Infrared investigations of hydrogenated amorphous silicon. I. Inductive spectral shifts as predicted from monomer data

Using published i.r. frequencies, a linear correlation is demonstrated for the stretching mode frequencies of all -SiHn (n= 1-3) monomers, when plotted against the Hammett-Taft inductive substituent constant, σ. Extrapolation to a-Si: H (1) supports the presently accepted -SiHn assignments and (2) calls into question the existence of polysilane, (SiH2)n. Extension to other modes for CH3XSiH2 and X2SiH2 monomers, where X = halogen, showed internally consistent σ1 correlations for both series, although series-to-series consistency is lacking: this is demonstrated to arise from questionable peak assignments. Extrapolation of these modes to a-Si:H indicates that peaks are expected in the far-i.r. (<600cm−1), in agreement with recent theoretical and experimental results.