The effects of probe characteristics and specimen thickness on the spatial resolution in the AEM

Abstract

In order to interpret the high-resolution x-ray microanalytical data generated by modern Analytical Electron Microscopes (AEM), it is necessary to understand the effects of the electron probe characteristics (size, current distribution) and the specimen thickness and composition on the spatial resolution. The spatial resolution obtained in a VG HB-501 dedicated Scanning Transmission Electron Microscope (STEM) has been determined over a range of specimen thicknesses and for different probe sizes. The experimentally determined spatial resolutions are compared with calculations based on the Gaussian beam broadening technique.The spatial resolutions were measured from composition profiles obtained from specimens which had abrupt changes in composition. Suitably heat treated 40wt%Ni- 30wt%Cr-Fe specimens consisted of precipitates of 80-90wt%Cr in a matrix of 25- 29wt%Cr. Composition profiles were obtained by stepping the electron probe across a precipitate/matrix interface. Accurate probe placement was achieved by computer control of the analysis positions in conjunction with software which corrected for specimen drift. Beam broadening in the specimen degrades the abrupt step change in composition into a continuous one with a finite width.