On Self-Limiting Rotation and Diffusion Mechanisms during Sintering of Silver Nanowires

Abstract

Understanding the mechanisms and kinetics of thermal sintering between silver nanowires (NWs) is critical for multiple emerging applications. We use molecular dynamics simulations to reveal the kinetics and mechanisms of sintering between stacked silver NW pairs with nonparallel axes, which realistically mimics geometric configurations in experimentally relevant NW networks. Relative NW orientation has a hitherto-unknown but significant and nonlinear influence on inter-NW neck growth. This is due to a dynamic interaction between surprisingly high rigid-body rotation of the NWs, atomic diffusion, and dislocation generation that demarcates diffusion-dominated and dislocation-dominated regimes of neck growth. Thus, the current assumption that the relative orientation of NWs has a purely geometric and quasi-static effect on NW sintering is incomplete. Our findings also stress the need to consider the effect of large local rotations and the consequently large spatial gradients in neck growth on sintering-driven properties (e.g., electrical) of NW networks, yielding new knowledge that will play a key role in the rational design and processing of NW networks.

Multiscale Modeling of Sintering-Driven Conductivity in Large Nanowire Ensembles

“…This model assumes that the change in ensemble resistivity during sintering is solely due to inter-NW neck growth. It also incorporates the following mechanistic insights from our past MD simulations of isothermal sintering between Ag NW pairs . First, the neck boundary is modeled as a 3D curve, as shown in Figure f.…”

“…Second, because of NW rotation, the diffusion coefficients corresponding to neck growth and the virtual torque corresponding to NW rotation are functions of the NW radius R , instantaneous orientation angle θ, and the sintering temperature T . Readers are referred to this past work for further details of MD simulations …”

“…Conductivity models for as-printed ensembles do not explicitly consider sintering-driven neck growth. − Phenomenological models that explicitly consider neck growth have modeled the ensemble conductivity as a function of the instantaneous temperature. ,, This ignores the fact that the temperature history and not just the instantaneous temperature drive neck growth, especially under nonisothermal sintering conditions. , As-printed NW ensembles typically consist of multiple layers of stacked NWs with junction-to-junction variations in the relative NW orientation (Figure a–d). Recent molecular dynamics (MD) simulations have shown significant local rotation of the NWs during sintering, which tends to align the NWs to reduce the total surface energy (Figure e) . The amount of this rotation depends on the NW radius and the junction-specific value of the initial orientation angle θ (Figure f).…”

“…(e) Snapshots of NW rotation during sintering from MD simulations. Reproduced with permission from reference . Copyright 2020 American Chemical Society.…”

Phase-field study of surface diffusion enhanced break-ups of nanowire junctions

“…Phase-field modelling has been used previously to simulate the sintering of Ag nanoparticles [67]. The effect of local sintering at the junction of nanowires have also been studied using atomistic simulation methods, where it was observed that the nanowires undergo self-limiting rotation during neck growth, which is a result of complex interaction of surface diffusion and dislocation growth [68]. We also observe the nanowire junction break-up in all cases described above as a result of local sintering at the junctions of nanowires.…”