Interfacial Atomic Number Contrast in Thick TEM Samples

TL;DR

This paper models and demonstrates how atomic number contrast in thick TEM samples causes increased HAADF-STEM signals at interfaces, especially in samples over 100 nm thick, due to electron scattering effects.

Contribution

It introduces a probabilistic model incorporating elastic scattering and absorption to explain atomic contrast at interfaces in thick samples, validated by simulations and experiments.

Findings

Increased HAADF-STEM signal near interfaces in thick samples (>100 nm).

Signal enhancement extends up to 20 nm from the interface.

Simulation results agree with experimental TEM micrographs.

Abstract

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.