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

本研究旨在利用受激原子或离子撞击表面所发射的俄歇电子的衍射效应，发展一种表面结构分析技术。虽然我们的研究还没有达到这个目标，但我们已经获得了许多重要的结果，这些结果有助于解决表面和受激原子或离子之间电子跃迁过程中的基本和实际问题。(1)研究了受激原子撞击低功函数表面时的二次电子发射，提出了电子-空穴对形成级联中的热空穴衰变在E_F以上激发电子的机制。(2)亚稳诱导电子能谱已应用于许多表面体系，如氧/Ni(110)=氧诱导结构变化过程中电子态的变化；碱/硅（100）对碱金属表面氧化或氮化的促进或中毒作用。(3)建立了一套测量亚稳原子或离子诱导的弹丸速度分辨电子能谱的新光谱系统。快速He*原子到达非常接近表面的位置，这有效地扰乱了表面电子结构。对于慢He*原子，由于俄歇去激发通道，光谱中含有更高的电子贡献。(4)我们提出了二次响应理论的一种变体，它在等离子体频率附近或附近仍然有效，并证明了非线性本身可以限制等离子体振荡的幅度，从而提供了一种“非线性阻尼”机制。我们还将固体中电荷的非弹性散射截面与二次延迟密度响应函数的第2玻恩近似联系起来，由此推导出一个适用于描述电子和正电子能量损失谱的公式。

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.