Self-organizing Dimer Formation of Silver Nanocubes through Face Selective Functionalization and Surface Plasmon Coupling at Its Fractal Junction

Abstract

We have demonstrated the dimerization of single-crystalline Ag nanocubes with reasonably high yields through stepwise integration by following three steps: the preparation of a single layer of densely packed Ag nanocubes on a substrate by modified convective assembly, the selective functionalization of the upper face of the Ag nanocubes with a hydrophobic DT-SAM using the μCP approach, and the spontaneous dimerization in a mixture of ethanol and water driven by enhanced anisotropic hydrophobic interparticle interactions. Face-selective functionalization using hydrophobic DT-SAM gave the nanocubes directionality with respect to their anisotropic interparticle interactions under an external hydrophilic environment. We conclude that the driving force that reduced the surface area of the hydrophobic faces is sufficient large to form an ordered assembly of nanosized building blocks in an aqueous solution. Both experimental and theoretical studies revealed that the 50-nm-diameter Ag nanocubes dimers with a ca. 3.3 nm gap at their junction exhibited two plasmon peaks centered at 446 nm and 600 nm, which contributed to transverse and longitudinal plasmon resonances, respectively. Elctromagnetic calculations based on the FDTD method clearly showed that a greater enhancement of the local field occurred, with an average amplitude of the electric field of 1.0×1015, at the fractal space between the aggregated Ag nanocubes when the dimer was illuminated under longitudinally polarized light.