A METASTABLE DEEXCITATION SPECTROSCOPY STUDY ON THE OXYGENATION OF ALKALATED GE(001) SURFACES

The local electronic structures of both Cs-adsorbed and Cs + oxygen-co adsorbed layers on Ge(001) surfaces have been studied by metastable de -excitation spectroscopy (MDS). Cs 6s-induced states (<6(s)over tilde> ) developed just below E(F) with increasing Cs coverage, but the redis tribution of electrons in these states to induce polarization or ioniz ation at adsorbed Cs was weaker than that at Si surfaces. Electrons ra pidly flowed out from the Cs <6(s)over tilde> states when the Cs adlay er was exposed to oxygen. The oxygenation process consisted of initial fast and second slow steps, the break point between which occurred at a dosage of 0.1 oxygen atoms per (2 x 1) unit cell. Electron transfer from Cs <6(s)over tilde> to oxygen remained incomplete, even at the s econd step. Possible origins of the difference between the O/Cs/Ge and the O/Cs/Si systems in the role played by adsorbed Cs in the oxygenat ion process are discussed.