Surface Plasma Oscillations Research Articles

WAKE EXCITATION OF PLASMA AND ELECTROMAGNETIC OSCILLATIONS BY A RELATIVISTIC ELECTRON BUNCH IN A PLASMA RESONATOR

The process of the excitation of plasma and electromagnetic oscillations by a relativistic electron bunch in a plasma resonator is considered. It is shown that the potential electric field of plasma oscillations contains the field of a bulk wake plasma wave and the fields of two surface plasma oscillations. Surface plasma oscillations are localized in the vicinity of the input and output ends of the plasma resonator. In a plasma resonator, as a result of the effect of transition radiation at the ends of the resonator, the electron bunch will also excite eigen electromagnetic oscillations of the resonator. The spatio-temporal structure of the electromagnetic field of these oscillations has been studied.

Synthesis and Near-Field Enhancement of Composite Nanoarrays Based on Electrodeposition and in Situ Reaction

Since the morphology and element composition of metal nanostructures strongly affect the surface plasma oscillation characteristics, it has been widely concerned in surface enhanced Raman scattering (SERS). Herein, we proposed a novel route to fabricate composite Au/Ag nanoparticle arrays with synergistic effect for electromagnetic enhancement. Ag nanoparticles were electrodeposited onto a home-made template with highly ordered bowl-like pits. After a novel method of “confined annealing”, we further achieved well-regulated spherical Ag NP arrays, and the composite Au/Ag nanoparticle arrays were finally obtained via in situ replacement. The fabricated composite nanostructures showed stable and sensitive surface enhanced Raman scattering (SERS) performance mainly due to the synergistic effect and abundant “hot spots”, with the enhancement factor (EF) of [Formula: see text] for crystal violet (CV) molecules. In addition, this simple and effective preparation process greatly improved the uniformity of three-dimensional nanostructures, providing a new idea for further improving the stability of SERS signals.

Ag-Ni bimetallic film on CaF2 prism for high sensitive surface plasmon resonance sensor

Ag-Ni bimetallic film on CaF2 prism for high sensitive surface plasmon resonance sensor

High-Harmonic Generation and Spin-Orbit Interaction of Light in a Relativistic Oscillating Window.

When a high power laser beam irradiates a small aperture on a solid foil target, the strong laser field drives surface plasma oscillation at the periphery of this aperture, which acts as a "relativistic oscillating window." The diffracted light that travels though such an aperture contains high-harmonics of the fundamental laser frequency. When the driving laser beam is circularly polarized, the high-harmonic generation (HHG) process facilitates a conversion of the spin angular momentum of the fundamental light into the intrinsic orbital angular momentum of the harmonics. By means of theoretical modeling and fully 3D particle-in-cell simulations, it is shown the harmonic beams of order n are optical vortices with topological charge |l|=n-1, and a power-law spectrum I_{n}∝n^{-3.5} is produced for sufficiently intense laser beams, where I_{n} is the intensity of the nth harmonic. This work opens up a new realm of possibilities for producing intense extreme ultraviolet vortices, and diffraction-based HHG studies at relativistic intensities.

Pre-equilibrium stopping and charge capture in proton-irradiated aluminum sheets

We present a first-principles study of pre-equilibrium stopping power and projectile charge capture in thin aluminum sheets irradiated by 6 - 60 keV protons. Our time-dependent density functional theory calculations reveal enhanced stopping power compared to bulk aluminum, particularly near the entrance layers. We propose the additional excitation channel of surface plasma oscillations as the most plausible explanation for this behavior. We also introduce a novel technique to compute the orbital-resolved charge state of a proton projectile after transmission through the sheet. Our results provide insight into the dynamics of orbital occupations after the projectile exits the aluminum sheet and have important implications for advancing radiation hardness and focused-ion beam techniques, especially for few-layer materials.

