Evaluation of alternative scan strategies for high resolution STEM imaging

Date: 7 February 2020

Venue: UAntwerp, Campus Groenenborger, Room U.408 - Groenenborgerlaan 171 - 2020 Antwerp (Wilrijk) (route: UAntwerpen, Campus Groenenborger)

Time: 11:30 AM - 12:15 PM

Organization / co-organization: EMAT

Short description: Friday Lecture by Abner Velazco Torrejón, EMAT

About the lecture

Scanning transmission electron microscopes (STEMs) equipped with spherical aberration correctors are well known for their ability to obtain images with atomic scale information. This is achieved by raster scanning a focused electron probe over a sample at sub-Angstrom resolution. At such high resolution, typically small field of views on the order of hundreds of nm2 are irradiated/imaged and among others two main difficulties arise: fast degradation of beam sensitive materials, and image distortions predominantly in the so called ‘slow scan direction’ because of drift of the sample/stage.

Here we present the evaluation of alternative scan strategies to mitigate these difficulties. In the first part of my talk, I will present results of damage reduction on a beam sensitive sample (commercial LTA Zeolite) by changing the temporal distribution of the dose, while maintaining the same total dose and dose rate as in conventional raster scanning. The second part will show how a more isotropic rectangular scan strategy, which changes the direction of the scanning every one or two steps, can more faithfully represent the high frequency content of the images in the presence of drift. Moreover, it provides reduced bias when measuring lattice parameters while maintaining similar precision in both scan directions. This scan strategy does not require the so called ‘flyback’ motion of the raster scanning, eliminating the need of delays for stabilization of the probe after this abrupt jump. Hence, this scan strategy requires less dose and acquisition time compared to the raster scanning method.

Link: https://www.uantwerpen.be/en/research-groups/emat/