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It is shown that correlation currents arising from the superposition of pairs of states on distinct sides of a potential barrier in metal-barrier-metal structures can result in inelastic tunneling through the emission of surface plasmons. Net gain of an externally excited plasmon field is possible.
Fukui et al. (1979) and Stegeman et al. (1982) have shown theoretically that surface plasmon polaritons can be guided over long distances by thin metal films bounded by identical dielectric media. In principle, the possibility arises for the propagation of highly localized fields. In order to obtain long propagation distances, most of the energy will have to be carried outside the metal. THis makess it necessary to operate near the mode cutoff condition. In the present investigation, it is shown that very small air gaps between the metal and dielectric surfaces will cause the mode to become radiative, and, therefore, no longer bounded to the metal film. Calculations show that gaps of dimension 100 A and less can cause severe problems in geometries relying on long range surface plasmon polaritons. High refractive index liquids placed in the gaps should alleviate these problems.
A new strategy for efficient solar-energy conversion is based on parallel processing with surface plasmons: guided electromagnetic waves supported on thin films of common metals like aluminum or silver. The approach is unique in identifying a broadband carrier with suitable range for energy transport and an inelastic tunneling process which can be used to extract more energy from the more energetic carriers without requiring different materials for each frequency band. The aim is to overcome the fundamental 56-percent loss associated with mismatch between the broad solar spectrum and the monoenergetic conduction electrons used to transport energy in conventional silicon solar cells. This paper presents a qualitative discussion of the unknowns and barrier problems, including ideas for coupling surface plasmons into the tunnels, a step which has been the weak link in the efficiency chain.
Surface plasmons on opposite sides of a thin metal film surrounded by identical dielectrics interact to form coupled surface plasmons (CSP's). Corrugation of the metal film permits interaction of the CSP's with the radiation field. This paper reports the observation of optical emission from CSP's excited by the near-field coupling of molecules adjacent to a corrugated thin metal film embedded in photoresist.
A detailed model of surface plasmon dispersion in the metal-oxide-metal tunnel diode is presented in order to clarify the spectral emission from this diode. The model predicts the location of the spectral peaks and the emission between the peaks by considering the effects of retardation on the surface plasmon. A nonradiative mode is found to play a major role in the transition from the visible to UV peaks in the diode spectra.
The Si/CoSi2/Si heterostructures prepared by codeposition and solid-phase epitaxy on Si(111) substrates were characterized using Auger plasmon data as a measure of Si overlayer thickness. The method of calibration is described, and the results of two studies, including a study of islanding in Si/CoSi2/Si and a study of diffusion in CoSi2/Si are presented, illustrating the utility of the Auger plasmon loss technique. It is shown that, most likely, the diffusion proceeds through residual defects in the CoSi2.
A surface plasmon device that operates in a transmissive mode. The light is coupled through optically transparent layers to a surface plasmon which alters the color of the light.
Biosensors of a proposed type would exploit scattering of light by surface plasmon resonance (SPR). Related prior biosensors exploit absorption of light by SPR. Relative to the prior SPR biosensors, the proposed SPR biosensors would offer greater sensitivity in some cases, enough sensitivity to detect bioparticles having dimensions as small as nanometers. A surface plasmon wave can be described as a light-induced collective oscillation in electron density at the interface between a metal and a dielectric. At SPR, most incident photons are either absorbed or scattered at the metal/dielectric interface and, consequently, reflected light is greatly attenuated. The resonance wavelength and angle of incidence depend upon the permittivities of the metal and dielectric. An SPR sensor of the type most widely used heretofore includes a gold film coated with a ligand a substance that binds analyte molecules. The gold film is thin enough to support evanescent-wave coupling through its thickness. The change in the effective index of refraction at the surface, and thus the change in the SPR response, increases with the number of bound analyte molecules. The device is illuminated at a fixed wavelength, and the intensity of light reflected from the gold surface opposite the ligand-coated surface is measured as a function of the angle of incidence. From these measurements, the angle of minimum reflection intensity is determined
We study the behavior of plasmon resonances of metal nanospheres embedded in an absorbing medium. First-principles far-field computations based on the general Lorenz–Mie theory show that increasing absorption in the host medium broadens and suppresses plasmon resonances in the extinction and effective scattering efficiency factors and suppresses resonance features in the phase function. These effects of absorption are analogous to those on the morphology-dependent resonances of dielectric particles with large size parameters.
A double-metallic deposition process is used whereby adjacent layers of different metals are deposited on a substrate. The surface plasmon frequency of a base layer of a first metal is tuned by the surface plasmon frequency of a second layer of a second metal formed thereon. The amount of tuning is dependent upon the thickness of the metallic layers, and thus tuning can be achieved by varying the thicknesses of one or both of the metallic layers. In a preferred embodiment directed to enhanced LED technology in the green spectrum regime, a double-metallic Au/Ag layer comprising a base layer of gold (Au) followed by a second layer of silver (Ag) formed thereon is deposited on top of InGaN/GaN quantum wells (QWs) on a sapphire/GaN substrate.