Theoretical Explanation of the Effect of a Decrease in the Si(111) Plasmon Energy during the Implantation of Ions with a Large Dose

Theoretical explanation of the experimentally discovered effect of a decrease in the excitation energy of surface and volume plasma oscillations of valence Si (111) electrons during the implantation of Ba and alkaline-element ions with a large dose of D > 1016 cm–2 is presented in this paper. On the basis of a two-fluid model of the electron gas, the observed effect of a decrease in the Si(111) plasmon energy is explained by the strong damping of valence electron oscillations because of disordering of the Si(111) crystal structure up to full amorphization.

Accounting for the Local Field When Determining the Dielectric Loss Spectra of Metals in the Region of the Frequencies of Volume, Surface and Localized Plasmon Oscillations.

The optical constant of bulk metal is used to determine the dispersion of the local field under one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) confinement. 3D confinement, expressed as , corresponds to the dielectric loss spectra of spherical particles with a diameter, d, much less than the wavelength of the beam used to measure the spectrum (d << λ). Excellent agreement with the results of Mie theory and experimental data for solid colloids within alkali halide crystals was observed. The function expressed as allows the measurement of spectral micro-characteristics in the frequency range of the longitudinal collective motion of the free electrons. This corresponds to the spectrum of dielectric losses of bulk plasma oscillations. The function describes the spectra of the dielectric losses of surface plasma oscillations in thin metal films. It is shown that the peak positions of , and spectra for simple metals, viz. alkali metals as well as Al, Be, Mg, Ga, In, Sn and Si, are in agreement with experimental results from electron-energy-loss spectroscopy and various optical techniques.

Two-Dimensional Optical Metasurfaces: From Plasmons to Dielectrics

Metasurfaces, kinds of planar ultrathin metamaterials, are able to modify the polarization, phase, and amplitude of physical fields of optical light by designed periodic subwavelength structures, attracting great interest in recent years. Based on the different type of the material, optical metasurfaces can be separated in two categories by the materials: one is metal and the other is dielectric. Metal metasurfaces rely on the surface plasma oscillations of subwavelength metal particles. Nevertheless, the loss caused by the metal structures has been a trouble, especially for devices working in transmit modes. The dielectric metasurfaces are based on the Faraday-Tyndall scattering of high-index dielectric light scattering particles. By reasonably designing the relevant parameters of the unit structure such as the size, direction, and shape, different functions of metasurfaces can realize and bring a wide range of applications. This article focuses on the metasurface concepts such as anomalous reflections and refractions and the working principle of different types of metasurfaces. Here, we briefly review the progress in developing optical over past few years and look into the near future.

Possible instability of the Fermi sea against surface plasma oscillations

We derive a generic formalism for studying the energy conversion processes in bounded metals. Using this formalism we show that in the collision-less limit the Fermi sea of metals should experience an instability against surface plasma oscillations, which opens for the latter an intrinsic self-amplification channel. The origin of the instability is clarified as arising from novel effects resulting from the translation symetry breaking due to the very presence of surface. The amplification rate of this channel is analytically evaluated on the basis of energy conservation and the effects of losses are discussed. In particular, the unique role played by the surface in energy conversion is unveiled. In contrast with common wisdom and in line with observations, Landau damping is shown as always overcompensated and therefore poses no serious issues in sub-wavelength plasmonics.

Radio frequency surface plasma oscillations: electrical excitation and detection by Ar/Ag(111)

We electrically excite surface plasma oscillations on a Ag(111) single crystal by alternating electric charging at radio frequency. The radio frequency signal energy of 2.2 μeV, used to induce surface plasma oscillations, is about 5 to 6 orders of magnitude lower than the plasmon energies reachable by optical excitation or electron impact. The detection of the surface plasma oscillations is achieved by nano-fabricated 2D single-crystal sensor-islands of Ar atoms, which are shown by imaging with a scanning tunneling microscope to restructure in response to the radio frequency surface plasma oscillations, providing nanometer spatial resolution and a characteristic decay time of ≈150 ns.

