The adsorption and thermal decomposition of H2O and H 2S on Ge(100 were studied with temperatureprogrammed desorption (TPD and X-ray photoelectron spectra (XPS, using synchrotron radiation. At 105 K, H2O molecules either adsorb molecularly or dissociate to form surface OH and H for exposures of all durations. Chemisorbed H2O dissociates to form surface OH on annealing to 270 K, whereas H2S dissociates to form surface SH and H on an initial exposure and further adsorbs molecularly on protracted exposure to the surface at 105 K. The calculation with density-functional theory (DFT shows that H2S undergoes dissociative adsorption with a negligible barrier (2.1 kJ/mol but H2O dissociates with a larger barrier (26.8 kJ/mol. On annealing to 550 K, surface OH mainly recombines with surface H to evolve H2O, but a small proportion of surface OH decomposes to form surface O and H. Most surface SH undergoes decomposition to form surface S and H at 520 K. According to a DFT calculation, surface OH has an activation energy for decomposition greater than that for recombination with surface H, whereas activation energies for decomposition and recombination of surface SH show the reverse order. Surface H resulting from the dissociation of H2O and H2S is thermally activated to combine and to desorb as H2 at 620 K. For H2S, a small proportion of surface H recombines with surface S to desorb as H2S. Finally, surface O and S are removable from the surface with desorption of GeO at 710 K and GeS at 695 K, respectively.
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