Adsorption of maleic anhydride on Si(1 0 0)-2×1

The adsorption of maleic anhydride on Si(1 0 0)-2×1 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 2×1 pattern in low energy electron diffraction shows. In the NEXAFS spectra, the absence of a π* 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° 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.