Microwell‐Directed Self‐Assembly of Vertical Nanowire Arrays

Vertical arrays of anisotropic particles are desired for many applications including solar cells, battery electrodes, and lasers. Partially etched nano­wires (PENs) are hybrid silica nanotube/nanowires with partial metallic cores. These particles spontaneously form vertical arrays in which on average 70% of the particles are oriented perpendicular to the underlying substrate. Here, we perform PEN self‐assembly on lithographically prepared substrates patterned with square microwells having dimensions comparable to the length of the particles. Particle self‐assembly is observed both in the microwells and on the intervening surfaces. PENs both directly deposit into a well and diffuse across the surface between microwells until falling into a well. Assembly occurs as the local concentration of PENs in a well increases by these two mechanisms. Microwells provide a way to control array location on a surface and improve standing percentages up to 100% when the edge dimensions are decreased to a size approximately equal to the nanowire length. Micro­wells also protect against array disruption during sample drying.