Abstract

Instability of refractive index in thin films is attributed to adsorption and desorption of water in the porous columnar structure present. Electron beam evaporated zirconia films are particularly susceptible to this problem because void fractions in these films can exceed 40 %. One approach to reducing the void fraction in zirconia films is ion-assisted deposition. In this work we show a decrease in void fraction in coevaporated zirconia:silica films. In addition, films containing ~20% silica by volume show higher refractive indices than pure zirconia films. The films were produced by coevaporation from independent electron/beam sources onto fused silica substrates at 300°C. Each source was monitored independently by a quartz-crystal monitor. The thicknesses and refractive indices of the films were computed from stylus surface profiling, channel spectra, and m-line spectroscopy. A densification factor, computed from the ratio of the sum of the individually monitored thicknesses to the measured film thickness, was greater than unity for all mixed films. A simple model suggests that the void fraction of the pure zirconia films is 25–40% and decreases with increasing fraction of silica.

© 1985 Optical Society of America