Nanorod self-assembly for tuning optical absorption

摘要

Metallic nanoparticles that absorb and concentrate light are leading to greater efficiencies in nanophotonic devices. By confining gold nanorods (Au NRs) in a polymer film, we can control their spacing and orientation and, in turn, the absorption and polarization characteristics of the nanocomposite. In this study, we systematically increase the volume fraction of Au NRs (φ_(rod)) (aspect ratio ν = 3.3) while maintaining a uniform dispersion. As φ_(rod) increases from 1 to 16 vol %, the spacing between rods decreases from 120 to 20 nm and scales as φrod~(-0.4). Simultaneously, the local 2D orientational order parameter increases linearly with φ_(rod), although the rods are globally isotropic. The Au NR dispersion is found to depend on the enthalpic interactions between poly(ethylene glycol) brush grafted to the Au NRs and the poly(methyl methacrylate) matrix chains. Furthermore, the plasmon resonance exhibits a red shift with increasing φ_(rod), and coupling is observed for separations up to 70 nm. Because NR spacing and orientation can be finely controlled using polymer matrix, these films are ideally suited for understanding fundamental behavior (e.g., plasmon coupling) as well as practical devices (e.g., solar cells).