Drew DeJarnette

Spectral patterns underlying polarization-enhanced diffractive interference are distinguishable by complex trigonometry

Superpositioned modes from scatterers in periodic arrays that prescribe spectral interference patterns are distinguishable using an analytic description. Interference arising from irradiation of ordered lattices with polarizable components yields far-field spectral patterns in which extraordinary features appear at resonant frequencies associated with lattice geometry. Organization of nanostructures utilizing these features has been limited by complexity of electrodynamic descriptions for coupling between these plasmon resonance energies and diffracted spectral modes. The trigonometric description shows how changing lattice constant and incident wavelength to adjust coupling between phase-dependent constructive interference and isometric values of plasmonic gold nanostructure polarizability results in extraordinary spectral features.

Far-field Fano resonance in nanoring lattices modeled from extracted, point dipole polarizability

Coupling and extinction of light among particles representable as point dipoles can be characterized using the coupled dipole approximation (CDA). The analytic form for dipole polarizability of spheroidal particles supports rapid electrodynamic analysis of nanoparticle lattices using CDA. However, computational expense increases for complex shapes with non-analytical polarizabilities which require discrete dipole (DDA) or higher order approximations. This work shows fast CDA analysis of assembled nanorings is possible using a single dipole nanoring polarizability extrapolated from a DDA calculation by summing contributions from individual polarizable volume elements. Plasmon resonance wavelengths of nanorings obtained using extracted polarizabilities blueshift as wall dimensions-to-inner radius aspect ratio increases, consistent with published theory and experiment. Calculated far-field Fano resonance energy maximum and minimum wavelengths were within 1% of full volume element results. Considering polarizability allows a more complete physical picture of predicting plasmon resonance location than metal dielectric alone. This method reduces time required for calculation of diffractive coupling more than 40 000-fold in ordered nanoring systems for 400–1400 nm incident wavelengths. Extension of this technique beyond nanorings is possible for more complex shapes that exhibit dipolar or quadrupole radiation patterns.

Selective spectral filtration with nanoparticles for concentrating solar collectors

Abstract. A spectral fluid filter for potential use in hybrid photovoltaic/thermal concentrating solar collectors has been developed, targeting maximum absorption above and transmission below a desired wavelength. In this application, the temperature-dependent bandgap of the potential solar cell is used in the optimization of the filter. Dispersing a mix of colloidal nanoparticles in a heat transfer fluid is shown to absorb 86% of sub-bandgap insolation while absorbing only 18% above bandgap insolation. Transmission above bandgap light would be directly absorbed into the photovoltaic (PV) cell while absorbed photons transfer energy directly into the heat transfer fluid ultimately reducing the number of heat transfer steps. Placement of a filter in front of the PV cell is shown to decrease losses by converting an additional 2% of the total solar energy into thermal energy since it allows recollection of light reflected off the receiver.

Plasmonic nanoparticle based spectral fluid filters for concentrating PV/T collectors

We propose a design for a concentrating PV/T collector utilizing plasmonic nanoparticles directly suspended in the working fluid to spectrally filter the incoming solar flux. This liquid filter serves two purposes: the direct capture of thermal energy as well as filtering off of key portions of the spectrum before transmission to the PV cell. Our device builds upon the current Cogenra T14 system with a two-pass architecture: the first pass on the back side of the PV cell pre-heating the fluid from any thermalization losses, and the second pass in front of the PV cell to achieve the spectral filtering. Here we present details on the selection of plasmonic nanoparticles for a given cell bandgap as well as the impact to the overall system pumping power and cost.

A Parametric Investigation of a Concentrating Photovoltaic/Thermal System With Spectral Filtering Utilizing a Two-Dimensional Heat Transfer Model

A 2D heat transfer model of a hybrid photovoltaic/thermal (PV/T) system has been created. This paper investigates the impact of ideal filters to best accommodate for a nonuniform PV temperature along the length of the receiver. The proposed configuration consists of a GaAs cell laminated to an aluminum extrusion. The working fluid, a transparent high-temperature heat transfer fluid with suspended nanoparticles, flows through the hollow extrusion where it cools the PV cell before it is redirected in front of the cell acting as an optical filter. The model accounts for PV cell efficiency, temperature, and bandgap dependence, the details often neglected in prior works.

