Diffraction of electrons Auger-excited by metastable-atoms or ions at the topmost surface layers and its application to surface structural analysis

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This research aims at developing a technique of surface structural analysis by utilizing the effect of diffraction of Auger electrons emitted by the impact of excited atoms or ions with the surface. Although our research is still short of this target, we have obtained many important results which contributes solving fundamental and practical problems in the electron transition processes between surfaces and excited atoms or ions.(1) We investigated the secondary electron emission upon impact of excited atoms at low-work function surfaces and proposed a mechanism of electron excitation above E_F through decay of hot holes in the cascade of electron-hole pair creation.(2) Metastable-induced electron spectroscopy has been applied to many surface systems, e.g., oxygen/Ni(110)=changes in the electronic states in the process of oxygen-induced structural change ; alkali/Si(100) promotion or poisoning effects by alkali metals on surface oxidation or nitridation.(3) A new spectroscopy system has been constructed which measures projectile-velocity resolved electron spectra induced by metastable atoms or ions. Fast He*atoms reach positions rather close to the, surface, which perturbs effectively the surface electronic structure. With slow He* atoms, the spectra contains higher contribution of electrons due to Auger de-excitation channel.(4) We proposed a variant of the quadratic response theory that remains valid near or at plasma frequency and demonstrated that the nonlinearity serves itself to restrict the amplitude of plasma oscillations, thus providing a mechanism of "nonlinear damping." We also related the cross section for the inelastic scattering of charges in solids in the 2nd Born approximation to the quadratic retarded density-response function, deriving by this a formula applicable to describe the electron and positron energy-loss spectroscopy.