On the depth resolution of transmission Kikuchi diffraction (TKD) analysis

Ultramicroscopy. 2019 Oct:205:5-12. doi: 10.1016/j.ultramic.2019.06.003. Epub 2019 Jun 10.

Abstract

In this paper, we have analyzed the depth resolution that can be achieved by on-axis transmission Kikuchi diffraction (TKD) using a Zr-Nb alloy. The results indicate that the signals contributing to detectable Kikuchi bands originate from a depth of approximately the mean free path of thermal diffuse scattering (λTDS) from the bottom surface of a thin foil sample. This existing surface sensitivity can thus lead to the observation of different grain structures when opposite sides of a nano-crystalline foil are facing the incident electron beam. These results also provide a guideline for the ideal sample thickness for TKD analysis of ≤ 6λTDS, or 21 times the elastic scattering mean free path (λMFP) for samples of high crystal symmetry. For samples of lower symmetry, a smaller thickness ≤ 3λTDS, or ≤ 10λMFP is suggested.

Keywords: Depth resolution; Nanocrystalline material; Thermal diffuse scattering; Transmission Kikuchi diffraction (TKD); Zr alloys.