<br/>Many processes in materials science, chemistry and biology take place at interfaces in a liquid environment – such as chemical conversions, the synthesis of nanoparticles, the operation of Li-ion or next generation batteries, and cellular functions. Often the final desired outcome is a result of a series of complicated transients, where a change in the order, magnitude or location in each of the steps in the process can lead to a radically different result. Understanding and subsequently controlling the process therefore requires the ability to directly observe the transients as they happen. Aberration Corrected (Scanning) Transmission Electron Microscopy ((S)TEM) has the spatial resolution to directly visualize these transient processes on the atomic scale. However, the increased current densities caused by the advent of the correctors have made beam damage more prevalent and the limitation to imaging using <i>operando</i> liquid cells is now the sample rather than microscope. The aim now is therefore to more efficiently use the dose that is supplied to the sample and to extract the most information from each image. Optimizing the dose/data content/speed in non-traditional ways (i.e. not just simply lowering the beam current) involves two main strategies to achieve dose fractionation and distribution – reducing the number of pixels being sampled in STEM mode (thereby distributing dose and increasing speed), or increasing the acquisition speed of the images in TEM mode. For the case of the STEM, inpainting methods allow a reduction in the number of pixels by of an order of magnitude or more, allowing data speed to be automatically increased and images recorded in a compressed form. For the TEM mode of operation, an increase in speed increases the number of images and means that compressive sensing and automated methods of tracking changes in the structure need to be developed so that only the important changes are automatically detected and recorded. In this presentation, the basic approach to dose control using both conventional and unconventional sampling methods will be described. Results demonstrating these methods to quantitatively study the kinetics of nanoscale dynamic processes involving electrochemical driving forces will be presented.

Imaging dynamic processes in liquids by scanning transmission electron microscopy (STEM)

2019 Fall National Meeting

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