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

TL;DR

This study investigates the depth resolution of transmission Kikuchi diffraction (TKD) using a Zr-Nb alloy, revealing that signals originate from a depth approximately equal to the mean free path of thermal diffuse scattering, influencing grain structure observations.

Contribution

The paper provides a quantitative analysis of the depth sensitivity in TKD and offers guidelines for optimal sample thickness based on material symmetry and scattering properties.

Findings

Signals originate from a depth of about the mean free path of thermal diffuse scattering.

Surface sensitivity can cause different grain structures to be observed from opposite sides.

Recommended sample thicknesses are 6lambdaTDS for high symmetry and 3lambdaTDS for lower symmetry samples.

Abstract

In this paper, we have analysed 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 (lambdaTDS) 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 6lambdaTDS, or 21 times the elastic scattering mean free path (lambdaMFP) for samples of high crystal symmetry. For samples of lower symmetry, a smaller thickness 3lambdaTDS, or 10lambdaMFP is suggested.