A method for forming a solar cell having a plasmonic back reflector is disclosed. The method includes the formation of a nanoimprinted surface on which a metal electrode is conformally disposed. The surface structure of the nanoimprinted surface gives rise to a two-dimensional pattern of nanometer-scale features in the metal electrode enabling these features to collectively form the plasmonic back reflector.
A plasmonic laser device has resonant nanocavities filled with a gain medium containing an organic dye. The resonant plasmon frequencies of the nanocavities are tuned to align with both the absorption and emission spectra of the dye. Variables in the system include the nature of the dye and the wavelength of its absorption and emission, the wavelength of the pumping radiation, and the resonance frequencies of the nanocavities. In addition the pumping frequency of the dye is selected to be close to the absorption maximum.
Here, we measured the collective plasmon scattering spectrum from diamond at pressures approaching 370 GPa. Samples are dynamically compressed employing counter-propagating laser beams where the compression states are determined by Bragg scattering. X-ray energy loss spectroscopy with 8 keV photons from the Linac Coherently Light Source (LCLS) is then applied to probe the electronic state. The x-rays excite a collective interband transition, leading to a clear plasmon signal whose dispersion matches density functional theory. The data reveal a pressure-dependent Penn gap and demonstrate a non-conducting warm dense matter state for conditions of planetary interiors.
An optical interconnect system has first and second waveguides each with wedge-shaped cross-section at a first end, disposed over an optical modulator. The optical modulator is a surface-plasmon multi quantum well (SP-MQW) modulator, the first waveguide an input waveguide and the second waveguide configured an output waveguide. In embodiments the SP-MQW modulator has multiple semiconductor layers disposed atop a lower metal layer between 10 and 300 nanometers thick and configured such that incident light is reflected at the lower metal layer unless a voltage is applied to the semiconductor layers, when incident light is coupled into a surface plasmon mode in the lower metal layer.
A central theme of nanocrystal (NC) research involves synthesis of dimension-controlled NCs and study of size-dependent scaling laws governing their optical, electrical, magnetic, and thermodynamic properties. In this paper, we describe the synthesis of monodisperse CdO NCs that exhibit high quality-factor (up to 5.5) mid-infrared (MIR) localized surface plasmon resonances (LSPR) and elucidate the inverse scaling relationship between carrier concentration and NC size. The LSPR wavelength is readily tunable between 2.4 and similar to 6.0 μm by controlling the size of CdO NCs. Structural and spectroscopic characterization provide strong evidence that free electrons primarily originate from self-doping due to NC surface-induced nonstoichiometry. The ability to probe and to control NC stoichiometry and intrinsic defects will pave the way toward predictive synthesis of doped NCs with desirable LSPR characteristics.
In this work, the application of machine learning is demonstrated for rapid and accurate extraction of plasmonic particles cluster geometries from hyperspectral image data via a dual variational autoencoder (dual-VAE). In this approach, the information is shared between the latent spaces of two VAEs acting on the particle shape data and spectral data, respectively, but enforcing a common encoding on the shape-spectra pairs. It is shown that this approach can establish the relationship between the geometric characteristics of nanoparticles and their far-field photonic responses, demonstrating that hyperspectral darkfield microscopy can be used to accurately predict the geometry (number of particles, arrangement) of a multiparticle assemblies below the diffraction limit in an automated fashion with high fidelity (for monomers (0.96), dimers (0.86), and trimers (0.58). This approach of building structure-property relationships via shared encoding is universal and should have applications to a broader range of materials science and physics problems in imaging of both molecular and nanomaterial systems.
Tip-enhanced Raman (TER) spectral images of 4-thiobenzonitrile-coated Au nanorods map the spatial profiles and trace the resonances of dipolar and multipolar plasmonic modes that are characteristic of the imaged particles. For any particular rod, we observe sequential transitions between high-order modes at low frequency shifts and lower-order modes at higher frequencies. We also notice that higher-order modes (up to $m$ = 4) are generally observed for long rods as compared to their shorter analogues, where longitudinal dipolar resonances ($m$ = 1) are observable. In effect, this research adds a new dimension to local optical field mapping via TERS, which we have previously explored. Not only can the magnitudes, vector components, local/nonlocal characters of local optical fields be imaged through molecular TERS, but spatially varying local optical resonances are also direct observables.
During the past decade, significant progress has been made in the field of resonant optics ranging from fundamental aspects to concrete applications. And while several techniques have been introduced for the fabrication of highly defined metallic nanostructures, the synthesis of complex, free-standing three-dimensional (3D) structures is still an intriguing, but so far intractable, challenge. Here, we demonstrate a 3D direct-write synthesis approach that addresses this challenge. Specifically, we succeeded in the direct-write fabrication of 3D nanoarchitectures via electron-stimulated reactions, which are applicable on virtually any material and surface morphology. Furthermore, by that, complex 3D nanostructures composed of highly compact, pure gold can be fabricated, which reveal strong plasmonic activity and pave the way for a new generation of 3D nanoplasmonic architectures that can be printed on-demand.