High-resolution photoemission study of acetylene adsorption and reaction with the Si(100)-2x1 surface

The adsorption and reaction of acetylene with the Si(100)-2X1 surface has been studied using high-resolution photoemission by monitoring the Si 2p, C 1s, and valence-band (VB) spectra as a function of both acetylene coverage and post-adsorption annealing temperature. After the clean Si(100) surface is exposed to 0.5 monolayer (ML) acetylene, the surface state in the VB is absent. Meanwhile, the curve-fitting results show that there is only one interface component in the Si 2p core level. These results indicate that the asymmetric Si dimers may become symmetric dimers after acetylene adsorption, which can be explained well by the tetra-sigma model determined from our previous photoelectron holographic results. Significant changes in the electronic structure (Si 2p, C 1s, and VB) are found after subsequent annealing of the saturation overlayer, Annealing at lower temperature can induce some acetylene molecule desorption while most of the molecules decompose into C2Hx (x= 1,0) and H species. After annealing above 660 degrees C, both of the reacted components of the Si 2p and C Is lines show that the SiC species form clustertike features. At the same time, the VB and Si 2p spectra indicate a restoration of a Si(100)-2X1 structure, and the asymmetric Si dimers reappear on the surface. [S0163-1829(99)02040-8].