Electronic Structure of Poly(dimethylsilane) and Polysilane Studied by XPS, UPS, and Band Calculation

Abstract
The valence electronic structures of poly(dimethylsilane)(PDMS) (Si(CH3)2)n and polysilane (SiH2)n were studied. PDMS was experimentally studied by X-ray photoelectron spectroscopy (XPS) and UV photoelectron spectroscopy (UPS), and band calculations were performed for both compounds. The observed spectral features and calculated band structures were assigned and discussed through a comparison with theoretical and experimental results for oligomers and other polymers. These analyses have demonstrated how the electronic structures of these compounds are correlated through factors such as (i) change in the chain length, (ii) methylation, and (iii) the substitution of Si by C. PDMS has a small ionization energy (5.9 eV) almost as low as that of poly(p-phenylene) (5.6 eV). This small value comes from the combined contribution from the small electronegativity of silicon, σ-conjugation, and the inductive effect of methyl groups. The small ionization energy and large σ-conjugation explain the reported high conductivity of PDMS and its derivatives upon acceptor doping.