Bragg coherent diffraction imaging of iron diffusion into gold nanocrystals

Abstract

Understanding how diffusion takes place within nanocrystals is of great importance for their stability and for controlling their synthesis. In this study, we used the strain sensitivity of Bragg coherent diffraction imaging (BCDI) to study the diffusion of iron into individual gold nanocrystals in situ at elevated temperatures. The BCDI experiments were performed at the I-07 beamline at Diamond Light Source, UK. The diffraction pattern of individual gold nanocrystals was measured around the (11-1) Bragg peak of gold before and after iron deposition as a function of temperature and time. Phase retrieval algorithms were used to obtain real space reconstructions of the nanocrystals from their measured diffraction patterns. Alloying of iron with gold at sample temperatures of 300°C-500°C and dealloying of iron from gold at 600°C were observed. The volume of the alloyed region in the nanocrystals was found to increase with the dose of iron. However, no significant time dependence was observed for the structure following each iron deposition, suggesting that the samples reached equilibrium relatively quickly. The resulting phase distribution within the gold nanocrystals after the iron depositions suggests a contraction due to diffusion of iron. Our results show that BCDI is a useful technique for studying diffusion in three dimensions and alloying behaviour in individual crystalline grains.

Mapping data between sample and detector conjugated spaces in Bragg coherent diffraction imaging

“…where V LS is the volume created by x, y, z and N 1 , N 2 , N 3 , which corresponds to the number of steps or pixels in the data array (Estandarte et al, 2018). Based on equation (7), normalizing q x , q y and q z would give the LS unit vectorŝ x x,ŷ y andẑ z, respectively.…”

“…As a guide, p sam x;y;z ¼ D dN 1;2 ; where is the X-ray wavelength, D is the detector distance, d is the detector pixel size and N 1 and N 2 correspond to the number of steps or pixels in the data array in LS and RLS(Estandarte et al, 2018).…”

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

“…Previously, BCDI has been used to investigate annealing of 3C-SiC nanoparticles (Hruszkewycz et al, 2018), diamond nanoparticles (Hruszkewycz et al, 2017), magnetite crystals (Yuan et al, 2019) and metallic glass (Chen et al, 2020). Furthermore, BCDI has been extensively used to study Au subject to iron diffusion (Estandarte et al, 2018), copper diffusion (Xiong et al, 2015) and catalytic oxidation (Suzana et al, 2019). However, these experiments only considered one reflection, and thus only the strain along the Bragg vector could be resolved.…”

Structure of a single palladium nanoparticle and its dynamics during the hydride phase transformation

“…The amplitude of the resulting 3D complex image is proportional to the electron density of the crystal contributing to the Bragg peak and the phase is proportional to the displacement field of the crystalline structure compared with the equilibrium position of their atoms 13 . The technique can reach nanometric real space resolution, usually 10-20 nm 14 , while the distortions caused by strain are given with subangstrom sensitivity 13 . The possibility of using reactive environments during the measurement makes BCDI an ideal technique to probe dynamic changes and observe the evolution of defects' distribution.…”