Spatial Resolutions of On-Axis and Off-Axis Transmission Kikuchi Diffraction Methods

Abstract

Spatial resolution is one of the key factors in orientation microscopy, as it determines the accuracy of grain size investigation and phase identification. We determined the spatial resolutions of on-axis and off-axis transmission Kikuchi diffraction (TKD) methods by calculating correlation coefficients using only the effective parts of on-axis and off-axis transmission Kikuchi patterns. During the calculation, we used average filtering to evaluate the spatial resolution more accurately. The spatial resolutions of both on-axis and off-axis TKD methods were determined in the same scanning electron microscope at different accelerating voltages and specimen thicknesses. The spatial resolution of the on-axis TKD was higher than that of the off-axis TKD at the same parameters. Furthermore, with an increase in accelerating voltage or a decrease in specimen thickness, the spatial resolutions of the two configurations could be significantly improved, from tens of nanometers to below 10 nm. At a voltage of 30 kV and sample thickness of 74 nm, both on-axis and off-axis TKD methods exhibited the highest resolutions of 6.2 and 9.7 nm, respectively.

Comparison of Orientation Mapping in SEM and TEM

“…This difference is largely caused by the thickness of the beam-induced contamination that develops during acquisition and no significant differences between the electron optics or detector configurations. While it has been shown previously that the spatial resolution difference between off-axis (conventional) and on-axis (horizontal) TKD can be as large as 10 nm (Shen et al, 2019), the unindexed pixels here do not appear to be the result of a limited spatial resolution. Some unindexed pixels may be a result of the extreme gnomonic projection distortion that is caused by the sample and detector geometry used with a vertical phosphor screen.…”

Local Kikuchi band detection in electron backscatter diffraction patterns for enhanced pattern indexing

“…However, low‐quality patterns are always inevitable, which could mainly be divided into two classes: (i) noisy patterns, which can be termed as patterns with lower signal‐to‐noise ratio and low intensity. This kind of patterns arise from the large interaction volume, 8,9 high acquisition speed of camera 10 or insufficient preparation of samples. (ii) Patterns with partially missing bands, which means that the quality of majority regions of the pattern is high, but some Kikuchi bands are partially missing.…”