Self-assembly of a drop pattern from a two-dimensional grid of nanometric metallic filaments

TL;DR

This paper investigates the self-assembly of metallic drop patterns from nanometric nickel filament grids on a substrate, combining experiments, fluid mechanical modeling, and numerical simulations to predict final drop configurations based on initial geometry.

Contribution

It introduces a fluid mechanical model that predicts the number of resulting drops from a nanometric metallic grid, validated by experiments and numerical simulations.

Findings

Good agreement between model predictions and experimental data.

Identification of aspect ratio intervals for specific drop counts.

Numerical simulations effectively describe the dynamics of filament breakup.

Abstract

We report experiments, modeling and numerical simulations of the self--assembly of particle patterns obtained from a nanometric metallic square grid. Initially, nickel filaments of rectangular cross section are patterned on a SiO$_2$ flat surface, and then they are melted by laser irradiation with $\sim 20$ ns pulses. During this time, the liquefied metal dewets the substrate, leading to a linear array of drops along each side of the squares. The experimental data provides a series of SEM images of the resultant morphology as a function of the number of laser pulses or cumulative liquid lifetime. These data are analyzed in terms of fluid mechanical models that account for mass conservation and consider flow evolution with the aim to predict the final number of drops resulting from each side of the square. The aspect ratio, $\delta$, between the square sides' lengths and their widths is an essential parameter of the problem. Our models allow us to predict the $\delta$-intervals within which a certain final number of drops are expected. The comparison with experimental data shows a good agreement with the model that explicitly considers the Stokes flow developed in the filaments neck region that lead to breakup points. Also, numerical simulations, that solve the Navier-Stokes equations along with slip boundary condition at the contact lines, are implemented to describe the dynamics of the problem.