Self-Aligned Anisotropic Plasmonic Nanostructures.

Great opportunities emerge not only in the generation of anisotropic plasmonic nanostructures but also in controlling their orientation relative to incident light. Herein, a stepwise seeded growth method is reported for the synthesis of rod-shaped plasmon nanostructures which are vertically self-aligned with respect to the surface of colloidal substrates. Anisotropic growth of metal nanostructure is achieved by depositing metal seeds onto the surface of colloidal substrates and then selectively passivating the seed surface to induce symmetry breaking in the subsequent seed-mediated growth process. The versatility of this method is demonstrated by producing nanoparticle dimers and linear trimers of Au, Au-Ag, Au-Pd, and Au-Cu O. Further, this unique method enables the automatic vertical alignment of the resulting plasmonic nanostructures to the surface of the colloidal substrate, thereby making it possible to design magnetic/plasmonic nanocomposites that allow the dynamic tuning of the plasmon excitation by controlling their orientation using an external magnetic field. The controlled anisotropic growth of colloidal plasmonic nanostructures and their dynamic modulation of plasmon excitation further allow them to be conveniently fixed in a thin polymer film with a well-controlled orientation to display polarization-dependent patterns that may find important applications in information encryption.