Dynamic Observation of Outermost Surface Layer Reactions by Metastable Electron Emission Microscope

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In this study we tried to observe the adsorption and diffusion of molecules, and dynamic processes of two-dimensional reactions between molecules on a well-defined solid surface, using the metastable electron emission microscope (MEEM) recently developed at our laboratory. This microscope images electrons emitted from the solid surface by impact of metastable atoms by means of an electron lens system. The results of the study are as follows.(1) A COD camera was directly connected to the MCP detection part of the MAES apparatus. A new data analysis system combined with the camera enabled us to observe MEEM images sensitively by processing the images.(2) Substrates (surfaces of silicon single crystals, cleavage planes of graphite and MoS_2 crystals, diamond films, etc.) were cleaned by heating. The process of the cleaning was observed by LEED (low energy electron diffraction), EELS (electron energy loss spectroscopy) and MAES (metastable atom electron spectroscopy).(3) The samples of org … More anic compounds (phthalocyanines, PTCDA (perylene-tetracarboxy1ic- dianhydride), etc.) were deposited by vacuum sublimation onto the above substrates. The change of the films with the elapse of time and the diffusion process of molecules were observed by MEEM (giving PIES in the micro-local area and energy-filtered images) and LEEM (giving EELS in the micro-local area and energy-filtered images).(4) The similar observations as above were carried out by PIES (Penning ionization electron spectroscopy), ARUPS (angle-resolved ultraviolet photoelectron spectroscopy), and HREELS (high-resolution electron energy loss spectroscopy) on ordinary surface-analysis apparatuses.(5) Samples of two kinds (organic compound and metal such as In) were deposited onto the substrates. The two-dimensional reactions between the samples were observed.(6) On the basis of the above results, the reaction rate, the position of the reaction in the molecule, and dynamic process in the change of the electronic state were clarified. Less