Assembly of Gold Nanowires by Sedimentation from Suspension: Experiments and Simulation

Abstract

We investigated the ordering of gold nanowires that settled from aqueous suspension onto a glass substrate due to gravity. The nanowires, ca. 300 nm in cross-sectional diameter and ca. 2, 4, or 7 microns in length, were coated with 2-mercaptoethanesulfonic acid to provide electrostatic repulsion and prevent aggregation. The layer of nanowires in direct contact with the substrate was examined from below using optical microscopy and found to exhibit smectic-like ordering. The extent of smectic ordering depended on nanowire length with the shortest (2 μm) nanowires exhibiting the best ordering. To understand the assembly in this system, we used canonical Monte Carlo simulations to model the two-dimensional ordering of the nanowires on a substrate. We accounted for van der Waals and electrostatic interactions between the nanowires. The simulations reproduced the experimental trends and showed that roughness at the ends of the nanowires, which locally increased electrostatic repulsion, is critical to correctly predicting the experimentally observed smectic ordering.

Engineering of Micro‐ and Nanostructured Surfaces with Anisotropic Geometries and Properties

“…As a result, direction by evaporative or capillary assembly is an especially useful means of ordering particles, by crystallization at the liquid-air interface or by packing at the three-phase contact line. [ 240 ] In one example, CdTe nanotetrapods (100 nm arms) were collected from solution at the three-phase contact line, and positioned within lithographically pre-patterned cavities on a substrate during evaporation of a droplet. [ 241 ] When the cavity width was approximately the width of two arms the tetrapods oriented reliably with two arms facing towards the channel.…”

Asymmetric van der Waals Forces Drive Orientation of Compositionally Anisotropic Nanocylinders within Smectic Arrays: Experiment and Simulation

“…Experimental assemblies typically have sufficient particles to form between two to three monolayers, and hence are not two-dimensional, however we are only able to image the bottom layer. 10 …”

“…41–45 Coatings can be added post-synthesis. 9,10,44–49 These not only allow surface functionalization but also can provide the additional opportunity to etch away some segments leaving behind air- or solvent-filled gaps, with the structure maintained by the coating material. 8,9,45–47,50–52 Hence, the materials properties of the segments along the length of these particles can be varied over a large range.…”

“…10 In that work, we were able to attribute the experimental observation of smectic rows to a balance of vdW and electrostatic interactions using Monte Carlo (MC) simulations in a coarse-grained model of the Au nanowires. 10 …”

Gardens of Eden in systems of bistable nanoscopic wires

“…The magnetostatic interaction between the wires modifies the loops and therefore it is relevant for future ultrahigh density data storage [7,8]. The interaction combined with applied field allows preparation of fluid suspensions where the nanowires form ordered structures [9,10] (see also the option of electrostatic interaction [11]). When solidified to composites [12], the structures offer hysteresis loops with tunable properties.…”