CE08 - Matériaux métalliques et inorganiques et procédés associés

Defects in Nanocrystals: Coherent Diffraction Imaging and Simulations – DINACS

Submission summary

Defects in crystals whether they are 2D (grain boundaries, stacking faults …), 1D (dislocations), or 0D (point defects) have a critical influence on the properties of bulk solids. At the nanoscale a single defect can completely modify the properties of a nanocrystal. Moreover, because of the close proximity of surfaces the energy and mobility of defects in single nano-objects are borne to be very different from what they are in the bulk. It has been recognized that crystal defects of various nature and length scales are not always adverse but can instead give rise to specific functionalities, such as improving adsorption affinity or catalytic activity. This project is aimed at an in-depth investigation of defects in metallic nanoparticles as well as their behavior under mechanical loading and their influence on catalytic activity. We propose using Bragg Coherent Diffraction Imaging (BCDI) which has become the most effective technique for imaging the 3D structure of individual crystals at the nanometer scale with an unmatched sensitivity to displacement fields. Thanks to the high brilliance, coherence and flux of the 3rd (and now 4th) generation synchrotron x-ray beams, BCDI has shown its capability to image single defects in nano-crystals together with a picometer resolution on the displacement field. One of the novelties of the project is the massive use of BCDI which offers nowadays a unique and revolutionary tool to image defects and strain field in 3 dimensions.
To investigate the defects stability, three in-situ experiments combining mechanical test and x-ray measurements will be employed:
- a nanoindentation test performed in-situ with an atomic force microscope (AFM), that has been developed at IM2NP and has already successfully been used in combination with BCDI and Laue microdiffraction at different beamlines.
- a diamond anvil cell compatible with coherent diffraction measurements which allows applying either hydrostatic or non-hydrostatic stress.
- a furnace to apply thermoelastic strain thanks to the difference between the coefficients of thermal expansion of the substrate and the nanoparticles.
In addition, atomic scale simulations will be performed to gain access to the defects configurations and strain field at the atomic scale. It will greatly help in understanding the observed defects stability and behaviors during mechanical test of the nanoparticles. Typical sizes of a few tens of nanometers, comparable to the experimental ones, will be considered. Reliable interatomic potentials, based on the embedded-atom method, will be used to model the chosen metals.
In a second stage, Molecular Dynamics (MD) and Discrete Dislocation Dynamics (DDD) simulations will allow following the defects behavior inside the nanoparticles under mechanical load. On the one hand with MD simulations, the movement of the pre-existing defects, their interactions, their possible annihilation at surfaces, and the possible nucleation of new defects can be examined at a fine length and time scale. On the other hand, in large nanoparticles, where MD computational cost becomes demanding, DDD mesoscale simulations will be used, integrating the mechanism observed in MD simulations. DDD coupled with a finite element (FE) solver, is an effective tool to study the plastic behavior of nanoparticles. Both MD and DDD results will finally be compared to the in-situ BCDI experimental observations.
As a final step, the influence of extended defects (dislocations, stacking faults, twins) inside single metallic nano-objects will be monitored in situ and operando during catalytic reactions using BCDI.
The originality of this project is based on in-situ 3D imaging of defects stability in nano-objects combined with atomic and mesoscale simulations.

Project coordination

Stéphane Labat (Institut des Matériaux, de Microélectronique et des Nanosciences de Provence)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Pprime Institut P' : Recherche et Ingénierie en Matériaux, Mécanique et Energétique
LEM Laboratoire d'étude des microstructures
Technion-Israel Institute of Technology / Departement of matérials Science and Engineering
SOLEIL Synchrotron SOLEIL
IM2NP Institut des Matériaux, de Microélectronique et des Nanosciences de Provence
MEM Modélisation et Exploration des Matériaux

Help of the ANR 469,962 euros
Beginning and duration of the scientific project: - 42 Months

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