SEM-based Transmission Kikuchi Diffraction (SEM-TKD) [1,2] is an extension to the conventional  technique of reflection EBSD (using bulk samples) to transmision EBSD using thin samples.  The main advantage of SEM-TKD over the conventional method is a large improvement in spatial resolution of point-analysis from small particles and of mapping data from thin films.

This improvement is primarily a consequence of examining thin, electron-transparent TEM samples in transmission, which reduces the effective diffraction and escape volume, as well as the use of zero- to low sample tilts which reduces anisotropic beam-spreading effects.  The technique is used to produce 2D datasets from flat, thin sample areas.  This data is then used for microstructural analysis including crystallographic orientation, grain size, phase distribution, and grain boundary character and distribution.  It is especially useful in characterizing highly-strained materials and materials with grain sizes under 50nm.

A significant attraction of TKD is that these improvements can be realised using conventional EBSD hardware, in its conventional position on the SEM, without any modification.  However, for TKD the sample position, pattern centre (high up or above the detector screen) and sample tilt (close to horizontal) are very different to those required for conventional EBSD (just above the screen centre line, and 70° respectively).  Thus the TKD-mode imposes a more extreme case of the gnomonic projection which is already inherent to the capture of conventional electron backscatter patterns.

The most notable effects of the TKD projection geometry are that horizontal bands near to the bottom of the screen are imaged wider than normal, and that the non-symmetric intensity across these bands is highlighted (as illustrated in Figure 1).

Here we discuss how these distortions affect analysis using a conventional EBSP solving engine and some new technology developed to improve performance.

References:

[1] R.R. Keller, R.H. Geiss, Transmission EBSD from 10nm domains in a scanning electron microscope, Journal of Microsopy 245 (2012) 245-251

[2] Trimby, P.W., Orientation mapping of nanostructured materials using transmission Kikuchi diffraction in the scanning electron microscope, Ultramicrosopy 120 (2012) 16-24

Figures:

Figure 1 A EBSD pattern, illustrating the impact of TKD projection geometry. The horizontal bands near to the bottom of the screen are imaged wider than normal, and there is a non-symmetric intensity across these bands.

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EMC Abstracts - https://emc-proceedings.com/abstract/transmission-kikuchi-diffraction-effective-nano-scale-analysis-using-conventional-ebsd-hardware/