Kinematic HAADF-STEM image simulation of small nanoparticles

D.S He,Z.Y Li,J Yuan

doi:10.1016/j.micron.2015.04.005

Abstract

The high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) has been widely used in nanoparticle characterization due to its relatively straightforward interpretability, although multislice simulation is often required in order to take into account the strong dynamical screening effect if quantitative structure information is needed. The multislice simulation is very time-consuming, which can be a hurdle in cases when one has to deal with a large set of images. In this paper, we introduce a simple computer program, based on kinematic-scattering method, which allows users to simulate HAADF-STEM images of small nanoparticles, in ‘real time’ on a standard desktop computer. By comparing with the sophisticated multislice simulation, we demonstrate that such an approach is adequate for nanoparticles of ∼3nm in diameter (assuming an approximately spherical shape), particularly away from strict zone axis conditions. As an application, we show that the efficient kinematic simulation allows quick identification of orientation of nanoparticles.

Highlights

The high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) is one of the high-resolution electron microscopy techniques that benefits most from the recent technical improvement of the aberration corrector (Haider et al, 1998), pushing the lateral resolution reliably to sub Angstrom (Nellist et al, 2004)
Differing from the conventional transmission electron microscopy (CTEM), where the specimen is illuminated by a parallel broad beam (Wang, 2000), HAADF-STEM uses a sharply focused beam to scan across the specimen and the annular dark field (ADF) detector collects only the scattered electrons
The increasingly wide availability of the state-of-art HAADF-STEM means that the image simulation is, in many cases, the bottleneck for understanding the three dimensional structure of nanoparticles

Summary

Introduction

The high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) is one of the high-resolution electron microscopy techniques that benefits most from the recent technical improvement of the aberration corrector (Haider et al, 1998), pushing the lateral resolution reliably to sub Angstrom (Nellist et al, 2004). The increasingly wide availability of the state-of-art HAADF-STEM means that the image simulation is, in many cases, the bottleneck for understanding the three dimensional structure of nanoparticles. This is especially problematic in the case of studying the dynamic behavior of nanoparticles where usually a large number of images of the nanoparticles are required and their interpretation requires comparison of the image simulation with the suitable model atomic structures. This is a time-consuming process and especially so for many researchers who have limited access to supercomputing facilities. The software package is available as a stand-alone code, free on request by contacting the corresponding authors of this paper

Mathematic model of kinematic simulation

Design of the software

Case studies

E Accelerating voltage Source size Oversampling

Orientation dependence

Z-contrast imaging and simulation

Conclusion