Abstract
The interface atomic structure of a A1(001)/GaAs(001) bicrystal with a high density of misfit dislocations is derived by two dynamical diffraction techniques. Firstly, analysis of contrast in higher-order Laue zone (HOLZ) discs yields information on excitation amplitudes of successive Bloch wave states associated with the fast electron wavefunction in the underlying GaAs layer, and how these vary with rigid shift and position between misfit dislocations. Secondly, characteristic X-ray emission is recorded in energy-dispersive X-ray spectra under varying 220 systematic row diffraction conditions, and changes in emission rates from Al, Ga and As are monitored as a function of orientation (similar to an atom location by channelling-enhanced microanalysis (ALCHEMI)). We base our analysis on changes in Bloch wave branch amplitudes induced in GaAs with a rigid shift of the top A1 layer, together with additional displacements due to a periodic array of interfacial ™14<110> dislocations. The influence of the interfacial dislocation network on both HOLZ and the ALCHEMI results is found to be small for the observed dislocation spacing of 17O Å. However, misfit dislocations may provide a strong perturbation and render theory based on an undislocated interface invalid for spacings less than 50 Å. Both the HOLZ and the ALCHEMI results support the rigid-shift model which projects A1 atoms onto open channels in the GaAs<001> structure, in agreement with previous observations.