Preparation of TiO2 thin films on the inner surface of a quartz tube using atmospheric-pressure microplasma

Titanium dioxide (TiO2) thin films were prepared on the inner surface of a quartz tube, with inner and outer diameters of 1 and 3 mm, respectively, using plasma-enhanced chemical vapor deposition with titanium tetraisopropoxide and oxygen (O2) as reactants and helium as the carrier gas at atmospheric pressure. A microplasma was generated inside the tube by rf (13.56 MHz) excitation using externally attached parallel-plate electrodes. The characteristics of the deposited films were examined by scanning electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction. A typical as-deposited film had an amorphous structure with a smooth surface and was transparent. With increasing O2 concentration in the plasma gas phase, the deposited film surface was covered with a large number of TiO2 nanoparticles. However, the deposited films were a mixture of TiO2 and amorphous carbon and showed rough surface in the absence of O2 in the source gas. The effects of the O2 concentration in the plasma gas on the characteristics of the deposited TiO2 films are discussed on the basis of the analysis of the gas species generated in the plasma using optical emission spectroscopy