Plasmonic nanoparticles can be used to engineer radiation decay of a dipole in close proximity to the surface of the particle. In this talk I will review our recent theoretical and experimental results on the enhancement and quenching of radiation from a dipole in close proximity to a silver or gold nanoparticle of a few different sizes. We apply the theory of radiation decay engineering to explain our recent experimental results of enhancement of exciton emission in a composite semiconductor thin film decorated with gold nanoparticles.
Plasmonic nanoparticles can be used to engineer radiation decay of a dipole in close proximity to the surface of the particle. We present a theoretical analysis of the quantum yield of an electric dipole near a silver or gold nanoparticle of several different sizes. Specifically, we detail the calculation and simulation of the normalized quantum yield of an electric dipole coupled with a plasmonic nanoparticle. We find that the local electric field near the electric dipole is enhanced and has its characteristics altered.
Optical properties of a plasmonic metasurface made of a monolayer of gold nanoparticles in close proximity to an aluminum thin film were studied numerically and experimentally. Extinction spectra of the plasmonic metasurface were studied as functions of the thickness of a dielectric spacer between the monolayer of gold nanoparticles and the aluminum film in the visible wavelength range. The goal was to study the excitation of a collective surface plasmon resonance (SPR) mode and a gap plasmon mode as well as their dependence on the spacer thickness, nanoparticles spacing and their size. By using finite-difference-time-domain (FDTD) calculations we find that the SPR extinction peak first red-shifts and then splits into two peaks. The first extinction peak is associated with the collective SPR mode of the monolayer and it shifts to shorter wavelengths as the spacer layer decreases. As the spacer layer decreases from 35 nm to 7.5 nm, the second peak gradually appears in the extinction spectra of the metasurface. We assign the second peak to the gap mode. The gap mode first appears at around 620 nm or greater and it shifts to larger wavelength for larger nanoparticle spacing and size. The FDTD simulations are confirmed by an examination of the dispersion curves of a similar multilayer system. The computational results match the experimental results and confirm the excitation of the two modes.
Hyperbolic metamaterials can propagate electromagnetic modes with unusually large wave numbers (extraordinary high-momentum modes). The extraordinary high-momentum modes are non-propagating or evanescent modes in common optical media. On the other hand, hyperbolic metamaterials can sustain propagating electromagnetic waves with unusually low wave numbers (extraordinary low-momentum modes). Both extraordinary high- and low-momentum modes are of special interest for a number of applications. For example, the development of these exotic modes, which are fundamental to the operation of hyperlenses, might lead to unprecedented sub-diffraction optical imaging systems. Hyperbolic metamaterials are also of special interest for radiative decay engineering.
The inevitable trade-off between optical mode confinement and the optical losses inherent to the metal component is a fundamental challenge for plasmonics and metamaterials. We have carried out numerical analysis of Rytov’s dispersion equations to model loss-compensation in metal-semiconductor hyperbolic metamaterials with extraordinary high- and extraordinary low-momentum modes. Numerical results provide a framework for the design of loss compensation schemes in hyperbolic metamaterials with extraordinary high- and extraordinary low-momentum modes.
Epsilon Near Zero (ENZ) metamaterials are interest for a broad range of applications in optoelectronics, communication and photovoltaic. Composite metal-dielectric metamaterials can be designed to exhibit ENZ in a specific frequency range. However, the frequency range if the ENZ is oftentimes limited. Recently, we developed a few different routs to designs metal-dielectric metamaterials with a broadband ENZ in the visible and infrared frequency domain. In this talk, I will present a homogenization theory for 1D and 2D metamaterials based on a few different geometries of metal-dielectric composites. Our approach is conceptually simple, elegant, and technically feasible, while its underlying physics is clear. We use a homogenization technique to estimate the real part of the effective permittivity nulling for a few different geometries of metal-dielectric composites. The design of broadband epsilon-near-zero metamaterials have been demonstrated through the solution of an inverse problem. Furthermore, we consider a few different geometries for realization of a broadband ENZ, such as core-shell spherical nanoparticle and nano-cylinders.
