Fabrication and wetting properties of metallic half-shells with submicron diameters

The deposition of a thin, metal film onto an array of spherical silica colloids, followed by dissolution of the colloidal template, produces metallic half-shells with nanometer-scale dimensions. Half-shells of gold, platinum, and palladium were fabricated with diameters of the particles ranging from 100 to 500 nm, and shell thicknesses of 8-15 nm. The half-shells have three useful properties because of their geometries: (i) a high ratio of surface area to volume, (ii) a large length of edge relative to size, and (iii) an entropic resistance to assembling into close-packed structures. The surface properties of these half-shells can be modified with self-assembled monolayers (SAMs), formed by adsorption of alkanethiols. The surfaces composed of aggregated gold half-shells are superhydrophobic; the measured contact angle of water on a surface of unmodified gold half-shells was similar to151degrees and on a surface of gold half-shells functionalized with a hexadecanethiolate SAM was similar to163degrees. Aggregates of half-shells were patterned using template-assisted self-assembly.