Soft X-ray fluorescence spectra of photoluminescent layered polysilanes

The electronic structures of layered polysilanes (Si6nH6) derived from the cross-linking of planar (Si6H6) sheets via the elimination of the interplane H atoms are investigated with full-potential LAPW calculations. The electronic band gap energy of the polysilanes is found to be red-shifted with increasing number of stacking sheets and approaches the bulk Si value. The calculated soft X-ray fluorescence difference spectra of polysilanes and bulk Si show features in strong resemblance to those observed in the difference spectrum between porous-silicon and bulk Si. This observation suggests that the nanostructure in the porous Si obtained from the electrochemical etching of an n-Si[100] wafer may exist in a form akin to thin Si6H6 sheets.