INTERACTION OF OXYGEN WITH ALKALI-METALS AT THE GE(001) SURFACE STUDIED BY METASTABLE DEEXCITATION SPECTROSCOPY

The local electronic structures of oxygen plus alkali-metal (Cs) coads orption layers on Ge(001) surfaces have been studied by metastable dee xcitation spectroscopy (MDS). Upon admission of oxygen to a Cs-saturat ed Ge(001) surface, the emission intensity in MDS due to the Cs 6s sta tes (<6(s)over tilde>) rapidly decreased, indicating direct transfer o f (s) over tilde electrons to oxygen. This charge transfer, however, r emained incomplete even with heavier exposures of oxygen. When O/Cs/Ge surfaces were thermally annealed at about 700 K, oxygen atoms adsorbe d at Cs-bonded sites were transferred to Ge-bonded sites, producing Ge -O compounds. The compounds were desorbed when annealed at temperature s above 800 K. The results show a fairly different behavior of oxygen at alkalated Ge(001) surfaces compared to that at alkalated Si(001) su rfaces.