LAYERED POLYSILANE - THERMOLYSIS AND PHOTOLUMINESCENCE

Layered polysilane (Si6H6) and its thermolysis have been studied using FTIR spectroscopy, thermogravimetry/differential thermal analysis, ma ss spectrometry, electron paramagnetic resonance, Si K-edge absorption and photoluminescence spectroscopy. It is found that cross-linking be tween (-Si6H6-)(n) layers occurs through dehydrocoupling reactions whe n the layered polysilane is heated under vacuum or an inert atmosphere at temperatures of 100-200 degrees C. Structural changes in the silic on network are evident during thermolysis: the layered structure of po lysilane starts to collapse at 200 degrees C and is transformed to amo rphous hydrogenated silicon and subsequently to crystalline silicon (c -Si) at temperatures higher than 450 degrees C. This process is accomp anied by the evolution of H-2 and SiH4 gases. The resulting layered po lysilane exhibits strong room temperature photoluminescence at 560 nm (ca. 2.2 eV) and a blue-shift of Si K-edge absorption (0.6 eV) relativ e to c-Si. Annealing the layered polysilane results in red-shifts of l uminescence peak energy with the increase of annealing temperature, co nsistent with the trend observed in the Si K-edge absorption measureme nt. These results are interpreted in terms of the growth of silicon ne twork dimension during the thermolysis. The reduction in visible lumin escence intensity for the annealed product at 300 degrees C (or higher ) is further attributed to the creation of defects, e.g., silicon dang ling bonds (g = 2.0047) which provide pathways for non-radiative recom bination. The relationship between layered polysilane (as well as its annealed products) and porous Si is discussed.