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At least 793 records · Page 44

Localised plasmons in sphere-like fullerenes and nanoparticles with conducting shells: Classical electrodynamic approach

Based on the classical electrodynamic approach, we consider localised plasmons in fullerenes and small particles with metal layers and shells. At low energies of the radiation quantum, models of fullerenes as conducting shells are used taking into account the contribution of only π electrons, and at high energies, of both π and σ electrons. The obtained maxima of the scattering cross sections correspond to the values of 20 and 27 eV that were determined experimentally and in quantum models for the maxima of the photoionisation cross sections of fullerenes C{sub 60} and C{sub 28}, respectively. Approximate analytical results are presented for resonant frequencies, Q factors, radiation patterns, scattering and absorption cross sections for sphere-like particles and fullerenes, as well as integral equations and functionals for dielectric particles with a conducting shell of arbitrary shape. Analysis relies on the use of effective surface conductivity. (plasmons)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Design principles for photonic crystals based on plasmonic nanoparticle superlattices

Significance In this article, we derive a set of design principles for making photonic crystals with desired photonic stopband properties by taking advantage of spacer group, a design parameter enabled by recent advances in bottom-up assembly processes. The concept of spacer groups is experimentally realized through DNA-programmable assembly of Au nanoparticles, showing that highly reflective structures can be generated with cubic lattices and flexible spacer groups that can enable lighter and more compact 3D photonic crystals with precisely designed and even reconfigurable photonic properties. It also allows one to explore the combined effects of both photonic bandgap and the plasmonic properties of NPs, which may prove useful in fields spanning plasmonic cavity structures, optical nanocircuits, subwavelength imaging, and low-loss metamaterials.

36 MATERIALS SCIENCE↗

Surface plasmon enhanced fast electron emission from metallised fibre optic nanotips

Physical mechanisms of electron emission from fibre optic nanotips, namely, tunnelling, multi-photon, and thermionic emission, either prevent fast switching or require intense laser fields. Time-resolved electron emission from nano-sized sources finds applications ranging from material characterisation to fundamental studies of quantum coherence. We present a nano-sized electron source capable of fast-switching (≤1 ns) that can be driven with low-power femtosecond lasers. The physical mechanism that can explain emission at low laser power is surface plasmon enhanced above-threshold photoemission. An electron emission peak is observed and provides support for resonant plasmonic excitation. The electron source is a metal-coated optical fibre tapered into a nano-sized tip. The fibre is flexible and back illuminated facilitating ease of positioning. The source operates with a few nJ per laser pulse, making this a versatile emitter that enables nanometrology, multisource electron-lithography and scanning probe microscopy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Strong-field ionization of plasmonic nanoparticles

We modeled strong-field ionization of metal nanoparticles by intense infrared laser pulses, accounting for and distinguishing in photoelectron (PE) momentum distributions the effects of PE correlation, PE–residual-charge interactions, PE rescattering and recombination, and transient laser-induced plasmonic fields. Our numerical results for 5-, 30-, and 70-nm-diameter gold nanospheres and peak laser-pulse intensities of 8.0×10 12 and 1.2×10 13 W/cm 2 show how PE velocity-map images are distinctly shaped by PE Coulomb repulsion, residual-charge accumulations, and plasmonic near fields. In contrast to gaseous atomic targets and dielectric nanoparticles, we find very large PE cutoff energies, for both directly emitted and rescattered PEs, that exceed the incident laser-pulse ponderomotive energy by two orders of magnitude.

74 ATOMIC AND MOLECULAR PHYSICS↗

Thermal transfer enhancement by hydrodynamic plasmons in electron bilayers

Here, we develop a theory of heat transfer induced by thermal charge fluctuations in two-dimensional electron double layers. We consider pristine systems comprised of identical layers and focus on the regime of sufficiently high temperatures and interlayer distances 𝑑, where the relevant charge fluctuations may be described using the hydrodynamic approach. In this limit heat transfer is dominated by the plasmon resonances. For systems with Galilean-invariant electron dispersion the interlayer thermal conductance 𝜘 is proportional to the kinematic viscosity of the electron liquid and decreases as 1/𝑑 4 . In the absence of Galilean invariance 𝜘∝𝜎/𝑑 3 , where 𝜎 is the intrinsic conductivity of the liquid. This strong enhancement can be traced to a drastically different broadening of plasmon resonances in systems with and without Galilean invariance.

