Importance of TEM sample thickness for measuring strain fields

Sangjun Kang; Di Wang; Christian Kübel; Xiaoke Mu

doi:10.1016/j.ultramic.2023.113844

Importance of TEM sample thickness for measuring strain fields

Ultramicroscopy. 2024 Jan:255:113844. doi: 10.1016/j.ultramic.2023.113844. Epub 2023 Sep 2.

Authors

Sangjun Kang¹, Di Wang², Christian Kübel³, Xiaoke Mu⁴

Affiliations

¹ Institute of Nanotechnology (INT), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen 76344, Germany; Joint Research Laboratory Nanomaterials, Technical University of Darmstadt (TUDa), Darmstadt 64287, Germany. Electronic address: sangjun.king@outlook.com.
² Institute of Nanotechnology (INT), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen 76344, Germany; Karlsruhe Nano Micro Facility (KNMFi), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen 76344, Germany.
³ Institute of Nanotechnology (INT), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen 76344, Germany; Joint Research Laboratory Nanomaterials, Technical University of Darmstadt (TUDa), Darmstadt 64287, Germany; Karlsruhe Nano Micro Facility (KNMFi), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen 76344, Germany. Electronic address: christian.kuebel@kit.edu.
⁴ Institute of Nanotechnology (INT), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen 76344, Germany. Electronic address: muxiaoke@gmail.com.

PMID: 37708815
DOI: 10.1016/j.ultramic.2023.113844

Abstract

Transmission electron microscopy (TEM) has emerged as a valuable tool for assessing and mapping strain fields within materials. By directly analyzing local atomic spacing variations, TEM enables the precise measurement of local strain with high spatial resolution. However, it is standard practice to use thin specimens in TEM analysis to ensure electron transparency and minimize issues such as projection artifacts and contributions from multiple scattering. This raises an important question regarding the extent of structural modification, such as strain relaxation, induced in thin samples due to the increased surface-to-volume ratio and the thinning process. In this study, we conducted a systematic investigation to quantify the influence of TEM sample thickness on the residual strain field using deformed Fe-based and Zr-based metallic glasses as model systems. The samples were gradually thinned from 300 nm to 70 nm, and the same area was examined using 4D-STEM with identical imaging settings. Our results demonstrate that thinning the sample affects the atomic configuration at both the short-range (SR) and medium-range (MR) scales. Consequently, when the sample is thinned too much, it no longer preserves the native deformation structure. These findings highlight the critical importance of maintaining sufficient TEM sample thickness for obtaining meaningful and accurate strain measurements.

Keywords: 4D-STEM; FIB damage; Sample thickness; Strain mapping; Strain relaxation.