Large-scale self-assembly of dispersed nanodiamonds

Well-aligned rectangular-shaped nanodiamond fibers (NDFs) with a length-to-width ratio of over 1000 were formed on a large-scale via a self-assembly process by drying acid-treated nanodiamonds of a uniform size ( 4 nm) from an aqueous solution. Nanodiamond thin films (NDTFs), instead of NDFs, have also been prepared by drying the aqueous ND dispersion at a sufficiently low temperature (< 70 C)) and/or a sufficiently low pH (< 4). Detailed conditions, including pH and temperature, for the formation of NDFs and NDTFs via the drying process, together with the structure and property of the resultant nanodiamond assemblies were investigated. The formation of NDFs and NDTFs was found to result from the delicate interplay between the ND–ND, ND–H2O, and ND–substrate interactions under the water-evaporation-induced directional convection flow. The resultant NDFs were demonstrated to show a bandgap of 4.5 eV.