Novel method for functionalizing Si(111) surfaces with inorganic complexes

Functionalization of silicon semiconductor surfaces with mol. catalysts is of interest for the generation of solar fuels. There are several methods of attaching these catalysts to the Si(111) surface through covalent bonds. The first is hydrosilylation, where terminal olefins are reacted with a hydrogen-terminated surface to form the Si-C bond. Another route employs a "two-step" chlorination/alkylation procedure whereby a hydrogen-terminated Si surface is chlorinated and then reacted with an alkyl Grignard reagent to form the Si-C bond. The hydrosilylation method is fast and leads to high coverage of groups with varied functionalities, but often results in incomplete surface functionalization and high surface oxidn. The "two-step" chlorination /alkylation method can be used to form monolayers of very high surface coverage, but the method is not applicable to groups contg. other reactive moieties Here, we report a new method of functionalizing Si(111) surfaces by combining these two procedures. We detd. the conditions under which a hydrosilylation-like reaction could be performed on a chlorine-terminated Si surface to attach larger, varied functional groups to the surface, followed by a methylation reaction to fill in the unreacted surface sites. These surfaces have been characterized using XPS and photocond. decay measurements to det. surface coverage and carrier lifetimes. These studies indicate that the surface coverage of various functional groups, including vinylferrocene and fluorostyrene, can be varied controllably from 0 up to 60%. These mixed monolayers have surface recombination velocities (SRVs) that are similar to those measured on methyl-terminated surfaces. The vinylferrocene functionalized surfaces have been used in photoelectrochem. studies, showing fast electron transfer kinetics to the ferrocene group, with rate consts. on the order of 100 s^(-1)