Annealing of focused ion beam damage in gold microcrystals: an in situ Bragg coherent X-ray diffraction imaging study

Abstract

Focused ion beam (FIB) techniques are commonly used to machine, analyse and image materials at the micro- and nanoscale. However, FIB modifies the integrity of the sample by creating defects that cause lattice distortions. Methods have been developed to reduce FIB-induced strain; however, these protocols need to be evaluated for their effectiveness. Here, non-destructive Bragg coherent X-ray diffraction imaging is used to study the in situ annealing of FIB-milled gold microcrystals. Two non-collinear reflections are simultaneously measured for two different crystals during a single annealing cycle, demonstrating the ability to reliably track the location of multiple Bragg peaks during thermal annealing. The thermal lattice expansion of each crystal is used to calculate the local temperature. This is compared with thermocouple readings, which are shown to be substantially affected by thermal resistance. To evaluate the annealing process, each reflection is analysed by considering facet area evolution, cross-correlation maps of the displacement field and binarized morphology, and average strain plots. The crystal's strain and morphology evolve with increasing temperature, which is likely to be caused by the diffusion of gallium in gold below ∼280°C and the self-diffusion of gold above ∼280°C. The majority of FIB-induced strains are removed by 380–410°C, depending on which reflection is being considered. These observations highlight the importance of measuring multiple reflections to unambiguously interpret material behaviour.

Refinements for Bragg coherent X-ray diffraction imaging: Electron backscatter diffraction alignment and strain field computation

“…6 shows the strain and rotation tensors reconstructed from five measured Bragg reflections of crystal 1B. The xx , yy , and zz slices show defects close to the edge that may not be resolved if analysing a single reflection alone (Yang et al, 2021) as some crystal defects, such as dislocations, are visible only when Q hkl •b = 0, where b is the Burgers vector (Williams & Carter, 2009).…”

“…Since the development of BCDI in the early 2000's, most experiments feature the measurement of a single reflection, providing only one component of the strain tensor. However, the analysis of a single strain component can be ambiguous as different information is obtained for different reflections (Yang et al, 2021). If at least three linearly independent reflections are measured, the full 3D strain tensor can be calculated.…”

Bragg Coherent Diffraction Imaging for In Situ Studies in Electrocatalysis

“…BCDI has been applied in several fields of science and technology including the study of NPs in general, ,,,,,− zeolites, , heterogeneous catalysis, ,,− batteries, − supercapacitors dielectrics, − nanowires, ,− minerals, − alloys and dealloying, − nanorods, ,− proteins, − thin films, ,…”

Three-Dimensional In-Situ Imaging of Single-Grain Growth in Polycrystalline Films

“…Lensless Bragg coherent X-ray diffraction imaging (BCDI) addresses above-mentioned limitations by providing high-resolution 3D structure and strain in single nanoparticles under realistic conditions [14]. In-situ 3D imaging of annealing processes, defects formation, and phase transformations in grains and nanoparticles was demonstrated in a number of recent works [15][16][17]. The 3D diffraction patterns arising by coherent X-ray scattering from an isolated crystalline grain are highly sensitive to the shape and strain (down to 10 −4 ) [18,19].…”