Adsorption of maleic anhydride on Si(100)-2 x 1

The adsorption of maleic anhydride on Si(100)-2 x 1 has been studied with high resolution electron energy loss spectroscopy and near edge X-ray absorption fine structure (NEXAFS:). We observe that at low coverages the adsorption occurs mainly through cycloaddition of the C=C bond to the dangling bonds of Si-Si dimers, analogous to the behaviour of cyclopentene. The Si-Si dimer bonds are not cleaved in the chemisorption. process as the continued observation of a 2 x I pattern in low energy electron diffraction shows. In the NEXAFS spectra, the absence of a rr resonance associated with the C=C bond, confirms the rehybridisation of the carbon atoms in the olefin bond. The angular dependence of the resonance intensity indicates a molecular plane inclination of 48 degrees to the substrate plane. At higher dosages, chemisorbed maleic anhydride species are bonded to the Si surface atoms via a single Si-C linkage with retention of the C=C double bond. In this case. the dissociated hydrogen bonds to one of the neighbouring Si atoms. (C) 2001 Elsevier Science B.V. All rights reserved.