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

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 SiO2 flat surface, and then they are melted by laser irradiation with ∼ 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, δ, between the square sides' lengths and their widths is an essential parameter of the problem. Our models allow us to predict the δ-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. * Electronic address: aggonzal@exa.unicen.edu.ar arXiv:1805.07304v2 [physics.flu-dyn]

Liquid-State Dewetting of Pulsed-Laser-Heated Nanoscale Metal Films and Other Geometries

“…The process is repeated sequentially in the remaining filaments after the breakup of the bulges forming drops until the final pattern of particles is obtained. The estimates based on detailed analysis of this process of the distances between drops and the final number of particles show a remarkable agreement with experiments carried out with Cu rectangular grids (Cuellar et al 2018).…”

“…An alternative approach to directing instability is to consider a fully two-dimensional setup and then, instead of a single filament, focus on a rectangular mesh of filaments. Studies show that besides the drops at the nodes, the number of drops per side of the rectangle can be predicted by considering the process of retraction and breakup of finite filaments (Cuellar et al 2017(Cuellar et al , 2018. The dewetting process along the filament at its ends is like a snowplow that leads to the formation of a bulge at their tips, which is concomitant with a wetting process in the transverse direction of original filament.…”

Signatures of slip in dewetting polymer films

“…1 are not global but local minimizers of scriptE and thereby, also represent viable stationary states. While droplet patterns emerging from the spinodal dewetting feature seemingly random distributions of droplets with details depending on intermolecular interactions (30, 31), droplet distributions in other flow scenarios are reminiscent of the process that leads to their creation (e.g., heterogeneous nucleation, surface instabilities on patterned substrates, droplet production in confined environments, or even dynamically for sliding droplets) (32–38). This raises the natural question: Which mechanism decides what pattern is generated?…”

Formación de estructuras bidimensionales mediante flujos de recubrimiento inestables

“…buena [31].En efecto, para h g = 10 nm, se ha medido un ancho promedio de (78,2 ± 3,6) nm, mientras que el valor calculado es de (80,7 ± 7) nm.…”

“…En el caso del filamento apoyado, el proceso de ruptura implica un movimiento de demojado (o retroceso) de la línea de contacto en la zona del cuello y, a su vez, otro de mojado (o avance) en las zonas laterales a dicho cuello por efecto de conservación de masa. En esta tesis trataremos fenómenos de ruptura de filamentos líquidos con línea de contacto en escalas milimétrica [30] y nanométrica [31]. Estudios experimentales [5,32] y teóricos [22] sugieren que el tipo de patrón de gotas que surge como consecuencia de la ruputura de los filamentos depende fuertemente de las propiedades de mojabilidad entre el líquido y el sustrato.…”