Nanostructure and photocatalytic properties of TiO2 films deposited at low temperature by pulsed PECVD

The nanostructure and photocatalytic properties of TiO2 thin films deposited by PECVD on silicon substrates were investigated. The films were grown at low temperature (< 120 degrees C) in an rf inductively coupled oxygen/titanium tetraisopropoxide plasma, in continuous and pulsed modes with different plasma-on time (via variation of the duty cycle, DC). All the films exhibit nano-columnar structures, but the reduction of plasma-on time by decreasing the duty cycle for pulsed mode leads to a more homogenous morphology with a diminished column size, and a decrease in the surface roughness. TiO2 layers containing a high amount of anatase were grown at substrate temperatures less than 100 degrees C corresponding to DC >= 40%, then the crystallization was hindered with the decrease of DC, even inducing amorphous films for DC <= 10%. Moreover, the films deposited below 100 degrees C with deposition conditions where 50% <= DC <= 75% were shown to present a high photocatalytic activity, likely due to the presence of anatase crystalline nanocolumns at the surface.