Bright-field scanning confocal electron microscopy using a double aberration-corrected transmission electron microscope

Scanning confocal electron microscopy (SCEM) offers a mechanism for three-dimensional imaging of materials, which makes use of the reduced depth of field in an aberration-corrected transmission electron microscope. The simplest configuration of SCEM is the bright-field mode. In this paper we present experimental data and simulations showing the form of bright-field SCEM images. We show that the depth dependence of the three-dimensional image can be explained in terms of two-dimensional images formed in the detector plane. For a crystalline sample, this so-called probe image is shown to be similar to a conventional diffraction pattern. Experimental results and simulations show how the diffracted probes in this image are elongated in thicker crystals and the use of this elongation to estimate sample thickness is explored.

Research Highlights
► The confocal probe image in a scanning confocal electron microscopy image reveals information about the thickness and height of the crystalline layer.
► The form of the contrast in a three-dimensional bright-field scanning confocal electron microscopy image can be explained in terms of the confocal probe image.
► Despite the complicated form of the contrast in bright-field scanning confocal electron microscopy, we see that depth information is transferred on a 10 nm scale.