Large area strain analysis using scanning transmission electron microscopy across multiple images

Abstract

Here, we apply revolving scanning transmission electron microscopy to measure lattice strain across a sample using a single reference area. To do so, we remove image distortion introduced by sample drift, which usually restricts strain analysis to a single image. Overcoming this challenge, we show that it is possible to use strain reference areas elsewhere in the sample, thereby enabling reliable strain mapping across large areas. As a prototypical example, we determine the strain present within the microstructure of a Ni-based superalloy directly from atom column positions as well as geometric phase analysis. While maintaining atomic resolution, we quantify strain within nanoscale regions and demonstrate that large, unit-cell level strain fluctuations are present within the intermetallic phase.

Atom site preference and γ′/γ mismatch strain in Ni Al Co Ti superalloys

“…The observed strain gradient originates from lattice distortion within the alloy due to coherency strain introduced by thermal expansion mismatch between the phases. This behavior is consistent with prior investigations with other techniques characterising γ/γ interfaces in superalloys [3,21,22,26,35]. Beyond strain, lattice misfit, δ, between the γ and γ phases is another important descriptor of superalloy system, defined as:…”

“…[3] is closer to the true unconstrained lattice misfit [21]. Furthermore, strain relaxation in the TEM specimen due to the presence of free surfaces can contribute to the partial relaxation of coherency strain [21,22,26]. In addition, the average sample region for RevSTEM analysis is smaller (∼25 nm 2 ) in comparison to the larger sample area (∼mm 2 ) for neutron diffraction.…”

“…In contrast, the recent introduction of revolving scanning transmis-2 sion electron microscopy (RevSTEM) enables accurate and precise measurement directly in real space at the atomic scale [24,25]. Furthermore, this technique has been shown to provide direct nanoscale strain in a ternary superalloy containing Ni, Al, and Cr and offers new opportunities to explore this class of materials [26].…”

Strain mapping at nanometer resolution using advanced nano-beam electron diffraction

“…However, recently it was shown that the use of multiple images and correction of the drift and scan distortions can increase the achievable FOV for HRSTEM. 16 Dark-field electron holography (DFEH) techniques, either off-axis 17 or in-line, 18 provide a larger FOV reaching up to 1 lm but require a dedicated microscope equipped with an electrostatic bi-prism or a sophisticated focal series reconstruction algorithm, respectively. In addition, both HRSTEM and holographic techniques require the sample to be in exact zone axis or two-beam diffracting condition and to have exactly the same orientation throughout the entire analyzed area.…”

Oxygen vacancy ordering induced displacements of cations in yttria-stabilized zirconia

“…[3][4][5][6] Using aberration corrected STEM, the lattice distortions in materials can now be measured on a unit-cell by a unit-cell basis and at the picometer level. [7][8][9] The clear view of atom positions enables direct comparison of experiment with theory modeling. 7,8,[10][11][12] In this work, we employ the contrast based on the high-angle scattering of electrons (Z-contrast) in a STEM mode to image the cation sub-lattice only, which allows for directly measuring vacancy-induced displacements of cations in YSZ.…”