Variable energy x-ray photoemission studies of alkylsilane based monolayers on gold

Gaseous n-hexylsilane (C6H13SiH3), n-octylsilane (C8H17SiH3), and n-octadecylsilane (C18H37SiH3) have been vapor deposited in ultrahigh vacuum (UHV) on freshly evaporated gold surfaces to form monolayers. Surface sensitive X-ray photoemission studies utilizing synchrotron radiation in the 160-360 eV range have been used to characterize these systems. Analyses of the C 1s, Si 2p, and Au 4f and valence band regions permit a structural assessment of the monolayer. The full width at half-maximum of the Si 2p and C 1s core levels, 0.4 and 1.2 or 1.1 eV, respectively, suggest the monolayers are chemically homogeneous. The intensity variation of the Au 4f and Si 2p core levels at different photon energies indicate the surface coverage of the monolayer is ∼96% and the chain orientation is upright on the surface, not parallel to the surface. The valence band of the alkylsilane monolayers exhibit features at ∼-13.2, -14.6, -16.3, -17.6, and -18.9 eV that agree well with those observed for alkyl chains of the same length.