Reference : UMR104-RICGAT-001
Nombre de Postes : 1
Workplace : CHATILLON
Date of publication : Monday, January 16, 2023
Type of Contract : FTC Scientist
Contract Period : 16 months
Expected date of employment : 1 March 2023
Proportion of work : Full time
Remuneration : From 2889,51 euros gross per month depending on experience
Desired level of education : PhD
Experience required : 1 to 4 years
Defects in crystals, whether 2D (grain boundaries, stacking defects, etc.), 1D (dislocations) or 0D (point defects), have a crucial influence on the properties of bulk materials. At the nanoscale, a single defect can completely change the properties of a nanocrystal. Crystal defects are not only relevant for the mechanical behaviour. Indeed, it has been shown that crystal defects of different natures and length scales are not always detrimental, but can instead give rise to specific functionalities, such as enhanced catalytic activity. For example, stacking faults improve the catalytic efficiency of nanoparticles and more generally the deformation generated by defects can affect the catalytic activity. This defect sensitivity could open new ways for engineering the properties of nanostructures by introducing specific defects. To this end, the main objective is to understand the behaviour of defects (nucleation, motion, annihilation, defect-defect interaction) including the deformation fields surrounding them, in nano-objects subjected to external loading.
In a first step, atomic scale simulations of nanoparticles will be performed to gain access to the defect configurations and the atomic scale deformation field. The stability of pre-existing defects in the nanoparticles will be tested and compared with experimental measurements obtained at IM2NP with Bragg coherent diffraction imaging (BCDI).
In a second step, molecular dynamics (MD) and discrete dislocation dynamics (DDD) simulations will be used to investigate the behaviour of defects inside nanoparticles under mechanical loading. On the one hand, MD simulations will allow us to examine the movement of initial defects, their possible annihilation at the surface, their interactions and the nucleation of new defects on a very small time and length scale. On the other hand, in large nanoparticles, where the MD computational cost becomes demanding, mesoscale DDD simulations will be used, integrating the mechanism observed in the MD simulations. As shown in the literature, DDD coupled with a finite element (FE) solver is an efficient tool to study the plastic behaviour of nanoparticles. The results of the MD and DDD simulations will finally be compared to the in-situ experimental observations of the BCDI.
Through the comparison between simulations and experiments, this post-doctoral project aims to better understand the link between pre-existing defects and mechanical properties of nanoparticles.
-Acquiring the different techniques for simulating plasticity at the atomic (MD) and mesoscopic (DDD and EF) scales.
-Study of the stability of linear defects in nanoparticles.
-Simulation of the mechanical properties of nanoparticles.
-Comparison with mechanical testing and Bragg coherent diffraction imaging measurements.
Good knowledge of condensed matter physics and a strong background in numerical simulation (use of simulation softwares, coding for post-processing of data).
The Postdoc project will be realised at the Laboratory of Microstructure Studies (LEM). The LEM is a joint CNRS-ONERA research unit, bringing together permanent staff from ONERA, CNRS and the University. The research carried out is mainly aimed at studying the microstructures developing in materials as well as the modelling and characterisation of low-dimensional systems.
This research work is part of the ANR DINACS project which aims to study the defects present in metallic nanoparticles, as well as their behaviour under mechanical load and their influence on catalytic activity.
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