Determination of the bonding of alkyl monolayers to the Si(111) surface using chemical-shift, scanned-energy photoelectron diffraction

The bonding of alkyl monolayers to Si(111) surfaces has been studied by conventional x-ray photoelectron spectroscopy (XPS) and chemical-shift, scanned-energy photoelectron diffraction (FED) using synchrotron radiation. Two very different wet-chemical methods have been used to prepare the alkyl monolayers: (i) olefin insertion into the H-Si bond on the H-Si(111) surface, and (ii) replacement of Cl on the Cl-Si(111) surface by an allyl group from an alkyllithium reagent. In both cases, XPS has revealed a C 1s signal chemically shifted to lower binding energy, which we have assigned to carbon bonded to silicon. PED has shown that both preparative methods result in carbon bonded in an atop site with the expected C-Si bond length of 1.85+/-0.05 Angstrom. Chemical-shift, scanned-energy photoelectron diffraction is a particularly valuable probe of local structure at surfaces that contain the same element in multiple, chemically distinct environments. (C) 1997 American Institute of Physics.