Template masks for 4D-STEM

TL;DR

This paper introduces a novel template mask method for 4D-STEM that enhances atomic resolution imaging by correlating data with specific templates, enabling targeted visualization of atom columns.

Contribution

The paper presents a new correlation-based template mask technique for 4D-STEM, improving atomic column imaging over traditional user-defined masks.

Findings

Effective imaging of Li and O atom columns in LiFePO4

Imaging of O, Pb, and Ti across a domain wall in PbTiO3

Method is computationally straightforward and effective for moderate thickness specimens

Abstract

We present a new analysis method for atomic resolution four-dimensional scanning transmission electron microscopy (4D-STEM, in which a diffraction pattern is collected at each point of a raster scan of a focused electron beam across the specimen). In 4D-STEM, each measured intensity has a dual character, forming a pixel in a diffraction pattern and, equally, forming a pixel in a STEM image. Applying a mask to the data to obtain a "virtual" bright field or dark field image is widely used and understood. However, there is a complementary procedure, in which an image (template) is applied to the data to obtain a mask. This mask shows the correlation between the data and the template and, when applied to atomic resolution 4D-STEM data produces an image optimised for the template. This allows, for example, imaging of specific atom columns and is a significant improvement over user-defined masks such as virtual annular bright field imaging. We demonstrate the capability of the approach, separately imaging Li and O atom columns in LiFePO4 and O, Pb and Ti across a domain wall in PbTiO3.These template masks provide a computationally straightforward and general method to probe 4D-STEM data. They are particularly effective for specimens of moderate thickness where multiple scattering produces strong and specific correlations in diffraction patterns.