Thermal decomposition of C₂N₂ on Si(100)-2x1 and Si(11)-7x7

The adsorption and thermal decomposition of C₂N₂ on Si(100)-2x1 have been investigated with TPD, XPS, UPS, and HREELS. For the C₂N₂ species, two desorption peaks at 160 and ∼230 K were noted in the TPD spectrum, deriving from the C₂N₂ adsorbed in overlayers and the submonolayer, respectively. The latter showed C_1s and N_1s XPS peaks at ∼1.8 eV lower in binding energy than those of the multilayer C₂N₂. The large energy shift in the XPS peaks is likely caused by the strong interaction between the C₂N₂ adsorbed side-on and the surface at lower coverages. Annealing the C₂N₂-doses Si(100) at ∼600 K caused the breaking of the NC-CN bond, and the CN adspecies could be identified on the surface. At 700-800 K, CN bond scission occurred, and thus a mixture of silicon carbide and silicon nitride was formed. Similar results were found for C₂N₂ on Si(111)-7x7; however, the relative signal intensities, e.g., C_1s and N_1s XPS and HREELS, are weaker than those of the C₂N₂ on Si(100). This difference may be attributable to the fact that there are fewer dangling bonds on Si(111)-7x7 than on Si(100)-2x1.