Nano-phase titanium dioxide thin film deposited by repetitive plasma focus: Ion irradiation and annealing based phase transformation and agglomeration

摘要

We report the successful deposition of nano-phase crystalline titanium dioxide (TiO_2) thin films using a repetitive plasma focus device on silicon (Si) substrates at room temperature. The plasma focus device, fitted with solid titanium anode was operated with argon-oxygen admixture as the filling gas. X-ray diffraction (XRD) patterns of as-deposited films confirm the deposition of crystalline TiO_2 thin films having polymorphism nature; anatase and rutile, and their relative phase transition and crystallinity improvement by increasing the number of ion irradiation shots and/or annealing temperature. The crystallite sizes of the TiO_2 particulates estimated from the typical diffraction peaks are found to be approximately 8 nm and 13 nm. The weight ratios of anatase and rutile in the TiO_2 were estimated and it was revealed that anatase weight fraction was reduced by increasing the total ion irradiation and/or annealing temperature, owing to phase the transformation from anatase to rutile. Raman studies have also established the dominant presence of E_g and A_(1g) Raman active modes of the rultile phase. Scanning electron micrographs (SEM) of the as-deposited films reveal uniformly distributed nano-phase morphology over the film surface. Agglomeration of smaller TiO_2 nano-sized grains, to form bigger sized particulates, is seen to occur owing to the clustering of charged nucleates in the gas phase. The agglomeration is enhanced by increasing the number of ion irradiation shots and/or annealing temperature.