DETECTOR GEOMETRY, THERMAL DIFFUSE-SCATTERING AND STRAIN EFFECTS IN ADF STEM IMAGING

Intensities of atomic-resolution Annular Dark Field Scanning Transmission Electron Microscopy (ADF STEM) images of zone-axis-oriented specimens change with defocus at rates that depend on lattice spacing. Thickness and strain effects on the intensities have been demonstrated. In this paper, image simulations (with some experimental basis) are presented that consider the dimensions of the ADF detector. Changing the inner radius of the detector seems to have relatively small effect on the image except to lower the detected intensity. Probe size was explored and a case identified where multiple scattering was important in the image. Thermal diffuse scattering (TDS) is important in high-angle scattering at room temperatures but it does not seem to alter the image appearance markedly. Finally, the image arising from the strain field around a single boron atom has been simulated and the results suggest increased scattering in agreement with observations. This mechanism may be adequate for single impurity atom detection at low temperatures and with special detector angles.