The Interpretation of Ptychographical Reconstructions from Sphalerite Structures

Ptychography is an electron diffraction technique in which Bragg reflections are interfered coherently in order to measure the phases of diffraction orders directly. Two simple reconstruction methods exist, which require different degrees of coherence in the illuminating electron beam. Simulations on InP <110> for two electron accelerating voltages suggest that the asymmetric ‘dumbbells’ can be reconstructed for small thicknesses, but that the reconstruction methods break down at thicknesses around 10 nm. At larger thicknesses one reconstruction method yields images which show the phosphorus atom. The phase object approximation is shown to break down at thicknesses of about 3.3 nm.