Pulsed Laser Deposition of Nanocrystal TiO_2 Films and its Optical Properties

Titanium dioxide nanocrystal films were deposited on silicon substrates using pulsed laser deposition method.The influences of substrate temperature,oxygen partial pressure and the kinds of gas on the crystal structure of TiO_2 thin films were discussed.The optical properties of films were studied by means of transmission spectra in UV-visible range,Fourier transform infrared spectra and Raman spectra.The results show that the films are high c-axis-oriented anatase and(110)oriented rutile prepared at the substrate temperature of 750℃under the oxygen and argon pressure of 5Pa, respectively.The field emission scanning electron microscopy images indicate that the TiO_2 films has a good smooth and hole-free surface which are composed of nanocrystal grains with about 35nm in diameter.And the optical properties tested show that the films are transparent in the visible range. From the transmission spectra in UV-visible range,the refractive index of the anatase and rutile TiO_2 films are determined to be about 2.3 and 2.5 at 550nm,respectively.And the optical band gaps are determined to be 3.2eV and 3.0eV for the anatase film and rutile film,respectively.