Development of Electron Emission Microscope Using Metastable Atoms as Probe and Its Application to Studies of Solid Surfaces

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An electron emission microscope (EEM) using metastable atoms, low energy electrons, and photons as probes, has been developed and applied to the observation of various solid surfaces (surfaces of metals, semiconductors, thin organic films, etc.). Compared with the widely used microscopes such as the transmission electron microscope (TEM) and the scanning electron microscope (SEM), the EEM (1) provides information directly related to the electronic structure of the surface, (2) is selectively sensitive to the surface, and (3) scarcely destroys the surface.In contrast to other EEM, our new EEM has the following characteristics :(1) The electron optical system is kept under ultra-high vacuum for the purpose of the surface observation.(2) An energy analyzer included in the imaging system allows us to measure energy spectra in the surface micro-region and also to observe energy-selected images.(3) The EEM can be used as a metastable electron emission microscope (MEEM), low-energy electron e … More mission microscope (LEEM), and photoelectron emission microscope (PEEM) corresponding to three kinds of probes. The MEEM provides information on the outermost layr of the surface and the LEEM and PEEM give information on the top several layrs. Furthermore, the mirror electron microscope (MEM) using the electron probe, provides images reflecting the electrical potential of the surface.The central purpose of this study has been the development of the MEEM and this has been finally achieved : The MEEM images of the surface and the metastable atom electron spectrum (MAES) of the surface micro-region have been obtained for the first time. It has been shown that the MEEM enables us to observe sensitively the electronic state and the molecular orientation of the outermost layr in the micro-region of the surface.The MEEM is suitable for surfaces that are difficult to be observed by other microscopes (adsorbed surfaces, and surfaces of organic materials and biological systems), because, being introduced by thermal diffusion, metastable atoms have small velocity and scarcely destroy sample surfaces. Less