Evidence for anomalous structural relaxation in SiO2 films

Evidence from both thermal oxide films and bulk samples is discussed for whether amorphous SiO2 exhibits the anomalous property that the annealing of volume or refractive index may become more rapid at high densities solely due to structural effects. Unlike typical glasses, volume changes in SiO2 are not governed by free volume but by reorientations of SiO4 tetrahedra. This may be reflected in the larger initial volume changes found in the annealing of bulk SiO2 corresponding to higher initial densities at the same temperature. It is also suggested by an apparent reverse asymmetry between volume expansion and volume contraction which appears to be unique to SiO2 but not previously noted. These features are incorporated into a self-consistent annealing model for an analysis of the Landsberger–Tiller annealing data for thermally grown SiO2 films which is based on structural relaxation and which is compatible with high temperature data.