Dissociative adsorption and thermal evolution of carbon tetrachloride on Si(111)7 x 7

The adsorption of CCl4 on Si(111)7 x 7 at room temperature has been characterized by electronic and vibrational electron energy loss spectroscopy (EELS). CCl4 was found to adsorb dissociatively on Si(111)7 x 7 with the formation of Si-Cl bond and adsorbed CClx species. At high exposures, CCl4 appears to more readily undergo a greater degree of dechlorination. Using a Si16H18 cluster to model only the adatom-restatom site, our density functional theory calculations suggest two plausible adstructures involving the dissociated Cl and CCl3 fragments. The wavenumbers of the observed EELS features are found to be in general accord with the corresponding calculated wavenumbers. Thermal evolution of the adsorbed fragments has been followed by both vibrational and electronic EELS as a function of the sample annealing temperature. A new EELS feature at 920-960 cm(-1) attributed to SiC film or alloy formation is found to emerge at 573 K, while the Si-Cl stretch at 550 cm-1, corresponding to dissociated Surface Cl, is removed upon annealing to similar to 883 K. Furthermore, the electronic EELS spectra reveal an energy loss at 9.3 eV that can be assigned to a single-electron transition from the Cl(p(z)) bonding state to the Cl(p(z)) antibonding state produced by the Si-Cl bond. (C) 2008 Elsevier B.V. All rights reserved.