Structural fingerprinting of nanocrystals in the transmission electron microscope

Abstract

It is well known that nanocrystals cannot be fingerprinted structurally from laboratory based powder X-ray diffraction patterns. Three novel strategies for the structurally identification of nanocrystals in a transmission electron microscope (TEM) are, therefore, presented. Either a single High-Resolution Transmission Electron Microscopy (HRTEM) image or a single Precession Electron Diffractogram (PED) can be employed. The structural identification information is in both cases collected from an individual nanocrystal. PED from fine-grained crystal powders may also be utilized. Automation of the former two strategies shall lead to statistically significant results on ensembles of nanocrystals and is currently in progress. The structural information that can be extracted from a HRTEM image of an approximately 5 to 10 nm thick nanocrystal is the projected reciprocal lattice geometry, the plane symmetry group, and a few structure factor amplitudes and phase angles. While the structure factor amplitudes suffer from dynamical diffraction effects and are in addition modified by the (not precisely known) contrast-transfer function of the objective lens, the structure factor phase angles are remarkably stable against dynamical diffraction effects and slight crystal misorientations.