Dealloying in Individual Nanoparticles and Thin Film Grains: A Bragg Coherent Diffractive Imaging Study

Abstract

Dealloying is a process whereby selective dissolution results in a porous, strained structure often with new properties. The process is of both intrinsic and applied interest, and recently has been used to make highly active catalysts. The porosity has been studied using electron microscopy while the dealloying-induced strain has been studied at the ensemble level using X-ray diffraction. Despite the importance of local, for example, at the individual particle or grain level, strain in controlling the properties of the dealloyed material, it remains unresolved due to the difficulty of imaging 3D strain distributions with nanometer resolution in reactive environments. This information could play an integral role in understanding and controlling lattice strain for a variety of applications. Here, 3D strain distributions in individual nanoparticles and thin film grains in silver-gold alloys undergoing nitric acid-induced dealloying are imaged by Bragg coherent diffractive imaging. Particles exhibit dramatic changes in their local strains due to dealloying but grains do not. The average lattice in both grains and particles contracts during dealloying. In general, the results reveal significant dealloying-induced strain heterogeneity at the nanoscale in both isolated and extended samples, which may be utilized to develop advanced nanostructures for a variety of important applications.

Study of the Internal Compositions of Binary Alloy Pd-Rh Nanoparticles by Using Bragg Coherent Diffraction Imaging

“…Under the assumption, we define the compositional strain, like the elastic strain [16], as the longitudinal component of the gradient of the displacement field, u111(r) as…”

In situ Bragg coherent X-ray diffraction imaging of corrosion in a Co–Fe alloy microcrystal

“…A binary alloy was chosen for this study to identify how strain distributions can be affected by the presence of another element during corrosion. 23,24 BCDI allows 3D-resolved, nanoscale strain measurements with a 3D spatial resolution of 10–30 nm and a strain resolution on the order of ∼2 × 10 –4 , 25 making it well suited to probing crystal defects and morphology. Currently, at third generation synchrotron light sources, several minutes are required to collect a BCDI dataset.…”

Angle calculations using two detector circles and wavelength

“…In recent years, nanoparticle crystals or nanograins have been widely studied using X-ray beams tightly focused to maximize diffraction intensity, for example, in coherent diffraction imaging (Cha et al, 2017;Liu et al, 2017;Ulvestad et al, 2017) and Bragg ptychography (Hruszkewycz et al, 2013). In these cases, the beam sizes are typically close to or less than a micrometre.…”