CHEMISORPTION OF H, H2O AND C2H4 ON SI(113) - IMPLICATIONS FOR THE STRUCTURE

The chemisorption of H, H2O and C2H4 on Si(113) is studied by means of high-resolution electron energy loss spectroscopy (HREELS) and low-energy electron diffraction (LEED). By saturating the dangling bonds of the clean Si(113)3 x 2 surface, H forms a monohydride first. At higher exposures a dihydride phase is formed, clearly distinguishable in HREELS through the appearance of the H-Si-H scissor mode. H2O dissociates into H and OH. Its sticking coefficient is of the order of one, indicating that Si dimers may constitute the Si(113)3 x 2 sur-face to a large part. H, OH and C transfer the surface structure from 3 x 2 into 3 x 1 adsorbate. At least in the case of H chemisorption the change of structure occurs very likely without lateral Si transport. This has strong implications for the structure of the clean Si(113)3 x 2 surface. To account for these findings together with our photoemission results and two scanning tunneling microscopy (STM) studies from the literature we propose a buckling model for the Si(113)3 x 2 surface. Our investigation underlines that only the absence of H, OH and C - the main residues from contamination through background gas - guarantees the occurrence of the 3 x 2 reconstruction for the clean Si(113) surface.