Defect tolerance and the effect of structural inhomogeneity in plasmonic DNA-nanoparticle superlattices

Abstract

Bottom-up assemblies of plasmonic nanoparticles exhibit unique optical effects such as tunable reflection, optical cavity modes, and tunable photonic resonances. Here, we compare detailed simulations with experiment to explore the effect of structural inhomogeneity on the optical response in DNA-gold nanoparticle superlattices. In particular, we explore the effect of background environment, nanoparticle polydispersity (>10%), and variation in nanoparticle placement (∼5%). At volume fractions less than 20% Au, the optical response is insensitive to particle size, defects, and inhomogeneity in the superlattice. At elevated volume fractions (20% and 25%), structures incorporating different sized nanoparticles (10-, 20-, and 40-nm diameter) each exhibit distinct far-field extinction and near-field properties. These optical properties are most pronounced in lattices with larger particles, which at fixed volume fraction have greater plasmonic coupling than those with smaller particles. Moreover, the incorporation of experimentally informed inhomogeneity leads to variation in far-field extinction and inconsistent electric-field intensities throughout the lattice, demonstrating that volume fraction is not sufficient to describe the optical properties of such structures. These data have important implications for understanding the role of particle and lattice inhomogeneity in determining the properties of plasmonic nanoparticle lattices with deliberately designed optical properties.T he rational arrangement of nanoparticles in multiple dimensions is a promising means for creating materials with novel properties not found in nature. Noble metal nanoparticles are interesting material building blocks due to their ability to amplify local fields by orders of magnitude and scatter light well below the diffraction limit. These efficient interactions with visible light are due to localized surface plasmon resonances (LSPRs), the collective oscillation of conduction electrons (1). Hierarchical arrangements of plasmonic nanoparticles have become the basis for colorimetric sensors (2, 3), subdiffraction limited waveguides (4), visible light metamaterials (5), and nanoscale lasing devices (6, 7), and the ability to adjust architecture in such materials has led to a wide variety of structures with tunable and unusual optical properties (8-12). Many of these technologies leverage the scalability and modularity of bottom-up assembly techniques, which use chemically synthesized colloidal nanoparticles as building blocks (13,14). Unfortunately, all nanoparticle assembly techniques result in materials with structural defects across multiple length scales, including imprecise particle placement, grain boundaries, and variation in crystallite size. In addition, the nanoparticles used in these systems are inherently inhomogeneous: varying in size, shape, and radius of curvature. Although the effects of inhomogeneity have been investigated at the individual nanoparticle level (15, 16), the effects of inhomogeneity on plasmonic assemblies are...

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