Filtering light with nanoparticles: a review of optically selective particles and applications

The ability to selectively and controllably interact with light is useful to a wide range of devices. With the advent of nanotechnology, we now have the ability to create optical materials, which are designed from the bottom up, with dimensions of the order of the wavelength of light. While it has been known for some time that nanoparticles exhibit such exciting properties, recent (widespread) research in nanoparticles has significantly increased our understanding of how to fabricate and use nanoparticles for a myriad of enduring and emerging optical applications. Drastic modifications to the “bulk” optical properties of standard materials in these applications are possible, enabling “nano-engineered” optical properties with several degrees of design freedom, including material, size, morphology, surrounding media, and nearby structures. Understanding these sensitivities has led to optical control from the ultraviolet through the infrared spectrum. To highlight this, the following review provides a comprehensive snapshot of how these effects have been captured in models and experimentally demonstrated in terms of spectral selectivity in absorption, scattering, and emission. In addition, we discuss recent progress toward using nanoparticles in real applications, most commonly in fluid suspensions or solid thin films as a means to create the next generation of highly scalable and (potentially) low-cost spectrally selective optical materials.

Design and feasibility of high temperature nanoparticle fluid filter in hybrid thermal/photovoltaic concentrating solar power

A nanoparticle fluid filter used with concentrating hybrid solar/thermal collector design is presented. Nanoparticle fluid filters could be situated on any given concentrating system with appropriate customized engineering. This work shows the design in the context of a trough concentration system. Geometric design and physical placement in the optical path was modeled using SolTrace. It was found that a design can be made that blocks 0% of the traced rays. The nanoparticle fluid filter is tunable for different concentrating systems using various PV cells or operating at varying temperatures.

Compact simulation guides subnanometer, femtosecond measures of energy transfer between quasiparticles and hot carriers at interfaces between metals and two-dimensional materials

Compact computational structure-function relations are needed to examine energy transfer between confined fields and carrier dynamics at heterostructure interfaces. This work used discrete dipole approximations to analyze quasiparticle excitation and dephasing at interfaces between metals and van der Waals materials. Simulations were compared with scanning transmission electron microscopy (STEM) for energy electron loss spectroscopy (EELS) at sub-nanometer resolution and femtosecond timescale. Artifacts like direct electron-hole pair generation were avoided. Comparing simulation with experiment distinguished quasiparticle energy transfer to hot carriers at the interface, and supported development of structure-function relations between interface morphology and emergent discrete and hybrid modes.

Fabrication and comparison of selective, transparent optics for concentrating solar systems

Concentrating optics enable solar thermal energy to be harvested at high temperature (<100oC). As the temperature of the receiver increases, radiative losses can become dominant. In many concentrating systems, the receiver is coated with a selectively absorbing surface (TiNOx, Black Chrome, etc.) to obtain higher efficiency. Commercial absorber coatings are well-developed to be highly absorbing for short (solar) wavelengths, but highly reflective at long (thermal emission) wavelengths. If a solar system requires an analogous transparent, non-absorbing optic – i.e. a cover material which is highly transparent at short wavelengths, but highly reflective at long wavelengths – the technology is simply not available. Low-e glass technology represents a commercially viable option for this sector, but it has only been optimized for visible light transmission. Optically thin metal hole-arrays are another feasible solution, but are often difficult to fabricate. This study investigates combinations of thin film coatings of transparent conductive oxides and nanoparticles as a potential low cost solution for selective solar covers. This paper experimentally compares readily available materials deposited on various substrates and ranks them via an ‘efficiency factor for selectivity’, which represents the efficiency of radiative exchange in a solar collector. Out of the materials studied, indium tin oxide and thin films of ZnS-Ag-ZnS represent the most feasible solutions for concentrated solar systems. Overall, this study provides an engineering design approach and guide for creating scalable, selective, transparent optics which could potentially be imbedded within conventional low-e glass production techniques.

Polarizability extraction for rapid computation of Fano resonance in nanoring lattices

Rapid modeling of far-field Fano resonance supported by lattices of complex nanostructures is possible with the coupled dipole approximation (CDA) using point, dipole polarizability extrapolated from a higher order discrete dipole approximation (DDA). Fano resonance in nanostructured metamaterials has been evaluated with CDA for spheroids, for which an analytical form of particle polarizability exists. For complex structures with non-analytic polarizability, such as rings, higher order electrodynamic solutions must be employed at the cost of computation time. Point polarizability is determined from the DDA by summing individual polarizable volume elements from the modeled structure. Extraction of single nanoring polarizability from DDA permitted CDA analysis of nanoring lattices with a 40,000-fold reduction in computational time over 1000 wavelengths. Maxima and minima of predicted Fano resonance energies were within 1% of full volume elements using the DDA. This modeling technique is amenable to other complex nanostructures which exhibit primarily dipolar and/or quadrupolar resonance behavior. Rapid analysis of coupling between plasmons and photon diffraction modes in lattices of nanostructures supports design of plasmonic enhancements in sustainable energy and biomedical devices.