Strain in crystals can be measured through the evaluation of geometric phase of selected diffracted beams (e.g. (220) and (002)
beams in silicon ) by off-axis electron holography technique. The principle of this measurement is based on Moire fringes observed between two lattices.
By using off-axis holography, the electron beam from the lattice of the substrate can interfere with that of the lattice in the device region for strain mapping. With the application of aberration correctors, a picometer precision can be achieved to map 2D strain distribution. 
With the electron holography technique, the direct correlation between the phase and crystal potential for strain analysis can only be valid in very thin specimens, and this approximation breaks down rapidly in thick specimens.
 M.J. Hÿtch, F. Houdellier, A. Claverie, and L. Clément, Comparison of CBED and Dark-field Holography for Strain Mapping in Nanostructures and Devices, 2009. ESSDERC '09. Proceedings of the European Solid State Device Research Conference, (2009) 307 - 310.
 Kimoto K, Asaka T, Yu XZ, Nagai T, Matsui Y, Ishizuka K (2010) Local crystal structure analysis
with several picometer precision using scanning transmission electron microscopy.