OPTICAL OSCILLATOR-STRENGTHS AND QUANTUM-MECHANICS MATRIX-ELEMENTS OF WO(3) POLYCRYSTALLINE THIN-FILMS

Polycrystalline films of WO3 were prepared by chemical vapour deposition techniques. Optical reflection and transmission and mass densities of these films were measured. The optical properties of WO3 films are discussed in terms of the single average excitation energy, E0, the normalized coordinate matrix element, x2, the normalized macroscopic oscillator strength, f, and the bond packing factor, B. With the aid of the effective medium theory, it is shown that in inhomogeneous WO3 films these properties are equally related to the microstructure, i.e., the volume fractions of crystalline, of amorphous material and of voids contained in the film. In general, the presence of voids in the film tends to increase E0 and to decrease x2, f and B while all the above parameters decrease with increasing fraction of amorphous material. In order to support the theoretical conclusions, the experimentally measured properties of the stoichiometric and inhomogeneous films taking into account only microstructure modifications are calculated and compared with the data.