Thermal dehydrogenation of polysilane

Abstract

The isochronal thermal decomposition of polysilane, -(SiH₂) _n- , has been investigated at temperatures up to 335°C by in situ infrared spectroscopy. The studies were performed, in vacuo, on compressed discs of polysilane in a KBr matrix. Dehydrogenation was measured by the reduction of the infrared stretching ωs(2100 cm⁻¹), bending ω_b(910 cm⁻¹), wagging ω_w(865 cm⁻¹) and rocking ω_r(650 cm⁻¹) integrated band intensities. The wavenumbers of the infrared-active modes of -(SiH₂) _n - given in parenthesis correspond to room temperature samples. Loss of hydrogen occurs at relatively low temperatures, ca. 140–200°C, and is essentially complete at 335°C. The integrated intensities of each band show an equal decrease with time. However, the peak position of the essentially degenerate symmetric and asymmetric stretching mode shifted systematically to lower wave-numbers in the region 2100 cm⁻¹-2080 cm⁻¹ on dehydrogenation. No shift was effected in the doublet of peaks in the range 800–950 cm⁻¹ under the same conditions. The width (f.w.h.m.) of the 650 cm⁻¹ band decreased with a reduction in the hydrogen content. This band exhibited a slight red shift of 10 cm⁻¹ on dehydrogenation. Preliminary studies of the oxidized polysilane films demonstrated that rearrangement of [SiH₂O] groupings to [SiH₂O₂] groupings takes place at elevated temperatures.