Alyssa J. Pasquale

Genetically engineered plasmonic nanoarrays

In the present Letter, we demonstrate how the design of metallic nanoparticle arrays with large electric field enhancement can be performed using the basic paradigm of engineering, namely the optimization of a well-defined objective function. Such optimization is carried out by coupling a genetic algorithm with the analytical multiparticle Mie theory. General design criteria for best enhancement of electric fields are obtained, unveiling the fundamental interplay between the near-field plasmonic and radiative photonic coupling. Our optimization approach is experimentally validated by surface-enhanced Raman scattering measurements, which demonstrate how genetically optimized arrays, fabricated using electron beam lithography, lead to order of ten improvement of Raman enhancement over nanoparticle dimer antennas, and order of one hundred improvement over optimal nanoparticle gratings. A rigorous design of nanoparticle arrays with optimal field enhancement is essential to the engineering of numerous nanoscale optical devices such as plasmon-enhanced biosensors, photodetectors, light sources and more efficient nonlinear optical elements for on chip integration.

Concentric Necklace Nanolenses for Optical Near-Field Focusing and Enhancement

In this paper, we design and analyze concentric necklace nanolenses (CNNLs) which consist of metal nanoparticle dimers placed in the center of one or more concentric rings of plasmonic necklaces. We use three-dimensional finite-difference time-domain simulations, electron-beam lithography fabrication, dark-field scattering analysis, and surface-enhanced Raman scattering (SERS) measurements to investigate the far-field scattering and near-field light localization properties of CNNLs. Using these methods, we show that CNNLs display far-field scattering properties that arise from coupling between the dimer and surrounding necklace(s), leading to two pronounced peaks in single-necklace CNNLs and three pronounced peaks in double-necklace CNNLs. In our near-field analysis, we find that the number of particles in the surrounding necklace is an important degree of freedom in the optimization of near-field intensity within the dimer hot-spot region. By using CNNLs where the necklace diameters have a diameter equal to an integer multiple of the resonance wavelength of the isolated dimer times a constant scaling factor, the intensity of near-fields can be optimized for all geometries over a broad-band wavelength range. Using optimized geometries, we perform SERS experiments on CNNLs coated with a pMA monolayer and demonstrate 7× Raman enhancement in the single-necklace CNNL and 18× enhancement in the double-necklace CNNL over the reference dimer antenna geometry, with an average Raman enhancement value of approximately 7 × 10(5).

Plasmon-enhanced isotropic structural coloration of metal films with homogenized Pinwheel nanoparticle arrays

We design and demonstrate angle-insensitive structural color by engineering plasmonenhanced light scattering from homogenized Pinwheel arrays of Au nanoparticles on Au substrate for plasmonic applications, like displays, security tagging and solar cells.

Engineering photonic-plasmonic aperiodic surfaces for optical biosensing

The ability to reproducibly and accurately control light matter interaction on the nanoscale is at the core of the field of optical biosensing enabled by the engineering of nanophotonic and nanoplasmonic structures. Efficient schemes for electromagnetic field localization and enhancement over precisely defined sub-wavelength spatial regions is essential to truly benefit from these emerging technologies. In particular, the engineering of deterministic media without translational invariance offers an almost unexplored potential for the manipulation of optical states with vastly tunable transport and localization properties over broadband frequency spectra. In this paper, we discuss deterministic aperiodic plasmonic and photonic nanostructures for optical biosensing applications based on fingerprinting Surface Enhanced Raman Scattering (SERS) in metal nanoparticle arrays and engineered light scattering from nanostructured dielectric surfaces with low refractive index (quartz).