Hamaker-Lifshitz constants are used to calculate van der Waals interaction forces between small particles in solution. Typically, these constants are size-independent and material specific. According to the Lifshitz theory, the Hamaker-Lifshitz constants can be calculated by taking integrals that include the dielectric permittivity, as a function of frequency, of the interacting particles and the medium around particles. The dielectric permittivity of interacting metal nanoparticles can be calculated using the free-electron Drude model for metals. For bulk metals, the Drude model does is size independent. However, the conducting electrons in small metal nanoparticles exhibit surface scattering, which changes the complex dielectric permittivity function. Additionally, the Drude model can be modified to include temperature dependence. That is, an increase in temperature leads to thermal volume expansion and increased phonon population, which affect the scattering rate of the electrons and the plasma frequency. Both of these terms contribute significantly to the Drude model for the dielectric permittivity of the particles. In this work, we show theoretically that scattering of the free conducting electrons inside noble metal nanoparticles with the size of 1 – 50 nm leads to size-dependent dielectric permittivity and Hamaker-Lifshitz constants. In addition, we calculate numerically the Hamaker-Lifshitz constants for a variety of temperatures. The results of the study might be of interest for understanding colloidal stability of metal nanoparticles.
The resonance wavelength of collective surface plasmon polariton in a chain of 50 nm gold nanoparticles has been calculated and compared to experimental data. The distance between the nanoparticles in a chain was varied from 100 nm to 1000 nm, and the polarization of the incident light was gradually changed from parallel to perpendicular relative to the axis connecting the nanoparticles in the chain. The calculations explicitly included the near-, middle-, and far-field dipole coupling between the nanoparticles. The numerical results matched the experimental data with less than 2% error. Arrays of noble metal nanoparticles are of interest for plasmonics, nanooptics, photovoltaics, and biochemical applications. They are widely used as biosensors and molecular rulers. Over the last decade, interest has turned towards the localized surface plasmon resonance (LSPR) in single-nanoparticle sensors. Benefits of such an approach include simplicity (it does not require momentum-matching geometry), versatility on the nanoscale level, and the possibility of single-molecule detection. While single-nanoparticle sensors offer a better sensitivity down to a single protein-receptor binding, a high degree of sensor miniaturization tends to result in a worse detection limit because of limited surface coverage. A solution to this problem might be the use arrays of nanoplasmonic sensors, each of which is capable of resolving single protein binding events. Present study provides a background for bio-sensing, waveguiding, and molecular ruler applications.
We present experimental and theoretical study of the transmission of linearly polarized microwaves through a slab of negative index of refraction metamaterials. A metamaterial slab was designed with an extended S-Shaped Split Ring Resonator (ES-SRR) to exhibit a negative index of refraction around 13.25 +/- 0.75 GHz which is a commercially leased microwave band for satellite communications. The metamaterial slab exhibits a pass-band filter transmission behavior around 12.5 GHz to 14 GHz, encompassing the Ku-band.
A deposition technique has been developed to create thin metal surfaces composed of functionalized fluorescent silver nanoparticles on top of glass or plastic substrates. Deposition is controlled through excitation of nanoparticles via a confocal microscope, allowing for rapid surface formation, high resolution patterning and convenient imaging. The functionalization of these nanoparticles can be tailored to a desired application. Initial investigations have demonstrated that surfaces can be designed to mimic the glucan and mannan layers of a fungal cell wall, which in turn can be used to stimulate and study responses from human immune cells.
We present experimental results on angle-dependent microwave response of the double negative microwave metamaterials. Polarization and angle-dependent transmission spectra of two microwave negative index metamaterials were measured. Two sets of S-shape single unit cells were designed for the 12.5 GHz and 20 GHz frequency ranges. Transmission spectra were measured as a function of polarization and incidence angles of the incoming electromagnetic waves.
