Robust Strain Mapping at Subnanometer Resolution & Subpicometer Precision
Published December 22, 2020
E. Padgett, M. E. Holtz, P. Cueva, Y.-T. Shao, E. Langenberg, D. G. Schlom, and D. A. Muller
Four-dimensional scanning transmission electron microscopy (4D-STEM) technique along with an electron microscope pixelated array detector (EMPAD) enables spatially resolved mapping of crystal structure with length scales ranging from sub-Angstrom to over micrometers. 4D-STEM works by recording full electron diffraction patterns at each probe position in real-space, which offers a unique opportunity to extract quantitative structural information such as strain, electric and magnetic fields at sub-nm resolution. However, dynamical diffraction effects and specimen mistilts impose challenges for measuring the shifts in Bragg reflections for strain analysis. Here, we present the EWPC (exit-wave power cepstrum) transform approach for robust strain mapping at sub-nm resolution and sub-pm precision. Inspired by cepstral analysis in audio signal processing, EWPC decouples the strain information from crystal mistilts and thickness variation artefacts. It provides a mapping to a good basis for performing machine learning of structure-property relationships, without being dominated by imaging artifacts that have plagued previous approaches.