Date of Award
12-2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Mechanical Engineering
Committee Chair/Advisor
Dr. Huijuan Zhao
Committee Member
Dr.Hongseok Choi
Committee Member
Dr. Gang Li
Committee Member
Dr. Xin Zhao
Abstract
Gold nanoparticles (AuNPs) offer exciting possibilities due to their inertness, malleability, and tunable structures, making them valuable for applications ranging from nanomedicine to electronics. Their optical, mechanical, and other properties can be tailored by modifying shape and structure, underscoring the importance of understanding their deformation behaviour at the nanoscale. This study used classical molecular dynamics simulations with LAMMPS to investigate the deformation mechanisms of gold nanospheres (AuNS) under uniaxial compression. Employing the embedded atom method (EAM) potential to model atomic interactions, AuNS with 20 nm in diameter were compressed along the z-direction using planar indenters moving at a constant velocity. True stress was calculated based on the contact surface area and the force applied. The contact surface acted as a dislocation source, while the outer surface functioned as a dislocation sink. Comparative analysis across orientations revealed that compressing the AuNS in [111] direction exhibited higher yield stress than that in [110] and [001] oriented AuNS. Deformation mechanisms varied with respect to the orientation of AuNS. At strains above 15%, [001]-oriented AuNS displayed multiple deformation behaviours independent of temperature, strain rate, or size. We applied unsupervised machine learning to categorize deformation mechanisms based on stress, strain and dislocation density. The analysis identified three distinct deformation mechanisms in [001]-oriented AuNS: dislocation exhaustion, dislocation starvation, and dislocation multiplication. Dislocation exhaustion involves the escape of dislocations through the outer surface, resulting in strain-hardening. Dislocation starvation was characterized by a balance between dislocation nucleation and annihilation rates, while dislocation multiplication involved rapid dislocation accumulation within the AuNS. Previous studies on gold nanorods reported hardening driven by dislocation starvation behavior. However, a comparative analysis of [001]-oriented gold nanospheres and nanorods highlighted significant differences in their deformation mechanisms and the emergence of dislocation multiplication in gold nanorods. These findings provide valuable insights into the deformation behaviour of AuNPs, advancing the design of nanoscale materials with tailored properties.
Recommended Citation
Gupta, Tanuj, "Deformation Mechanism in Gold Nanoparticles Under Compressive Loading: Insights From Atomistic Modelling and Unsupervised Machine Learning" (2024). All Dissertations. 3777.
https://open.clemson.edu/all_dissertations/3777
