A method for computing grazing-incidence backscattering medium energy
(1-3 keV) electron diffraction (GBMEED) is presented. The technique wa
s recently proposed as a structural tool exhibiting diffraction effect
s resembling those of XPD. In GBMEED the intensity of quasielastically
thermal diffuse scattering is measured at large scattering angles suc
h that different atoms can be assumed to vibrate independently, and th
us represent localized sources for diffuse scattering in the surface l
ayers. The basis of the calculations is the multiple scattering theory
of diffuse RHEED adopted to the medium energy case with a vibrating a
tom as source of diffuse scattering. Calculated plots of the intensity
versus azimuthal/polar exit angle for an In overlayer on Si(111) show
the forward focusing effect along the source-scatterer direction (wel
l known from XPD) and further fine structure.