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 h igh resolution electron energy loss spectroscopy and near edge X-ray absorp tion fine structure (NEXAFS:). We observe that at low coverages the adsorpt ion occurs mainly through cycloaddition of the C=C bond to the dangling bon ds of Si-Si dimers, analogous to the behaviour of cyclopentene. The Si-Si d imer bonds are not cleaved in the chemisorption. process as the continued o bservation 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 b ond, confirms the rehybridisation of the carbon atoms in the olefin bond. T he angular dependence of the resonance intensity indicates a molecular plan e inclination of 48 degrees to the substrate plane. At higher dosages, chem isorbed maleic anhydride species are bonded to the Si surface atoms via a s ingle 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 E lsevier Science B.V. All rights reserved.