In Situ Nano-Indentation of a Gold Sub-Micrometric Particle Imaged by Multi-Wavelength Bragg Coherent X-ray Diffraction

Abstract

The microstructure of a sub-micrometric gold crystal during nanoindentation is visualized by in situ multi-wavelength Bragg coherent X-ray diffraction imaging. The gold crystal is indented using a custom-built atomic force microscope. A band of deformation attributed to a shear band oriented along the (221) lattice plane is nucleated at the lower left corner of the crystal and propagates towards the crystal center with increasing applied mechanical load. After complete unloading, an almost strain-free and defect-free crystal is left behind, demonstrating a pseudo-elastic behavior that can only be studied by in situ imaging while it is invisible to ex situ examinations. The recovery is probably associated with reversible dislocations nucleation/annihilation at the side surface of the particle and at the particle-substrate interface, a behavior that has been predicted by atomistic simulations. The full recovery of the particle upon unloading sheds new light on extraordinary mechanical properties of metal nanoparticles obtained by solid-state dewetting.

Capturing Catalyst Strain Dynamics during Operando CO Oxidation

“…21,22 However, BCDI has been challenging to realize with meaningful time resolution during in situ catalysis, where improvements have generally been accompanied by a reduction in oversampling 23 or dimensionality. 24,25 Furthermore, single-shot pump−probe measurements 26 generally require a large population of near-identical particles 20 which is not suitable to probe strain localized to NP surfaces and vertices. Instead, charge-integrating detectors which maximize the dynamic range while reducing X-ray exposure are best suited to improve temporal resolution.…”

“…This is due to the retrieval of the phase which encodes the local deformations of the crystal lattice . During pump–probe (laser-excited) BCDI experiments, it has been possible to resolve 3D lattice dynamics in nanocrystals at femto- and pico-second time scales. , However, BCDI has been challenging to realize with meaningful time resolution during in situ catalysis, where improvements have generally been accompanied by a reduction in oversampling or dimensionality. , Furthermore, single-shot pump–probe measurements generally require a large population of near-identical particles which is not suitable to probe strain localized to NP surfaces and vertices. Instead, charge-integrating detectors which maximize the dynamic range while reducing X-ray exposure are best suited to improve temporal resolution …”