THEORETICAL AND EXPERIMENTAL STUDIES OF ELECTRON RESONANCE EFFECTS IN REFLECTION HIGH-ENERGY ELECTRON-DIFFRACTION

The electron resonance effect for 100 keV electrons incident on the surface of GaAs (110) in RHEED is studied by theoretical simulations using multislice theory and experimental observations. The exact resonance conditions, effective resonance region, effective penetration depth of electrons at or near the resonance condition and scattering processes involved for the resonance effect are investigated. It is found that the intensity of the 440 specularly reflected beam is mainly due to direct reflection from the surface atomic layer and beam enhancement due to surface channeling effects under the resonance conditions seems to be insignificant. For the 880 specularly reflected beam most of the electron intensity penetrates the surface and is diffracted by the crystal. The resonance condition for the 880 specular beam is satisfied when the transmitted beam excites a strong surface wave which propagates in the direction parallel or nearly parallel to the surface and is localized in the surface region by the surface potential barrier; double diffraction from the surface beam to the specular beam then enhances the total intensity in the specular beam. The exact resonance condition for the 880 beam is found to be at the glancing angle of 35.7 mrad and the azimuth angle of 29.7 mrad. A strong wave field is localized in the surface region at the resonance condition with an effective electron penetration depth of approximately 5 angstrom, which increases to approximately 35 angstrom on going to the nonresonance conditions. The effective resonance region for the 880 spot is approximately 2 mrad about the azimuth angle and approximately 1 mrad about the glancing angle.