Crystallinity polysilylenes

The effect of main chain crystallization was not studied because of our inability to prepare coherent thin films of highly crystalline polysilylenes such as polydimethylsilylene or polydiethylsilylene. 

Crystalline silicon is the most widely used semiconductor material today, with a maiket share of above 90%. Because of its indirect electronic band structure, however, the material is not able to emit light effectively and therefore carmot be used for key applications like light-emitting diodes or lasers. Selected one- or two-dimensional silicon compounds like linear or branched polysilylenes [1] or layered structures like siloxene [2], however, possess a direct band gap and therefore exhibit intense visible photoluminescence. Siloxene, a solid-state polymer with a sheet-like layered structure and an empirical formula Si H (OH) , in particular, is considered as an alternative material for Si-based liuninescent devices. Detailed studies of stmctural and photophysical properties of the material, however, are strraigly impeded by its insolubility in organic solvents. 

In all of the polysilylenes studied, the fluorescence from neat thin films on fused silica substrates exhibits a blue shift upon cooling. In cases where our studies have spanned the glass transition of the polymer, no change in behavior is seen (Figure 4). In the polymers which have substantial crystallinity, an abrupt shift in behavior occurs at the crystalline melting point above this temperature the films behave in much the same fashion as the fluid solutions. These phenomena have been extensively studied (9,12,13) and will not be treated here. 

---