Variable Energy X-ray Photoemission Studies of Alkylsilane Based Monolayers on Gold

Abstract

Gaseous n-hexylsilane (C 6 H 13 SiH 3 ), n-octylsilane (C 8 H 17 SiH 3 ), and n-octadecylsilane (C 18 H 37 SiH 3 ) 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.

Hydridosilane Modification of Metals: An Exploratory Study

“…In studies of trihydridosilane interaction with gold, Owens et al [8] noted the absence of hydrogen bound to silicon on silane treated gold substrates and likened it to the absence of hydrogen bound to sulfur for the alkylthiol treated gold substrates. The observation that a trihydridosilane (three hydrogens bound to silicon) would have similar behavior to an alkylthiol (one hydrogen bound to sulfur) initially appeared to be consistent with our observations.…”

“…Upon further consideration, this appeared to be inconsistent with the observation that the monohydridosilanes, with one hydrogen bound to silicon and therefore more similar to the alkylthiols, did not perform as effectively for modifying substrates. Tunneling AFM (TAFM) of alkylsilanes on metal substrates would be anticipated to provide the most direct information, but as noted by Owens et al [8], the observation of self-assembled monolayers (SAMs) on metal substrates by TAFM is difficult due to tunneling current requirements [9]. In studies concerning the synthesis of Pd nanoparticles in the presence of trihydridosilanes, Chauhan et al similarly failed to observe silyl hydride absorption bands in infrared studies [10].…”

A spectroscopic study of self-assembled monolayer of porphyrin-functionalized oligo(phenyleneethynylene)s on gold: the influence of the anchor moiety

“…In recent studies of the alkylsilane (C n H 2nÀ1 SiH 3 ) SAMs on Au, the Si 2p 3/2,1/2 peak was observed at a BE of 99.8 eV and with fwhm of 0.4 eV. 71,72 It was proposed that three Si-H bonds are cleaved during the SAM formation, and then Si atoms form three covalent bonds to the gold surface. 71,72 In the case of the TMS-ethynyl system of this study, the observed BE position of the Si 2p peak (101.9 eV) is higher, which indicates that not all Si-CH 3 bonds are cleaved upon the film formation.…”

Monolayer Pattern Evolution via Substrate Strain-Mediated Spinodal Decomposition

“…Afterwards, adsorption dynamics slow dramatically with saturation coverage reached at 300 L exposure. Comparison with alkanethiol adsorption indicates 95 5% monolayer surface coverage [9]. Here, scanning tunneling microscopy (STM) is employed to investigate pattern formation dynamics of the n-octylsilane (C 8 H 17 SiH 3 ) monolayer.…”