Electronic properties of methyl and hydrogen terminated Si(111) surfaces

Functionalized Si(111) surfaces have many applications in photo-electrochemistry, and some of those (e.g. the use of Si rods as photo-cathodes in solar cell applications) require the development of chemical protection strategies so as to prevent uncontrolled oxidation. Recently [1] a full methylation of Si(111) has been achieved experimentally, which constiutes a promising means to protect Si(111) from oxidation. However, the apparently simple atomic structure of this surface is still under debate. In particular, low temperature STM images appear to yield a pattern in disagreement with structural, first principles optimizations. We have carried out a series of ab-initio calculations of both the structural and electronic properties of the CH3-Si(111) aimed at interpreting STM and STS measurements. A comparison between results obtained at the DFT-GGA level and by using GW calculations will be presented and compared with the corresponding ones for the H-Si(111). This work supported by grant NSF-CHE-0802907 [1]H. Yu et al., Appl. Phys. Lett. 88, 152111, (2006)