Session: 16-01-01: Poster Session: NSF-Funded Research (Grad & Undergrad)

Paper Number: 99561

99561 - Full-Field Deformation Measurement in the Transmission Electron Microscope Using in Situ Digital Image Correlation and Particle Tracking 

Measuring displacement and/or strain fields at the nanoscale during material deformation can be essential in developing a multiscale understanding of material response. As a popular non-contact optical method developed in 1980s, digital image correlation (DIC) has been widely applied for characterization of macroscale material response. More recently, it has also been extended to mesoscale studies under optical microscopes and microscale studies using scanning tunneling microscopy (STM), atomic force microscopy (AFM) and scanning electron microscopy (SEM). In addition to these, transmission electron microscopy (TEM) can directly image dislocation motion, slip bands, and shear bands potentially providing the ability to pair qualitative imaging results with quantitative DIC measurements. In this work, we develop an experimental approach where digital image correlation (DIC) and particle tracking (PT) are both applied for characterizing in situ microscale deformation in the TEM. We use the 1 µm thick thermally grown amorphous SiO₂ as a demonstrative material of this experimental process. Gold nanoparticles deposited on SiO₂ provide both the speckle patterns required by DIC when averaged over a subset region, and target particles for PT. To demonstrate and validate the feasibility of using DIC in the TEM, micron sized SiO₂ beam samples with built-in ends on both sides are machined using focused ion beam (FIB) milling and loaded in the TEM via diamond punch indentation using Bruker PI95 PicoIndenter. DIC and PT are then applied to measure in situ displacements from a sequence of TEM images taken during loading of the beam. Noise levels introduced by TEM image drifting are investigated by baseline tests without loading and deformation in different TEMs. Deformation results of the two measurement methods in the loading experiment agree well with each other, thus demonstrating effectiveness in determining local displacements from TEM experiments using both methods. Compared to the displacement measurements at the loading point from the PicoIndenter, DIC/PT results show a better consistency between experiments with the same geometry and loading configuration, which again proves the reliability of DIC/PT measurements. As an application of TEM full-field measurement, we study the creep behavior of amorphous SiO₂ induced by electron beam irradiation. Ramp-steps loading profile is used to trigger creep responses at different load levels. Using DIC creep deformation results from TEM images, creep properties are extracted and validated in a 2D finite element model. Error sources and discrepencies especially at higher load levels related to 3D out-of-plane effect are also discussed.

Presenting Author: Yiguang Zhang University of Illinois at Urbana-Champaign

Presenting Author Biography: I graduated from the undergraduate school in Harbin Institute of Technology in 2018. Now I'm a 4th year PhD student in aerospace engineering department of University of Illinois at Urbana-Champaign. My research interest is in-situ microscale mechanical behavior of glass and ceramic materials in the transmission electron microscope.

Authors:

Yiguang Zhang University of Illinois at Urbana-Champaign
Shen Dillon University of California Irvine
John Lambros University of Illinois at Urbana-Champaign