Assembly of Gold Nanoparticles into Microwire Networks Induced by Drying Liquid Bridges

Large interconnected gold wire structures ($\sim {\mathrm{cm}}^2$) of different topologies have been made by the drying of a gold nanoparticle suspension that has formed a connected network of liquid bridges in the interstices between a 2D crystalline layer of latex particles and a substrate. Slow evaporation of the suspending medium assembles the nanoparticles into a periodic or disordered conducting network of micrometer thick gold wires on the substrate. The presence of surfactants in the suspension is critical to maintaining the stability of the liquid bridge network during the evaporation process.

Figure 1

Microscopic images of disordered and ordered microwire patterns formed on substrates by evaporative assembly of a gold nanoparticle suspension using (a) $100\mu \mathrm{m}$, (b) and (c) $50\mu \mathrm{m}$ latex particles template on planar glass surfaces, and (d) microwire patterns on a monolayer of $100\mu \mathrm{m}$ latex particles. Images (a), (b) were taken from the bottom of the substrate and (c), (d) were top observations.

Figure 2

Schematic of the lithography procedure: (a) 2D latex particle crystal template on a glass slide, (b) doping with gold nanoparticle suspension, (c) drying, and (d) latex particles removal.

Figure 3

(a),(b),(c) Consecutive microscopy snapshots viewed from the bottom of the substrate on a $400\times 650\mu \mathrm{m}$ area of the latex particle crystal that tracks the formation of the liquid bridge network on the substrate. The light dots mark the latex particle-glass contacts and the bright opening the progression of the air-substrate area. (d),(e),(f) $100\times 200\mu \mathrm{m}$ images of the evaporative thinning stages of a single liquid bridge on the substrate that joins two pendular rings of liquid at the base of two neighboring latex particles and the final assembly of Au NP into a microwire joining the “nodes” around the base of the latex particles. (g) Top view microscopy image of a microwire node that resembles a solder spot after removal of the template latex particles. The microwires are all connected at the base of the node on the substrate as seen in (d)–(f). (See supplementary material for a video of the entire process [18].)

Figure 4

Microscopy images from the bottom of the substrate of stable and unstable liquid bridges formed on the substrate (coincident with the focal plane) joining the pendular rings at the base of two contacting latex particles. Liquid bridges formed from (a), (b) pure water (surface tension $72\mathrm{mN}/\mathrm{m}$) and (d), (e) pure 2-propanol (surface tension $21\mathrm{mN}/\mathrm{m}$) break up during drying but remain stable when 0.1 mM of SDS was first added to the (c) water and (f) 2-propanol.

Figure 5

Schematic diagram of (a) fast drying with meniscus pinning by nanoparticle agglomeration at the three-phase contact line and (c) slow drying that leads to solute nanoparticle consolidation. Examples for drying pattern around a $100\mu \mathrm{m}$ latex particle at (b) $90°\mathrm{C}$ and (d) $4°\mathrm{C}$ that illustrates the corresponding cases.