High Resolution Powder Electron Diffraction in Scanning Electron Microscopy

Abstract

A modern scanning electron microscope equipped with a pixelated detector of transmitted electrons can record a four-dimensional (4D) dataset containing a two-dimensional (2D) array of 2D nanobeam electron diffraction patterns; this is known as a four-dimensional scanning transmission electron microscopy (4D-STEM). In this work, we introduce a new version of our method called 4D-STEM/PNBD (powder nanobeam diffraction), which yields high-resolution powder diffractograms, whose quality is fully comparable to standard TEM/SAED (selected-area electron diffraction) patterns. Our method converts a complex 4D-STEM dataset measured on a nanocrystalline material to a single 2D powder electron diffractogram, which is easy to process with standard software. The original version of 4D-STEM/PNBD method, which suffered from low resolution, was improved in three important areas: (i) an optimized data collection protocol enables the experimental determination of the point spread function (PSF) of the primary electron beam, (ii) an improved data processing combines an entropy-based filtering of the whole dataset with a PSF-deconvolution of the individual 2D diffractograms and (iii) completely re-written software automates all calculations and requires just a minimal user input. The new method was applied to Au, TbF3 and TiO2 nanocrystals and the resolution of the 4D-STEM/PNBD diffractograms was even slightly better than that of TEM/SAED.

Robust Local Thickness Estimation of Sub‐Micrometer Specimen by 4D‐STEM

“…Powder diffraction data were analyzed in STEMDIFF -powder electron diffraction in SEM available on the MathWorks File Exchange repository. [31] To replicate our results, settings shown in Table 2 should be used.…”

“…Specific information on, and identification of, these nanoparticles can be achieved with the recently-introduced 4D-STEM/PNBD method (powder nanobeam diffraction calculated from 4D-STEM data). [27,35] Ordinary SEM analytical techniques (such as STEM imaging and EDX analysis) could reveal the presence of TiO 2 , but they could not confirm the crystalline modification of TiO 2 nanoparticles. The new 4D-STEM/PNBD methods yields 2D powder electron diffractograms (Figure 5d,h) and their 1D radial profiles (Figure 5c,g).…”

Versatile domain mapping of scanning electron nanobeam diffraction datasets utilising variational autoencoders

“…The training data is then re-sampled using the Shannon entropy 38 of the processed patterns as an indicator of precipitate character. The Shannon entropy is a measure of information content in an image and is given by −∑ k p k ln(p k ), where p k is the frequency/probability of pixels of value k. Shannon entropy is used as the precipitate patterns are expected to have a higher entropy due to the additional diffraction information and is based on a similar application of Shannon entropy by Slouf et al 39 . The VAE was trained and the resulting latent-space clustered into two regions, which correspond to the precipitates and the background Al matrix.…”

Robust local thickness estimation of sub-micrometer specimen by 4D-STEM

“…We note that the thickness retrieved for the nanoparticles is not correct due to their atomic composition, density and crystallinity. Specific information on, and identification of, these nanoparticles can be achieved with the recently-introduced 4D-STEM/PNBD method (powder nanobeam diffraction calculated from 4D-STEM data) 33,34 . Ordinary SEM analytical techniques (such as STEM imaging and EDX analysis) could reveal the presence of TiO 2 , but they could not confirm the crystalline modification of TiO 2 nanoparticles.…”