Time Dependence of Optical Properties of Vacuum-Evaporated Poly(di-methyl silane) Thin Films

In this paper, we show an interesting change in the optical properties of poly(di-methyl silane) thin films prepared by vacuum evaporation. We have found that the strength of the optical absorption peak at ~300 nm is changed depending on the substrate temperature during the deposition. The strength of the optical absorption peak at ~300 nm decreases with increasing time when the thin film is prepared at a high substrate temperature. On the other hand, the peak does not appear when the thin film is prepared at a low substrate temperature. However, in the latter case, the optical absorption peak appears at ~300 nm with time. Moreover, the change of the optical absorption strength of the specimen held in a vacuum desiccator is different from that of the specimen held in atmosphere. It is considered that the decrease of the optical absorption strength at ~300 nm is due to the decrease of the molecular weight of polysilanes, and the increase is due to the structural relaxation of polysilane chains.