Chemical Passivation of Silicon Nanowires with C₁−C₆ Alkyl Chains through Covalent Si−C Bonds

We report on the functionalization of Si NWs with C 1 −C 6 alkyl chains using a versatile two step chlorination/alkylation process. We show that Si NWs terminated with C 1 −C 6 molecules, through Si−C bonds, connect alkyl molecules to 50−100% of the Si atop sites and provide surface stability that depends on the chain length and molecular coverage, according to the following order: C 1 −Si NW > C 2 −Si NW > (C 3 −C 6 )−Si NW. Our results indicate that the oxidation resistance of (C 1 −C 2 )−Si NWs is significantly higher than equivalent 2D Si(100) surfaces, whereas (C 3 −C 6 )−Si NWs are comparable to 2D (C 3 −C 6 )−Si(100). These discrepancies can be explained as follows: the lower the molecular coverage, the higher the probability for interaction between oxidizing agents (O 2 or H 2 O) and molecule-free sites. Our results are of practical importance when reduced amounts of oxide are required, e.g., for radial epitaxy on NWs to realize vertical P−N junctions for solar cells or for radial Si/Ge superlattices for application in optoelectronics.