Oriented Assembly of Gold Nanorods on the Single-Particle Level

Non-spherical colloidal nanoparticles have great potential for applications owing to their enhanced directional properties. However, the lack of methods to precisely assemble them on surfaces has hindered exploitation of their properties for planar devices. Here, the oriented assembly of short gold nanorods with lengths below 100 nm from colloidal suspensions is demonstrated. A locally induced phase transition confines the colloidal nanorods at a receding three-phase contact line that is controllably moved over a nanostructured surface in a capillary assembly process. Dedicated topographical trapping sites allow for aligned assembly of the nanorods on the single-particle level. The feasibility of this method is demonstrated by assembling nanorods into long-range-ordered, non-close packed arrays that could serve as anti-counterfeit labels by virtue of their distinct optical appearance in the far-field. Furthermore, oriented nanorod dimers that are deterministically assembled have the potential to function as nano-plasmonic antenna devices.