Development of diffracted electron spectroscopy in RHEED and its application to structural and morphological study on crystal surface

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Newly improved energy-filtered reflection high-energy electron diffraction apparatus has been constructed, which is combined with energy-loss measurement system using channeltron detector, high frequency modulation of retarding voltage and lock-in amplifier. The modulation amplitude with frequency of ω is superimposed on the retarding voltage. Transmitted electron beam passing through the energy filter is detected by the movable channeltron. The amplified electron beam current is finally inputted to lock-in amplifier. When the signal component of frequency ω is outputted from the lock-in amplifier, the energy-differentiated spectra, conventional energy loss spectra, are directly obtained.Using this apparatus, energy loss spectra of specularly reflected electron beam have been measured for Si(111)7x7 surface and In over-layer on it. The obtained results are summarized as follows. 1. For Si(111)7x7 surface, the averaged number of surface plasmon excitations changes in proportion to 1/sin θ /where θ denotes the glancing angle. It has been confirmed that the experimentally obtained coefficient of 1/sin θ nearly agree with the theoretical value calculated by Lucas. 2. Especially, it has been found for the first time that the number of surface plasmon excitations abnormally increases at θ = 4° for [11-2] azimuth due to diffraction condition. 3. Surface plasmon energy of Si, 11.7 eV, hardly changes even for 1 monolayer coverage of In. Over 1 monolayer, the energy value gradually decrease and becomes constant value of 10.4 eV, at about 30A deposition thickness. The energy value is still larger than the surface plasmon energy of In, 8.9 eV, and nearly corresponds to the middle of Si and In surface plasmon energies, which is considered to be strongly influenced by the interface region between Si and In.The EF-RHEED apparatus combined with the energy loss measurement system will become powerful tool for unknown inelastic scattering field in RHEED.