Self-Assembly of Spheres on a Cone Surface

Self-assembly in confined space can lead to formation of unique 3-D structures. We study self-assembly of submicron-sized colloidal spheres on the surface of a micron-sized cone. Fabrication of micron-sized cones is challenging using conventional photolithography. We explored alternative techniques for fabrication of cones. By using a 3-D laser lithography tool called Nanoscribe, we successfully manufactured cones of various cone angles and diameters. By using a micropipette puller, we pulled glass capillary tubes into cones with very smooth surfaces. We performed experiments to self-assemble colloidal spheres on both types of conical surfaces. To assemble spheres, we use depletion interaction. It results in a short-ranged attraction between the spheres, and between the spheres and the conical surface. We observed crystal growth on the cones that were fabricated from glass capillary tubes. This result suggests that a smoother cone surface is preferred to study self-assembly on a cone using depletion interaction.