Chemisorption ofH2O onGexSil−x(100)(2×1)

The chemisorption of ${\mathrm{H}}_2$O on the (100) surface of clean, ordered Ge-Si alloys has been investigated using high-resolution electron-energy-loss spectroscopy. It was found that ${\mathrm{H}}_2$O chemisorbs dissociatively producing surface hydride and surface hydroxide species as is seen for ${\mathrm{H}}_2$O on Si(100)(2×1) surfaces. For the ${\mathrm{Ge}}_{\mathrm{x}}$ ${\mathrm{Si}}_{1\mathrm{-}\mathrm{x}}$(100)(2×1) substrates, a (2×1) pattern is observed after saturation with ${\mathrm{H}}_2$O indicating that the dimer structure of the substrate is preserved. Both Ge-H and Si-H stretching modes are observed though the former is more intense at room temperature even for x as low as 0.2 because of surface segregation during the cleaning procedure. If, however, the sample is heated after chemisorbing ${\mathrm{H}}_2$O, there is a gradual inversion of the surface semiconductor-atom concentration presumably attributable to the greater relative reactivity of Si.