High Resolution Powder Electron Diffraction in Scanning Electron Microscopy.

Miroslav Slouf,Vladislav Krzyzanek,Radim Skoupy,Ewa Pavlova

doi:10.3390/ma14247550

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.

Highlights

Scanning electron microscopy (SEM) is a well-established method for characterization of materials in both micro- and nanoscale
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Summary

Introduction

Scanning electron microscopy (SEM) is a well-established method for characterization of materials in both micro- and nanoscale. The classical modes of SEM comprise imaging with secondary electrons (SE), backscattered electrons (BSE) and transmitted electrons (scanning transmission electron microscopy; STEM), and microanalysis (energy-dispersive analysis of X-rays; EDX). In the field of STEM, the standard detectors collect just the integral signal from the electrons going through the specimen almost directly (bright field imaging, BF) or from the electrons scattered at higher angles (annular dark field imaging, ADF, and high-angle annular dark field imaging, HAADF). The fact that STEM imaging might yield more information, on the condition that it was possible to record positions of the scattered electrons, did not escape the attention of researchers.

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