Desities of Amorphous Thin Films

The densities of amorphous Ge, C, SiO, Se, and WO3 films prepared by vacuum-evaporation were measured using multiple beam interferometry in combination with an oscillating crystal microbalance. Optically polished quartz crystals were used as both the microbalance sensing elements and the substrates for interferometry. The film densities were found to be independent of thickness. The measurements indicated that the amorphous film densities were 23–31% less than the crystalline bulk densities and 13–14% less than the amorphous or vitreous bulk densities. This density decrease may be attributed to voids, the presence of which is deduced from a microcrystalline model of the amorphous structure confirmed by recent high-resolution electron microscopic observation.