Depth Sensitivity of Atomic Resolution Aberration-Corrected Through-Focus STEM Imaging of Bi Dopants on Cu Grain Boundaries

Abstract

A complete 3-dimensional view of materials at an atomic level has long been a goal of modern electron microscopy. Difficulties in obtaining 3-dimensinal images of materials at this high magnification level without the loss or distortion of information has been a challenge yet to be overcome [1]. The advent of an aberration-correction scanning transmission electron microscope (STEM) equipped with a cold fieldemission electron source has allowed much higher beam convergence angles to be utilized without parasitic aberration degrading image quality [2]. The benefit of using a higher beam convergence angle is two-fold: first, the higher convergence angle offers an improved lateral resolution as lateral resolution is inversely proportional to the beam convergence semi-angle, and second, the vertical resolution (along the optic axis) is improved as the vertical resolution is inversely proportional to the square of the beam convergence semi-angle. With these benefits large convergence angles are increasingly being used for STEM imaging in aberration-corrected systems.