Role of ion energy on growth and optical dispersion of nanocrystalline TiO2 films prepared by magnetron sputtering with ion assistance at the substrate

TiO2 films are deposited by direct current reactive magnetron sputtering with radio frequency substrate bias. Plasma ions are accelerated towards the substrate due to the negative self bias developed at the substrate. X-ray diffraction pattern reveals that the films deposited at the floating potential (-35 V) of the substrate are amorphous, and broad, low intensity rutile peaks of TiO2 are observed for the films deposited with the substrate bias (self bias in the range -40 to -100 V). A gentle ion bombardment of the growing surface improves the crystallinity of the films. The films are nanocrystalline and rutile phase is retained in the self bias range -40 to -100 V. Films are highly transparent to visible and near infrared and ultraviolet light is effectively filtered out. The optical constants are extracted by the Swanepoel method and the optical dispersion parameters are determined by employing the Wemple-DiDomenico single oscillator model. Inherent good adhesion of plasma based deposits, small crystallite size, high level of transmittance in the visible region and colorless appearance may enhance the performance of the films as optical coatings.