In recent years, there has been significant interest in using transmission Kikuchi diffraction (TKD) in scanning electron microscopes for studying ultra-fine grain and nanocrystalline materials and nanostructures. While absolute spatial resolutions of down to 5-10 nm have been attained 1 , the dependence of the achievable spatial resolution on the sample thickness is not well understood. Rice et al. 2 considered the effect of very high sample thicknesses on the spatial resolution, but focussed on the superiority of the technique compared to Electron Backscatter Diffraction (EBSD) rather than the absolute limits of TKD. Additionally, although it is known that the diffraction pattern largely originates from the bottom surface of the sample 3 , to date there has been little work on the depth resolution of TKD for different materials or tilts. This is an important consideration, as the depth resolution is expected to be highly material dependant, as it is in EBSD.
Here we have investigated the impact of sample thickness and tilt on the spatial and depth resolution of TKD in aluminium and copper. The absolute spatial resolution was measured by observing the quality of diffraction patterns on either side of a grain boundary for different sample thicknesses. We will present experimentally-determined depth resolution measurements. These are achieved by using samples in which layers of different thicknesses of nanocrystalline material are sputtered onto an electropolished coarse-grained substrate. The depth resolution measurements obtained are the thickness at which the nanocrystalline signal becomes dominant and where the signal from the substrate disappears.