Real-space tilting method for atomic resolution STEM imaging of nanocrystalline materials

TL;DR

This paper introduces a real-space tilting method for atomic-resolution STEM imaging of nanocrystalline materials that does not require diffraction pattern analysis, enabling automated, low-dose imaging of beam-sensitive samples.

Contribution

A novel real-space tilting technique based on shadow image contrast change that accurately aligns nanocrystalline samples without prior knowledge or diffraction patterns.

Findings

Corrects misorientation angles > ±6.9° with sub-mrad accuracy

Enables automatic tilting to the zone axis under low dose conditions

Facilitates atomic-scale characterization of beam-sensitive nanomaterials

Abstract

Atomic-resolution scanning transmission electron microscopy (STEM) characterization requires precise tilting of the specimen to high symmetric zone axis, which is usually processed in reciprocal space by following the diffraction patterns. However, for small-sized nanocrystalline materials, their diffraction patterns are too faint to guide the tilting process. Here, a simple and effective tilting method is developed based on the diffraction contrast change of the shadow image in the Ronchigram. We can calculate the misorientation angle of the specimen and tilt it to the zone axis based on the position of the shadow image with lowest intensity. This method requires no prior knowledge of the sample and the maximum misorientation angle we can correct is greater than +-6.9 degree with sub-mrad accuracy. It is processed in real space, without recording the diffraction patterns of the specimens, which can effectively apply to nanocrystalline materials. Combined with the scripting to control the microscope, we can automatically tilt the sample to the zone axis under low dose condition (<0.17 e-/A2/s), which could facilitate the imaging of beam sensitive materials such as zeolites or metal organic frameworks. This automated tilting method could contribute to the atomic-scale characterization of the nanocrystalline materials by STEM imaging.