Reactivity towards O2 and H2O of the alkali-metal induced Ge(1 1 1)-3 × 1 surfaces: contrasting adsorption rates for different alkali metals

Using photoemission and Auger-electron spectroscopies, we investigated the reactivity towards oxygen and water of the alkali-metal induced Ge(1 1 1)-3 × 1 surface at room temperature. The adsorption of both gases on the Ge(1 1 1)-3 × 1 surfaces induced by Na and K are significantly suppressed, but greatly enhanced on the Li-induced Ge(1 1 1)-3 × 1 surface. This difference in the surface reactivity of the alkali-metal induced Ge(1 1 1)-3 × 1 surfaces contrasts not only to the expectation of the similar reactivity inferred from the common 3 × 1 reconstruction structure, but to the trends in the elemental alkali metals. It is proposed that the competition of the dangling-bond saturation and the AM-mediated oxidation determine the surface reactivity of the Ge(1 1 1)-3 × 1 surfaces.