Insights into Sintering of Metallic Nanoparticles Using Molecular Dynamics Simulations: Implications for Additive Nanomanufacturing

Abstract

Additive nanomanufacturing, which utilizes laser-induced nanoparticle (NP) ablation and sintering, offers a versatile approach for fabricating novel electronic devices with unique properties. This technique allows for tunable composition and porosity state of the sintered material, as well as compatibility with various substrates, including biodegradable ones. However, achieving desired sintering without damaging the substrate requires careful control of laser energy input and duration. The porosity state of the sintered material, which determines its properties such as the electronic circuit resistivity, depends not only on temperature (determined by laser energy input) but also on NP size, size ratio, crystallographic misorientation, material type, and miscibility. To gain a quantitative understanding of these dependencies, this dissertation work employs molecular dynamics simulations to investigate the sintering behavior of monometallic NP doublets (silver and copper) and bimetallic NP doublets (silver-copper and silver-gold) at varying temperatures. It analyzes the influence of NP size, size ratios, misorientation angles (tilt and twist), material type (comparing silver and copper), and miscibility (comparing silver-copper and silver-gold) on the sintering outcomes. Based on the results, a mathematical framework to describe the characteristic sintering time; the time required for monometallic/bimetallic NP doublets to reach specific normalized neck sizes has been proposed. Additionally, the formation and evolution of crystallographic defects (vacancies, dislocations, stacking faults, twin boundaries, and grain boundaries) during sintering are explored to elucidate the underlying sintering mechanisms, such as crystallographic defect-mediated and surface-mediated diffusion processes. Keywords: Additive nanomanufacturing; Sintering; Nanoparticles; Molecular dynamics; Crystallographic defects