Microwave negative index metamaterials have been recently characterized by using primarily far-field transmission of flat slabs and wedges to determine transmission losses and index of refraction, respectively. Although these methods are adequate for most purposes, a more complete characterization of spatial transmission is useful to analyze metamaterials in 3-D, for examples, to characterize irregular forms of metamaterials, such as gradients, prisms, and conformal surfaces. We report here the infrared imaging of the transmitted intensity of microwave electromagnetic waves through a prism of the negative index metamaterials.
Controlled deposition of metal nanostructures on various substrates is highly desirable for electronics, photonics, sensing and catalysis. A laser focused beam has been used to deposit metal nanoparticles and nanostructures based on optical forces with diffraction-limited spatial resolution. We demonstrate fabrication of nanostructured silver wires, spots and wire arrays by using a confocal microscope setup, offering highly reproducible nanostructured silver growth and pattern writing. Particularly, laser-deposited silver micro-wires show adjustable electronic conductivities. Taking into accounts the superior spatial resolution and versatile pattern design, this technique is promising for a variety of applications such as microelectronics and bio-chips.
We report far-field optical extinction spectra of linear chains of gold and silver nanocylinders with interparticle
separations close to the particles' surface plasmon resonance (SPR) wavelength. The spectra reveal a typical pattern of
dipole-like and quadrupole SPR peaks and additional non-SPR peaks. We rationalize the extra peaks by constructive
interference of the scattered and incident electromagnetic fields.
We present experimental results on the multicolor (blue and green) photoluminescence from glycine-coated silver
nanoclusters and small nanoparticles which can be used as novel probes for bio-imaging. Glycine-coated silver
nanoclusters and nanoparticles were synthesized using thermal reduction of silver nitrate in a glycine matrix,
according to a modified procedure described in literature. The size characterization with mass spectrometry,
scanning electron microscopy and dynamic light scattering showed that the diameters of luminescent silver
nanoclusters and small nanoparticles vary from 0.5 nm to 17 nm. Extinction spectroscopy revealed that the
absorption band of the luminescent nanoclusters and nanoparticles was blue-shifted as compared to the nonluminescent
larger silver nanoparticles. This effect indicated the well-known size dependence of the surface
plasmon resonance in silver. The most pronounced photoluminescence peak was observed around 410 nm
(characteristic SPR wavelength for silver) which strongly suggests the enhancement of the photoluminescence from
silver nanoparticles by the SPR. The relative quantum yield of the photoluminescence of silver nanoclusters and
nanoparticles was evaluated to be 0.09.
In terms of their small size, brightness and photostability, noble metal nanoclusters and nanoparticles hold
the most promise as candidates for biological cell imaging, competing with commonly used semiconductor quantum
dots, fluorescent proteins and organic dyes. When applied to the problem of intracellular imaging, metal
nanoclusters and small nanoparticles offer advantages over their much larger sized semiconductor counterparts in
terms of ease of biological delivery. In addition, noble metal nanoparticles and nanoclusters are photostable. The
high quantum yield (QY) of the photoluminescence emission signal enables the isolation of their
photoluminescence from the cellular autofluorescence in cell imaging, improving the image contrast.
In the given work the rough surface of semiconductor is modeling by 2D fractal Wierstrass function. On the basis of the Kirchhoff scalar theory the scattering indicatrices for the some types od scattering surfaces are present. On the basis of numerical accounts average scattering coefficient the diagrams of dependence for various fractal semiconductor surfaces was constructed.
The theoretical calculations of the far-IR absorption by composites with small metallic inclusions are performed. The main electrostatic assumption of electrically small inclusions in the case of high conductive particles in the far-IR range is not valid. The modified expressions for the dielectric and magnetic permeability of the metallic inclusions are obtained using Mie theory. The calculated absorption spectra of Pd-KCl composite in the far-IR region are in good agreement with experiment.
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