Electron Tomography of ZnO Nanocones with Secondary Signals in TEM

Abstract

Electron tomography, which has been successfully utilized in life sciences, has attracted attention in materials science recently. Z-contrast imaging using a High Angle Annular Dark Field (HAADF) detector and Energy Filtered Transmission Electron Microscopy (EFTEM) imaging have been proved to be applicable in tomographic studies provided that the contrast in the image is only due to a change in mass-thickness of the investigated sample but not the crystallographic orientation [1]. However, for these imaging modes, the thickness of the sample is the main constraint in determining the reliability of the reconstructions. Especially HAADF Scanning TEM imaging is highly sensitive to thickness variations which makes it almost impossible to use this technique for materials thicker than a couple of hundreds of nanometres. As the thickness increases, the number of electrons transmitted decreases, therefore, using the backscattered and secondary electrons become more effective.