Quantification and optimization of ADF-STEM image contrast for beam-sensitive materials

Abstract

Many functional materials are difficult to analyse by scanning transmission electron microscopy (STEM) on account of their beam sensitivity and low contrast between different phases. The problem becomes even more severe when thick specimens need to be investigated, a situation that is common for materials that are ordered from the nanometre to micrometre length scales or when performing dynamic experiments in a TEM liquid cell. Here we report a method to optimize annular dark-field (ADF) STEM imaging conditions and detector geometries for a thick and beam-sensitive low-contrast specimen using the example of a carbon nanotube/polymer nanocomposite. We carried out Monte Carlo simulations as well as quantitative ADF-STEM imaging experiments to predict and verify optimum contrast conditions. The presented method is general, can be easily adapted to other beam-sensitive and/or low-contrast materials, as shown for a polymer vesicle within a TEM liquid cell, and can act as an expert guide on whether an experiment is feasible and to determine the best imaging conditions.

Unhindered Brownian Motion of Individual Nanoparticles in Liquid-Phase Scanning Transmission Electron Microscopy

“…The liquid thickness is beyond the inelastic mean free path, 45 which leads to STEM contrast inversion from multiple scattering causing the Au particles to appear dark (Figure 1b, Supporting Information Note 6). 46,47 In order to minimize electron-beam effects on NP dynamics, we used electron fluxes of 0.14 − 3.5 e − /(Å 2 × s). These fluxes (Supporting Information Note 6) are low compared to typical values of 1 − 100e − /(Å 2 × s) in the LPTEM literature focusing on NP dynamics.…”

Electroanalytical methods and their hyphenated techniques for novel ion battery anode research

“…For this, a focused electron beam is scanned across the sample, and the transmitted electrons scattered from each point of the raster are recorded by an annular detector to form a dark-field STEM image. 112 The obtained results indicated a two-step lithiation pathway through Li intercalation and Cu extrusion.…”

Development of a Practicable Digital Pulse Read-Out for Dark-Field STEM

“…For high-resolution imaging this would usually be in electrons per square Angstrom (e − /Å 2 ). Under typical conditions, it is not uncommon to use ∼10 8 e − /Å 2 while imaging stable samples (Gnanasekaran et al, 2018); however, this is maybe a million times too high for fragile samples (Buban et al, 2010). For example, zeolites and organic single crystals show damage starting from the order of 100 e − /Å 2 , with some examples of the latter damaging at doses far less than this (Revol & Manley, 1986;Pan & Crozier, 1993;S'ari et al, 2019).…”