Interfacial-tension-directed self-assembly of nanowires on superhydrophobic surfaces

This paper describes a novel method of nanowire assembly using a superhydrophobic surface as a template. Well-defined superhydrophobic structures on a template surface direct the site-specific self-assembly of nanowires due to interfacial tension in evaporation, enabling simple but highly-efficient and ordered assembly of nanowires. High-aspect-ratio (HAR) microstructures with tapered tips are fabricated by deep reactive ion etch (DRIE) and are coated with a self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) for hydrophobicity. Nickel nanowires are fabricated in a porous alumina membrane by electrodeposition. A uniformly-dispersed nanowire suspension is dispensed and evaporated on the superhydrophobic template surface. Due to surface superhydrophobicity, a three-phase (i.e., liquid-solid-gas) interface is created on the surface structures, enabling the nanowires to reside only over the interface. After complete evaporation, the nanowires are mostly left on the structural tips, driven by the interfacial forces constituted at the three-phase boundary. Although the alignment yield rate of the nanowires to the surface pattern has not reached 100%, current experimental results demonstrate that the idea of using interfacial tension on superhydrophobic surfaces can serve as a novel nano-assembly technique with high throughput and high rate. The key parameters affecting the yield of self-assembly and alignment will continue to be studied for further improvement.