Vibrational Spectra of Vapor-Deposited Binary Borosilicate Glasses

Room temperature infrared absorption spectra in the range 4000–250 cm⁻¹ of binary borosilicate thin glass films deposited by reacting argon‐diluted ${\mathrm{SiH}}_4–{\mathrm{B}}_2{\mathrm{H}}_6–{\mathrm{O}}_2$ mixtures on heated silicon substrates at 300–400°C have been obtained throughout the composition range. Spectra of the end components are found to be in good agreement with those of vitreous SiO₂ and B₂O₃ prepared from the liquid state. The band shapes, intensities, and frequencies of maximum absorption of the $\mathrm{B}–\mathrm{O}$ stretching mode and the $\mathrm{Si}–\mathrm{O}$ stretching mode have been studied as a function of composition. At constant composition the shape of the former band is found to be dependent on the substrate temperature during deposition. Insight into the ``mixing'' nature of these vapor‐deposited glassy solids has been obtained from an analysis of the spectral distribution of $\mathrm{Si}–\mathrm{O}–\mathrm{Si},\mathrm{B}–\mathrm{O}–\mathrm{B},$ and $\mathrm{B}–\mathrm{O}–\mathrm{Si}$ bonds as a function of composition. A new band at 670 cm⁻¹ not previously reported in literature, has tentatively been assigned to a bond bending mode of the $\mathrm{B}–\mathrm{O}–\mathrm{Si}$ centers in the borosilicate structure.