Abstract
Transmission Kikuchi diffraction (TKD) has been gaining momentum as a high resolution alternative to electron back-scattered diffraction (EBSD), adding to the existing electron diffraction modalities in the scanning electron microscope (SEM). The image simulation of any of these measurement techniques requires an energy dependent diffraction model for which, in turn, knowledge of electron energies and diffraction distances distributions is required. We identify the sample-detector geometry and the effect of inelastic events on the diffracting electron beam as the important factors to be considered when predicting these distributions. However, tractable models taking into account inelastic scattering explicitly are lacking. In this study, we expand the Monte Carlo (MC) energy-weighting dynamical simulations models used for EBSD [1] and ECP [2] to the TKD case. We show that the foil thickness in TKD can be used as a means of energy filtering and compare band sharpness in the different modalities. The current model is shown to correctly predict TKD patterns and, through the dictionary indexing approach, to produce higher quality indexed TKD maps than conventional Hough transform approach, especially close to grain boundaries.
Highlights
Electron diffraction techniques in the scanning electron microscope (SEM) are established and versatile tools for microstructural investigation of crystalline materials
The master pattern expression in Eq (2) reveals that electron back-scattered diffraction (EBSD), electron channeling patterns (ECPs), and Transmission Kikuchi diffraction (TKD) master patterns have a lot in common; in particular, the dynamical scattering process that underlies the generation of Kikuchi bands is identical for the three diffraction modalities
The only differences occur in the directional, depth, and energy distributions of the B/forward-scattered electrons (FSEs) that contribute to the patterns
Summary
Electron diffraction techniques in the scanning electron microscope (SEM) are established and versatile tools for microstructural investigation of crystalline materials. Dynamical diffraction modelling is applied for the full MC predicted electron energy and path distributions We extend this model to TKD patterns by considering the geometry of a thin film sample where the entry (top) and escape (bottom) surfaces are different such that the incoherent events acting as sources of diffracting electrons are scattering in a forward direction. While this approach may not take into account the full extent of inelastic scattering effects on diffracted electrons proposed by the Yoshioka equations, it leads to a model of manageable complexity which is straightforward to implement and whose predictions are understood.
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