Specimen‐thickness effects on transmission Kikuchi patterns in the scanning electron microscope

Abstract

SummaryWe report the effects of varying specimen thickness on the generation of transmission Kikuchi patterns in the scanning electron microscope. Diffraction patterns sufficient for automated indexing were observed from films spanning nearly three orders of magnitude in thickness in several materials, from 5 nm of hafnium dioxide to 3 μm of aluminum, corresponding to a mass-thickness range of ß5 to 810 μg cm -2 . The scattering events that are most likely to be detected in transmission are shown to be very near the exit surface of the films. The energies, spatial distribution and trajectories of the electrons that are transmitted through the film and are collected by the detector are predicted using Monte Carlo simulations.

On‐axis versus off‐axis Transmission Kikuchi Diffraction technique: application to the characterisation of severe plastic deformation‐induced ultrafine‐grained microstructures

“…The reason for this is the largely reduced interaction volume between the primary beam and the sample. The approach is also named transmission Electron Back-Scattered Diffraction (t-EBSD) or transmission Electron Forward Scatter Diffraction (t-EFSD) (Keller & Geiss, 2012;Brodusch et al, 2013a;Rice et al, 2014). Besides a sample holder designed for transmission, the TKD installation does not require additional equipment other than that used for the conventional EBSD system.…”

Nanostructure characterisation of flow-formed Cr–Mo–V steel using transmission Kikuchi diffraction technique

“…2, it was evident that the thickness of the TEM sample plays an important role in determining the quality of the diffraction patterns, thus the spatial resolution and resulting orientation measurements. Moreover, recently the effect of specimen thickness on generating transmission Kikuchi pattern in TKD is studied in detail in [31]. Using Monte Carlo simulation, the optimum sample thickness was predicted to be less than 1 μm for Al film using 30 kV incident beam energy with less than 10% of the incident electron reaching the detector [31].…”

“…Moreover, recently the effect of specimen thickness on generating transmission Kikuchi pattern in TKD is studied in detail in [31]. Using Monte Carlo simulation, the optimum sample thickness was predicted to be less than 1 μm for Al film using 30 kV incident beam energy with less than 10% of the incident electron reaching the detector [31]. It is also reported that for Al alloy, the optimum patterns were collected from a sample thickness ranging from 75 to 200 nm but with using relatively lower beam energies of 22 kV [24].…”

Techniques for Transmission EBSD Mapping of Atom Probe Specimens

“…Moreover, we will discuss challenges with the application of t-EBSD to the characterization of the inherently threedimensional specimens of interest for APT. Unlike conventional reflection EBSD, the mapped surface in transmission is the bottom surface [3], which can present unique difficulties in a specimen with multiple or overlapping grains that can cause overlapping or blurring of the Kikuchi patterns. We demonstrate this particular phenomenon in an APT specimen by mapping a sample with Atom Probe Assist™ mode with side-by-side grains and introducing a 90 degree rotation, such that only one pattern is visible.…”

“…Beam size changes across the cone-shaped APT specimen can be modeled to a first approximation with Monte Carlo simulations of electron trajectories. Our models [3] provide estimates of beam size and effective resolution at each point. Figure 2 shows the electron distribution at the exit surface for two different cases: (a) the beam impinging at the center of the tip 100 nm down the shank from the apex; and (c) the beam impinging at the center of the tip 500 nm down the shank from the apex.…”