Structural and optical properties of γ-alumina thin films prepared by pulsed laser deposition

Preparation of gamma-alumina thin films by pulsed laser deposition from a sintered a-alumina target is investigated. The films were deposited on (100) silicon substrates at 973 K with varying oxygen partial pressures in the range 2.0 x 10(-5)-3.5 x 10(-1) mbar. X-ray diffraction results indicated that the films were polycrystalline gamma-Al2O3 with cubic structure. The films prepared in the oxygen partial pressure range 2.0 x 10(-5)-3.5 x 10(-2) mbar contained nanocrystals of sizes in the range 10-16 nm, and became amorphous at pressures >3.5 x 10(-1) mbar. Topography of the films was examined by atomic force microscopy using contact mode and it showed the formation of nanostructures. The root-mean square surface roughness of the film prepared at 2.0 x 10(-5) mbar and 3.5 x 10(-1) mbar were 1.4 nm and 3.5 nm, respectively. The thickness and optical properties were studied using ellipsometry in the energy range 1.5-5.5 eV for three different angles of incidence. The refractive index was found to decrease from 1.81 to 1.73 with the increase of oxygen partial pressures from 2.0 x 10(-5) to 3.5x10(-2) mbar. The variation in the refractive index has been found to be influenced by the microstructure of the films obtained as a function of oxygen partial pressure. (C) 2009 Elsevier B.V. All rights reserved.