Structural and optical properties of Ti oxide cluster-assembled films prepared by plasma-gas-condensation

Ti and Ti oxide cluster-assembled films have been prepared using a plasma-gas-condensation apparatus. Transmission electron microscopy and electron diffraction measurement indicates that their structures vary from a face-centered-cubic (fcc) Ti phase, via an NaCl-type TiOx phase, to an amorphous and rutile-type TiO2 mixture phase with increasing the O2 flow rate in the Ar/He gas mixture. Cluster shapes are spherical for the fcc phase, cubic for the NaCl-type, and spherical for the amorphous and rutile-type mixture, while the cluster size monotonically decreases with increasing O2 flow rate. The Ti and Ti oxide cluster-assembled films have a sooty appearance, showing a very porous morphology in the scanning electron microscopy images. The electrical resistivity dramatically increases between RO2=0.065 and 0.075 sccm, while the optical transmittance spectra in the visible wavelength range rapidly increases between RO2=0.1 and 0.12 sccm, well reflecting the structure variations in these Ti and Ti oxide cluster-assembled films.