystalline phases initially present was many times reduced.