Covalent Attachment of Acetylene and Methylacetylene Functionality to Si(111) Surfaces: Scaffolds for Organic Surface Functionalization while Retaining Si−C Passivation of Si(111) Surface Sites

Si(111) surfaces have been functionalized with Si−CC−R species, where R = H or −CH₃, using a two-step reaction sequence involving chlorination of H−Si(111) followed by treatment with Na−CC−H or CH₃−CC−Na reagents. The resulting surfaces showed no detectable oxidation as evidenced by X-ray photoelectron spectroscopic (XPS) data in the Si 2p region, electrochemical measurements of Si−H oxidation, or infrared spectroscopy. The Si−CC−R-terminated surfaces exhibited a characteristic CC stretch in the infrared at 2179 cm^-1, which was strongly polarized perpendicular to the Si(111) surface plane. XPS measurements in the C 1s region showed a low binding energy peak indicative of Si−C bonding, with a coverage that was, within experimental error, identical to that of the CH₃-terminated Si(111) surface, which has been shown to fully terminate the Si atop sites on an unreconstructed Si(111) surface. The Si−CC−H-terminated surfaces were further functionalized by exposure to n-C₄H₉Li followed by exposure to para Br−C₆H₅−CF₃, allowing for introduction of para −C₆H₅CF₃ groups while maintaining the desirable chemical and electrical properties that accompany complete Si−C termination of the atop sites on the Si(111) surface.