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

We report on the functionalization of Si NWs with C1-C6 alkyl chains using a versatile two step chlorination/alkylation process. We show that Si NWs terminated with C1-C6 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: C1-Si NW > C2-Si NW > (C3-C6)-Si NW. Our results indicate that the oxidation resistance of (C1-C2)-Si NWs is significantly higher than equivalent 2D Si(100) surfaces, whereas (C3-C6)-Si NWs are comparable to 2D (C3-C6)-Si(100). These discrepancies can be explained as follows: the lower the molecular coverage, the higher the probability for interaction between oxidizing agents (O2 or H2O) 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.