2-dimensional systems↗

Nonlinear Plasmonic Photoelectron Response of Ag(111)

Photons can excite collective and single-particle excitations in metals; the collective plasmonic excitations are of keen interest in physics, chemistry, optics, and nanotechnology because they enhance coupling of electromagnetic energy and can drive nonlinear processes in electronic materials, particularly where their dielectric function ϵ(ω) approaches zero. Here, we investigate the nonlinear angle-resolved two-photon photoemission (2PP) spectroscopy of the Ag(111) surface through the ϵ(ω) near-zero region. In addition to the Einsteinian single-particle photoemission, the 2PP spectra report unequivocal signatures of nonlocal dielectric, plasmonically enhanced, excitation processes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Near-Field Spectroscopy and Imaging of Subwavelength Plasmonic Terahertz Resonators

We describe the temporal evolution of the terahertz (THz) field leading to the excitation of plasmonic resonances in carbon microfibers. The field evolution is mapped in space and time for the 3/2 wavelength resonance using a subwavelength aperture THz near-field probe with an embedded THz photoconductive detector. The excitation of surface waves at the fiber tips leads to the formation of a standing wave along the fiber. Local THz time-domain spectroscopy at one of the standing wave crests shows a clear third-order resonance peak at 1.65 THz, well described by the Lorentz model. Lastly, this application of the subwavelength aperture THz near-field microscopy for mode mapping and local spectroscopy demonstrates the potential of near-field methods for studies of subwavelength plasmonic THz resonators.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Integrating Plasmonic Metals and 2D Transition Metal Dichalcogenides for Enhanced Nonlinear Frequency Conversion

Surface plasmon resonant nanoantennas can confine incident energy onto two-dimensional (2D) transition metal dichalcogenides (TMD) to enhance efficiency of harmonic conversion to higher energies, which is otherwise limited by the intrinsic A-scale interaction length. Second harmonic generation (SHG) from nanoantenna-decorated 2D TMD was heuristically examined with hyper Rayleigh scattering (HRS), multi-photon microscopy, electron energy loss spectroscopy (EELS), and discrete dipole computation. HRS experimentally quantified the frequency dependence of the second-order nonlinear susceptibility, x(2), for liquid-exfoliated WS2. Measured x(2) fell within 21% of independent density functional theory (DFT) calculations, overcoming the known 100-1000x overestimation of microscopy approaches. EELS supported design of nanoantennas for integration with TMD. Overall SHG conversion efficiencies from chemical vapor-deposited (CVD) 4x105 nm2 MoS2 crystals on silicon dioxide were enhanced up to 0.025 % W-1 in the presence of by single 150 nm Au nanoshell monomers and dimers, ostensibly due to augmented local plasmonic fields.

2D materials↗

The Spectrum of Thermally Stimulated Surface Plasmon Polaritons of a Linear Sample

An analytical model of the spectrum of thermally stimulated surface plasmon polaritons (TSSPPs) coming to the edge of a linear conducting sample has been developed. It has been found that the spectrum of such TSSPPs obeys neither the Wien law nor the Stefan–Boltzmann law for thermal radiation. The maximum of this spectrum is shifted to the low-frequency region with respect to the spectrum of the absolutely black body, and the magnitude of the shift is proportional to the sample length. The plasmon nature of the intensity increment of thermal radiation from the edge of a plane face of a duralumin sample has been verified experimentally. It has been shown that the intensity and spectrum of this increment can be controlled both by the sample temperature and by the extension of the face.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

The Shift of the Peak of a Localized Plasmon Resonance in Granulated Gold Films on the Surface of a-C:H

Spectra of optical density of granulated 2-nm-thick gold films deposited on the surface of thin films of amorphous hydrogenated carbon (a-C:H) on quartz substrates are investigated. A shift of the peak corresponding to the localized surface plasmon resonance toward the shorter wavelengths by 32 nm upon an increase in the optical bandgap of the a-C:H films from 0.8 to 2.4 eV is demonstrated. Simultaneously, an increase in intensity and narrowing of the plasmon-resonance band in spectra of gold nanostructures is observed. This fact indicates that formation of the granulated gold films on the surface of a-C:H films depends on the specific structural properties of the latter.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Energy Exchange Dynamics and Relaxation of Excitations upon Strong Exciton–Plasmon Interaction in a Planar Nanostructure of Molecular J-Aggregates on a Metal Substrate

The kinetics of energy exchange between the plasmonic and excitonic subsystems in a “metal–dielectric–molecular layer” is studied for a planar composite nanostructure with a strong exciton–plasmon interaction. It is shown that the time dependence of the energy transfer between the components of the system has the character of damped oscillations, which depend on the prepared initial state, a number of relaxation parameters, the Rabi frequency, and the detuning from resonance.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

On a new scenario for the saturation of the low-threshold two-plasmon parametric decay instability of an extraordinary wave in the inhomogeneous plasma of magnetic traps

