The effect of surface strain relaxation on HAADF imaging

In this work the effects of strain on high-angle annular dark field (HAADF) images taken in zone axis conditions have been quantitatively studied. In particular, the presence of dark contrast zones in experimental HAADF images of InGaAs-GaAs interfaces is here interpreted in terms of strain relaxation at the surface. The consistence of this assumption is demonstrated by means of experiments and simulations performed for different In compositions, specimen tilt and thickness conditions. It is shown how the HAADF contrast mechanism is related to the bending of the lattice planes in the first surface region. Finally, a generalization of the 1s approximation that is able to qualitatively describe the effect of strain on HAADF images is presented.