Interface location by depth sectioning using a low-angle annular dark field detector

We investigate the application of a highly convergent aberration-corrected electron probe to the determination of depth-related features of layered heterostructures. By centring the probe upon an atomic column and varying defocus, we obtain a depth-scan of the signal from a low-angle annular dark field (LAADF) detector. Peaks associated with the heterojunctions and crystal surfaces are observed which allow for the sample thickness and heterojunction locations to be determined. Channelling of the electron wave function along atomic columns is shown to play an important role in the production of these peaks, whose presence at all interfaces is shown to rely on a combination of elastic and thermal diffuse scattering signals.

► A highly convergent electron probe can locate buried layers in heterostructures.
► Varying defocus, signal from an atomic column is monitored in a LAADF detector.
► Peaks associated with the heterojunctions and crystal surfaces are observed.
► Channelling along atomic columns is important in producing these peaks.
► The peaks are due to both elastic and thermal diffuse scattering signals.