The most probable scenario for the saturation of the low-threshold two-plasmon parametric decay instability of an electron cyclotron extraordinary wave has been analyzed. Within this scenario two upperhybrid plasmons at frequencies close to half the pump wave frequency radially trapped in the vicinity of the local maximum of the plasma density profile are excited due to the excitation of primary instability. The primary instability saturation results from the decays of the daughter upper-hybrid waves into secondary upperhybrid waves that are also radially trapped in the vicinity of the local maximum of the plasma density profile and ion Bernstein waves.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Formation of plasmon pulses in the cooperative decay of excitons of quantum dots near a metal surface

The formation of pulses of surface electromagnetic waves at a metal–dielectric boundary is considered in the process of cooperative decay of excitons of quantum dots distributed near a metal surface in a dielectric layer. It is shown that the efficiency of exciton energy transfer to excited plasmons can, in principle, be increased by selecting the dielectric material with specified values of the complex permittivity. It is found that in the mean field approximation, the semiclassical model of formation of plasmon pulses in the system under study is reduced to the pendulum equation with the additional term of nonlinear losses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Surface Plasmon Resonances of an Axially Magnetized Plasma Column in the Presence of Collisional Loss

Surface plasmon resonances arising in the course of scattering of an H-polarized plane electromagnetic wave by an axially magnetized plasma column are analyzed. Main attention is paid to the behavior of these resonances in the presence of collisional loss in the magnetoplasma filling the scatterer. The frequencies, Q factors, and amplitude coefficients of the electromagnetic field of multipole surface plasmon resonances of different orders are found, and conditions under which the collisional loss in the plasma completely suppresses a given resonance are determined.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Ultra-broadband near-field antenna for terahertz plasmonic applications

A new type of ultra-broadband near-field antenna for terahertz frequencies is proposed. This antenna is a short-period planar metal array. It is theoretically shown that irradiation of the short-period array antenna by a plane homogeneous terahertz waves excite a highly inhomogeneous near electric field near the metal array. In this case, the amplitude of the excited inhomogeneous near electric field is almost independent of frequency in the entire terahertz frequency range. The excitation of plasma oscillations in a two-dimensional electron system using the antenna under study is numerically simulated in the resonant and non-resonant plasmonic response modes. This type of antenna can be used for developing ultra-broadband plasmonic detectors of terahertz radiation.

36 MATERIALS SCIENCE↗

Surface plasmon polaritons in a composite system of porous silicon and gold

A composite system of silicon quantum dots and gold particles with properties periodically changing along the surface (i.e., a system exhibiting the properties of a diffraction grating) is obtained by a one-step metal-assisted chemical etching. The spectral and angular dependences of the photoresponse for the composite system on single-crystal silicon are studied. The photoresponse peaks were observed, which behavior (the dependence on the parameters of the diffraction grating, wavelength and incidence angles of light) is attributed to the excitation of plasmon-polariton modes at the surface of the composite system with the diffraction grating. At the same time, the obtained values of the wave vectors for these modes are smaller than those calculated for plasmon polaritons excited at the interface between air and metal (gold) diffraction grating.

36 MATERIALS SCIENCE↗

Diagnostics of the efficiency of surface plasmon-polariton excitation by quantum dots via polarization measurements of the output radiation

It is demonstrated that the efficiency of surface plasmon-polariton excitation at a metal-semiconductor interface by active quantum dots can be determined from measurements of the polarization characteristics of the output radiation. Experimentally, the proposed diagnostic method is based on finding the ratio of the intensities of the output radiation with polarizations orthogonal and parallel to the nanoheterostructure plane for two different distances between the quantum-dot layer and the metal-semiconductor interface. These data are then used to obtain the unknown parameters in the proposed mathematical model which makes it possible to calculate the rate of surface plasmon-polariton excitation by active quantum dots. As a result, this rate can be determined without complicated expensive equipment for fast time-resolved measurements.

36 MATERIALS SCIENCE↗

Nanoheterostructures with improved parameters for high-speed and efficient plasmon-polariton light emitting Schottky diodes

As a result of theoretical and experimental analyses, the parameters of heterostructures with InAs quantum dots in a GaAs matrix are determined, which provide the development of high-speed and efficient plasmon-polariton near-infrared light-emitting Schottky diodes based on such structures. The quantum dots should be arranged on a heavily doped (to a dopant concentration of 10{sup 19} cm{sup –3}) GaAs buffer layer and be separated from the metal by a thin (10–30 nm thick) undoped GaAs cap layer. The interface between the metal (e.g., gold) and GaAs provides the efficient scattering of surface plasmon-polaritons to ordinary photons if it contains inhomogeneities shaped as metal-filled cavities with a characteristic size of ~30 nm and a surface concentration above 10{sup 10} cm{sup –2}.

36 MATERIALS SCIENCE↗