In a collaboration with Chad Mirkin, we are studying 3D superlattices of gold or silver nanoparticles fabricated with DNA linkers, which provide many opportunities for making materials with unusual including switchable optical properties.  The simplest structure consists of bcc superlattices of gold or silver nanoparticles, whose optical properties are well described with effective medium theory.  Well defined crystal habits of these superlattices lead to rhombic dodecahedral micron size crystals, which show Fabry-Perot resonances that couple to the gold plasmon excitation to produce a band-gap.  If ethanol is added to the DNA-superlattices, the lattices shrink dramatically but reversibly, even undergoing counterion condensation, with significant red-shifts in the plasmon.  If dye molecules are added selectively to the DNA, one can create luminescent superlattices with properties that are sensitive to the distance between the gold particles and dye molecules (showing both quenching, extinction and enhancement effects) and the resulting angular dependence of the emission is especially sensitive to the wavelength dependence of extinction and enhancement.  Superlattices with octahedral particles show structural properties that are similar to those with spherical particles, but their extinction shows significant polarization anisotropy. <br/>In a collaboration with Teri Odom, we have studied 2D lattices that show hybrid modes involving photonic modes of the lattice, and plasmons associated with silver, gold or aluminum particles. In recent work, it has been demonstrated that the aluminum lattices can exhibit quadrupole lattice plasmons in addition to the normal dipole mode lattice plasmons. Using classical electrodynamics we are able to describe the many unusual properties of these quadrupole lattice plasmons.<br/>

Nanoparticle superlattices in 2D and 3D

254th National Meeting (2017)

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