ADSORPTION OF ACETYLENE ON THE SI(100)-(2X1) SURFACE

The adsorption of acetylene on the Si(100)-(2 X 1) surface has been studied by high-resolution electron energy-loss spectroscopy (HREELS) and temperature programmed desorption. An energy loss peak at 1450 cm-1, which can be assigned to a C=C double bond, is observed unambiguously in the HREEL spectra. This observation provides direct evidence for the sp2 di-sigma adsorption model. The unusually low frequency for the C=C vibration is most likely due to an interaction between the Si atoms and the rehybridized acetylene pi orbital. As the surface temperature is increased, one of the C-H bonds cleaves to form a monohydride (Si-H). Most of the acetylene dissociates over a wide temperature range to produce surface carbon and hydrogen. The carbon atoms remain on the surface to form silicon carbide (SiC), while the hydrogen atoms recombine to form molecular hydrogen, which desorbs from the Si(100) surface.