MEED study of some crystalline surfaces

Abstract

A new medium energy electron diffraction (MEED) system, which can observe both back scattering (BSMEED) and forward scattering (RMEED) patterns from the same surface of crystalline solids has been designed. Results obtained from MgO(001) and GaAs(001) indicate that MEED has the following favourable characteristics: (1) Unlike LEED, post-acceleration of the diffracted beam with a grid is not necessary for MEED. The diffraction pattern can be seen directly on a fluorescent screen. (2) Collimation and focusing of the incident beam are readily achieved and sharp diffraction spots are observed. (3) Unlike RHEED, a strictly flat surface is not necessary for MEED. Relatively rough, but clean surfaces can produce diffraction patterns. (4) From Kikuchi lines or bands it is possible to determine the precise orientation of the crystal surface. (5) By changing the energy of the incident beam it is possible to observe the surface layer both in two and three dimensions.