Hydrogen adsorption on Ge(100) studied by high-resolution energy-loss spectroscopy

We have studied the adsorption of hydrogen at room temperature and liquid-nitrogen temperature on a Ge(100) single crystal. As in the Si case, two temperature-dependent phases are observed: The monohydride and dihydride phases which show a (2×{}1) and (1×{}1) low-energy electron diffraction (LEED) pattern, respectively. The monohydride-phase saturation is observed at about 500 L (1 L{≡}10^-6 Torr?c) of hydrogen exposure at room temperature; after that value the 105-meV loss, typical of the dihydride-phase presence, appears but the full (1×{}1) LEED pattern is obtained only after about 4000-L exposure. The width of the specularly reflected elastic peak grows with increasing hydrogen exposure up to a maximum value at 500 L, indicating that the monohydride phase on Ge(100) has a lower surface resistivity with respect to clean or dihydride-covered Ge. Hydrogen exposure at 100 K shows a new peak at 195 meV which is not completely due to water contamination; the origin of this peak is not clear at present.