Tracking the Picoscale Spatial Motion of Atomic Columns During Dynamic Structural Change

TL;DR

This paper introduces a Gaussian fitting algorithm for tracking atomic columns in high-frame-rate TEM images, enabling millisecond resolution analysis of dynamic atomic structural changes in nanoparticles.

Contribution

The authors develop and validate a robust 2D Gaussian fitting method for analyzing atomic motion in TEM image series, improving accuracy over traditional centroid techniques.

Findings

Algorithm accurately tracks atomic columns in noisy TEM data.

Intensity measurement accuracy depends on electron dose per frame.

Method applicable to various temporally resolved TEM datasets.

Abstract

In many materials systems, such as catalytic nanoparticles, the ability to characterize dynamic atomic structural changes is important for developing a more fundamental understanding of functionality. Recent developments in direct electron detection now allow image series to be acquired at frame rates on the order of 1000 frames per second in bright-field transmission electron microscopy (BF TEM), which could potentially allow dynamic changes in the atomic structure of individual nanoparticles to be characterized with millisecond temporal resolution in favourable cases. However, extracting such data from TEM image series requires the development of computational methods that can be applied to very large datasets and are robust in the presence of noise and in the non-ideal imaging conditions of some types of environmental TEM experiments. Here, we present a two-dimensional Gaussian fitting algorithm to track the position and intensities of atomic columns in temporally resolved BF TEM image series. We have tested our algorithm on experimental image series of Ce atomic columns near the surface of a ceria (CeO2) nanoparticle with electron beam doses of ~125-5000 e-{\AA}-2 per frame. The accuracy of the algorithm for locating atomic column positions is compared to that of the more traditional centroid fitting technique, and the accuracy of intensity measurements is evaluated as a function of dose per frame. The code developed here, and the methodology used to explore the errors and limitations of the measurements, could be applied more broadly to any temporally resolved TEM image series to track dynamic atomic column motion.