Coherent Diffraction imaging at sub-angstrom resolution in a Transmission electron microscope

Here we describe a new TEM-based coherent diffraction imaging (CDI) method to achieve sub-ångström resolution in lattice images of nanoparticles. The experiments were performed by using a TEM/STEM JEOL 2010F UHR (objective lens spherical aberration coefficient of (0.47±0.01) mm) with resolution at optimum defocus of 0.19nm and equipped by Schottky cathode. The experiments for CDI require the acquisition of HRTEM image and diffraction from the same region of the sample illuminated by a coherent electron probe. The experimental nano-diffraction must be recorded with the beam coherence length larger than the region to be imaged according to the oversampling requirements [1]. A new efficient iterative phase retrieval algorithm [2] based on pioneering work of Gerchberg and Saxton [3] has been developed and successfully applied. Figure 1 is an example of phase retrieval of a TiO2 particle at a resolution of 70 pm that allows to distinguish the O atoms appreciating subtle alterations in the unit cell structure of the nano-crystals, which would not be otherwise detectable by conventional HRTEM. Such structural deviations could be at the origin of peculiar size-dependent physical-chemical properties of the concerned oxide material in the nanoscale regime [2].