WATER-VAPOR ADSORPTION ON THE SI(111)-(7X7) SURFACE

Clean Si(111)-(7 x 7) reconstructed surfaces have been exposed to incr easing doses of H2O up to 15000 L at room temperature. At each stage t he surface was studied by electron energy-loss spectroscopy (EELS), Au ger electron spectrometry (AES), photoemission yield spectroscopy (Pk' S) and low-energy electron diffraction (LEED). The dissociative adsorp tion of H and OH onto the Si(111)(7 x 7) surface dangling bonds, and t he formation of Si-O-Si bonds are revealed through the changes in stru ctural compositional and electrical properties. At water doses lower t han 150 L, the (7 x 7) pattern is not affected by the reaction. The da ngling-bond saturation by H and OH is dominant, but the formation of S i-O-Si bonding is significant. At higher doses, the former dangling bo nds become mostly H-saturated, and the oxygen uptake consists mainly o f the formation of Si-O-Si bonds through a process in which the surfac e becomes fully disordered.