OPTICAL-PROPERTIES OF COBALT OXIDE-FILMS DEPOSITED BY SPRAY-PYROLYSIS

The optical constants of Co3O4 films were determined by analyzing vari able angle of incidence spectroscopic ellipsometry data and normal inc idence transmittance data, between 3500 and 17 000 Angstrom. Absorptio n was taken to be nonzero for the soda-lime-silica float glass substra te. The absorption of the soda-lime-silica float glass was fitted by a n ensemble of four Gaussian oscillators over the entire measured spect ral range. Surface roughness of the film was measured with atomic forc e microscopy and included in the optical model. The films were deposit ed by spray pyrolysis of cobalt acetylacetonate onto heated soda-lime- silica float glass and fused silica substrates. Fused silica was used to observe film absorption without the effect of substrate absorption. The oxide film phase was identified with thin-film x-ray diffraction analysis. Simultaneous fits of ellipsometry and transmittance data fro m coated samples were computed to obtain the film thickness, optical c onstants, and the amplitudes of the four Gaussian oscillators represen ting the glass substrate absorption. This analysis was done by treatin g the optical constants at each wavelength as simple fitting parameter s or as variables with a Kramers-Kronig consistent parametric model. S pectra for the most accurate optical constants of Co3O4 films deposite d by spray pyrolysis onto both substrates are presented. (C) 1996 Amer ican Vacuum Society.