TEMPERATURE-ACTIVATED REACTIONS OFH2OANDNH3WITH H-PASSIVATED Si(111) SURFACES

Chemically hydrogenated surfaces Si(111)(1×1)–H were exposed sequentially, at temperatures of up to 600°C, and to low pressures ofH2OorNH3. The interaction processes have been studied by low energy electron diffraction and by photoemission yield and Auger electron spectrometries. The temperature threshold forH2Oreaction is 350°C, at which, in a first stage, OH dipoles replace adsorbed H. OH dipole density is limited below 1/3 monolayer by the Si–O–Si formation, which brings disorder and restores H passivation. ForNH3, the reaction threshold is 370°C, at which only a small density ofNH2dipoles is stabilized at saturation. Beyond 370°C, the saturatedNH3/Si(111)–H reaction is characterised by an increasing substitution ofNH2dipoles to H atoms. At higher temperatures, the loss of hydrogen leads to surface disorder, which induces a loss of the N-related dipole moment normal to the surface.