Abstract: (100) silicon nanowires (SiNW) with different sizes and different surface terminations are studied with first-principles calculation.The results show that the one dimensional band structures of (100) SiNW with H and F terminations are both direct bandgap semiconductors,but SiNWs with an F termination have a smaller band gap and valence effective mass than SiNWs with an H termination.This can be interpreted via the σ-n mixing effect,i.e., the non-bonding 2P electrons (n) of F atoms produce an important orbital mixing with the σ valence electrons.We also predict from the calculations that the extreme of (100) SiNW-a 2×2 helical Si atom chain- is an indirect bandgap semiconductor.This prediction is explained at the end of this paper.

Key words: SiNW, surface termination, fluorinate, band structure, σ-n mixing