Bragg diffraction imaging of defects at crystal surfaces

Scanning Bragg diffraction images of lattice defects are calculated for a medium energy electron beam at grazing incidence. A stacking fault intersecting the surface introduces additional dynamical beams which interfere to produce a band of fringes near the fault. A dislocation emerging at the surface perturbs the local lattice orientation and therefore changes the reflected beam intensities. It is shown that for a probe size of 10 A the contrast for these defects is about 50 percent while the reflected intensity is 1-10 percent of the incident intensity.