Accurate Evaluation of Aberration for Probe-Forming System and Influence of Aberration on High-Resolution STEM image

Hidetaka Sawada,Fumio Hosokawa,Angus I Kirkland

doi:10.1088/1742-6596/902/1/012012

Abstract

The influence of residual three-fold astigmatism on high-resolution STEM imaging of graphene has been investigated. The aberration was measured by the segmented Ronchigram auto-correlation function method using the graphene lattice. In the presence of residual threefold astigmatism the graphene lattice showed a lower three-fold rotational symmetry where three C atoms in the six membered ring had a higher intensity.

Highlights

Aberration corrected instruments are commonly used to obtain high-resolution imaging in both STEM and TEM [1,2], and single atoms of light elements including boron, carbon, nitrogen, and oxygen can be imaged in two-dimensional materials
The aberration was measured by the segmented Ronchigram auto-correlation function method using the graphene lattice
It is useful to understand the influence of this aberration directly on high-resolution STEM images and we have evaluated its effects using STEM images of monolayer graphene

Summary

Introduction

Aberration corrected instruments are commonly used to obtain high-resolution imaging in both STEM and TEM [1,2], and single atoms of light elements including boron, carbon, nitrogen, and oxygen can be imaged in two-dimensional materials. During high-resolution image observation it is possible to manually correct first-order defocus and two-fold astigmatism to optimize these aberration. Second-order three-fold stigmatism is not easy to correct manually by observing a high-resolution image or a Ronchigram. We have developed a method to measure this aberration using a two-dimensional lattice [6] Using this method, a high-resolution image of a twodimensional material and the aberration measurement can be performed with the same probe-forming condition and the same specimen. 2. Aberration measurement and high-resolution observation of graphene Ronchigrams from an amorphous film (Fig.1(a)) and from monolayer graphene ((Fig.1(b)) were recorded using a JEM-ARM300F equipped with a STEM spherical aberration corrector at an accelerating voltage of 80 kV.

A4: Four-fold astigmatism

Conclusion