Electron spectroscopy using spin-selected metastable atoms

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Metastable atom electron spewctroscopy is based on an analysis of electrons emitted by thermal collisions between rare-gas metastable atoms and solid surface. Since metastable atoms such as He^<**>(1s2s, 2^3S) can not penetrate into the bulk, the localionization takes place at the outermost surface layr. Further, the electron emission occurs through electron transfer from the metastable atom to solid surface, hence the transition rate is governed essentially by the spatial distribution of wave-function of the surface. Using these features, we have applied this method to probe the electronic structure of transition-metal oxides, in which the electron correlation effects plays an important role.The electron emission spectrum of LaCoO_3 using He^<**>(1s2s, 2^3S) shows that the lower-lying Co 3d-derived (main) bands are strongly suppressed relative to the O 2p-derived bands, reflecting the spatial distribution of the initial Co 3d wave-functions. On the other hand, the higher-lying Co 3d-derived (satellite) band is anomalously enhanced in the He^<**> spectrum. These findings are discussed on the basis of the initial and final configuration interactions, using Co_2O_<11> cluster.