  The atomic number contrast imaging technique reveals an increase in intensity
at interfaces of a high and low-density material in case of relatively thick
samples. Elastic scattering factors and absorption coefficients are
incorporated in a probabilistic model to study atomic contrast occurring at the
interface of two materials when the High-Angle Annular Dark-Field (HAADF)
detector is used in the Scanning TEM (STEM) mode. Simulations of thick samples
reveal that electrons traverse from a higher density material to a lower
density material near the interface which increases the HAADF-STEM signal. This
effect is more dominant in TEM samples of thickness greater than 100 nm and the
increase in signal occurs up to 20 nm from the interface. The behavior of
electrons near the interface is explained by comparing the simulation results
with experimental TEM micrographs in the HAADF-STEM mode.
