Monodisperse Copper Nanocubes: Synthesis, Self-Assembly, and Large-Area Dense-Packed Films

In comparison to the well-characterized bottom-up synthesis of Au and Ag nanomaterials, the synthesis of Cu nanocrystals with well-defined and controllable shapes is still in need of improvement. Among the many shapes, a cube covered by six {100} facets can be regarded as a standard model to study the surface properties of {100} facets. Herein, we have prepared monodisperse Cu nanoparticles having a slightly truncated cubic shape with an average edge length of 75.7 nm and a standard deviation of 3.87% by using CuCl as the precursor, oleylamine as the reaction solvent, and trioctylphosphine and octadecylamine as shape control agents. The as-prepared Cu nanocubes tend to self-assemble on transmission electron microscopy grids or silicon substrates. Electron microscopy and small-angle X-ray scattering reveal that the Cu nanocubes prefer to self-assemble into 2D or 3D rhombohedral structures (RS). Large-area dense-packed films (1.5 cm X 2.5 cm) composed of monodisperse Cu nanocubes were fabricated by immersing a Si substrate in a dispersion of dodecanethiol-capped Cu nanocubes in toluene and evaporating the toluene at a controlled rate while holding the substrate at an angle. The electrical properties of the Cu films with various thickness and annealing temperatures were studied.