Infrared Band Assignments in Oxidised Hydrogenated a‐Si Films

The infrared transmission spectra of two ‘polysilanes’ of approximate composition (SiH₂)_x and (SiH)_x, prepared by chemical means, have been measured in the range 4000 to 650 cm⁻¹. The appearance of new bands in the infrared spectra during the oxidation of films of these materials by exposure to air is interpreted in terms of changes in the local environment around the silicon‐hydrogen moieties. It is demonstrated that the wave number of the silicon—hydrogen stretching modes of SiH and SiH₂, groups vary systematically with the number and electronegativity of the next neighbouring atom. The influence of the inductive effect on the stretching frequencies can be empirically related, following the methodology of Lucovsky, to the Pauling electronegativity sum of the adjacently bound oxygen atoms. The infrared band frequencies exhibited in the oxygenated ‘polysilane’ samples correspond exactly with bands that arise during the exposure of certain undoped and P‐doped hydrogenated a‐Si films to air. Ageing phenomena produced in r.f. discharge a‐Si films are associated with the porosity and oxidation of a hydrogen rich phase in the amorphous material.