Atomic‐Level Characterization of Grain‐Boundary Segregation and Elemental Site‐Location in Ni‐Base Superalloy by Aberration‐Corrected Scanning Transmission Electron Microscopy

Abstract

Chemical analysis at atomic-level spatial resolution with single-atom detection sensitivity is one of the ultimate goals in materials characterization. Such atomic-level materials characterization would be possible by electron energy-loss spectrometry (EELS) and X-ray energy dispersive spectrometry (XEDS) in aberration-corrected scanning transmission electron microscopes (STEMs) because more probe current can be added into the incident probe by aberrationcorrection. Using aberration-corrected STEMs, image resolution has already reached subAngstrom levels in high-angle annular dark-field (HAADF) imaging [e.g. 1]. For EELS analysis, sufficient amounts of core-loss signals can be generated within a short acquisition time by higher current probes, and hence atomic-resolution EELS mapping has already been applied [e.g., 2-4]. For XEDS analysis, spatial resolution reaches ~ 0.4 nm [5], which implies atomic-level analysis is feasible, in aberration-corrected STEMs. However, atomic-level chemical analysis is even more challenging in the XEDS approach since detection of X-ray signals is more limited than that in EELS (~100 times difference). The limited signals can be improved by applying spectrum-imaging (which records a full spectrum at individual pixels) in combination with multivariate statistical analysis (MSA) [6].