Two kinds of low pressure CVD SiO2samples, heterogeneous film and homogeneous “snow,” have been collected on stainless steel substrates at three different deposition temperatures: 523, 643, and 703 K. They have been characterized thermodynamically by transposed temperature drop and high temperature solution calorimetry. Both film and “snow” samples are metastable—in terms of enthalpy relative to bulk Si02glass—by up to 101 kJ-mol1. The excess enthalpy increases with decreasing deposition temperature and is larger for “snows” than for films. On annealing at high temperatures, it gradually disappears. IR and Raman spectroscopies indicate that both Si-H and Si-OH species are present in the as-deposited samples but disappear upon annealing. All as-deposited samples have densities comparable to bulk Si02glass, ie. between 2.0 and 2.2 g-cm-3. Annealing tends to increase the density of all samples.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry