Vibrational Spectra and Structure of Silica Gel Films Spun on C-Si Substrates,

A series of silica gel films were spin-coated on single crystal silicon c-Si substrates and their structure was characterized by vibrational spectroscopy. The films were either dried at room temperature or partially densified at 450 0 C. Fourier transform infrared absorption spectra have been obtained for each film and they are compared to the spectrum of thermal SiO2 films. The gel films ca. 150 nm thick show the presence of residual OH groups, but very little molecular water or organic species and the fundamental Si-O-Si vibrations exhibit shifts toward lower frequencies, compared to the thermal oxide. The Si-O-Si antisymmetric stretch near 1070 cm -1 was narrower for the gels and the shoulder on the high frequency side was stronger. The nature of this feature is discussed based also on oblique incidence transmission and reflection-absorption spectra taken with polarized infrared light.