Surface electromagnetic wave equations in a warm magnetized quantum plasma

Based on the single-fluid plasma model, a theoretical investigation of surface electromagnetic waves in a warm quantum magnetized inhomogeneous plasma is presented. The surface electromagnetic waves are assumed to propagate on the plane between a vacuum and a warm quantum magnetized plasma. The quantum magnetohydrodynamic model includes quantum diffraction effect (Bohm potential), and quantum statistical pressure is used to derive the new dispersion relation of surface electromagnetic waves. And the general dispersion relation is analyzed in some special cases of interest. It is shown that surface plasma oscillations can be propagated due to quantum effects, and the propagation velocity is enhanced. Furthermore, the external magnetic field has a significant effect on surface wave's dispersion equation. Our work should be of a useful tool for investigating the physical characteristic of surface waves and physical properties of the bounded quantum plasmas.

Analysis of plasmonic properties of heavily doped semiconductors using full band structure calculations

Surface plasmon polaritons (SPPs) and localized surface plasmon (LSP) resonances are not limited to noble metals. Any material with a substantial amount of free carriers will support surface plasma oscillations which, when coupled to an electromagnetic field, will result in surface plasmon polaritons and localized surface plasmon resonances in confined systems. Utilizing a full band structure approach, we analyze the plasmonic properties of several heavily doped semiconductors. We present rigorous quantum mechanical calculations of the plasma frequency, and study in detail its dependence on impurity doping concentration. Results are presented for silicon, germanium, gallium arsenide, zinc oxide, and gallium nitride. For silicon and zinc oxide, the surface plasmon resonance frequency is calculated for a large range of doping concentrations and we study the dispersion of surface plasmon polaritons on thin films. The investigated properties of heavily doped semiconductors hold promises for several interesting applications within plasmonics.

Surface plasma oscillations in a thin metal film in the case of an antisymmetric magnetic field configuration

An analytical solution of the problem of description of surface plasma oscillations at an arbitrary relation between the mean free path of electrons and film thickness is obtained for thin metal films, the thickness of which does not exceed the skin layer. The case of mirror-diffusive boundary conditions is considered. The wavevector dependence of the frequency of surface plasma oscillations is derived.

Design and top-down fabrication of metallic L-shape gap nanoantennas supporting plasmon-polariton modes

In this work the design, fabrication and optical characterization of a polarization-sensitive L-shape nanoantenna device are reported. Such configuration supports plasmon-polariton modes that are combinations of in-phase and out-of-phase single antenna long-axis surface plasma oscillations. In the former case charges distributions induce in the gap region an intense hot spot while in the latter one a “zero-field spot” occurs in a plasmonic mode which can be referred to a non-zero dipolar momentum.

Optical Absorption in Overcoats of Nanoparticle Arrays on a Metallic Substrate

Surface plasma oscillations in metallic particles as well as in thin metallic films have been studied extensively in the past decades. New features regarding surface plasma excitations are, however, constantly discovered, leading, for example, to surface-enhanced Raman scattering studies and enhanced optical transmission though metal films with nanohole arrays. In the present work, the role of a metallic substrate is examined in two cases, one involving an overcoat of dielectric nanoparticles and the other an overcoat of metallic nanoparticles. Theoretical results are obtained by modeling the nanoparticles as forming a two-dimensional, hexagonal lattice of spheres. The scattered electromagnetic field is then calculated using a variant of the Green function method. Comparison with experimental results is made for nanoparticles of tungsten oxide and tin oxide deposited on either gold or silver substrates, giving qualitative agreement on the extra absorption observed when the dielectric nanoparticles are added to the metallic surfaces. Such absorption would be attributed to the mirror image effects between the particles and the substrate. On the other hand, calculations of the optical properties of silver or gold nanoparticle arrays on a gold or a silver substrate demonstrate very interesting features in the spectral region from 400 to 1,000 nm. Interactions between the nanoparticle arrays surface plasmons and their images in the metallic substrate would be responsible for the red shift observed in the absorption resonance. Moreover, effects of particle size and ambient index of refraction are studied, showing a great potential for applications in biosensing with structures consisting of metallic nanoparticle arrays on metallic substrates.

HREELS study of graphene formed on hexagonal silicon carbide

AbstractUsing high resolution electron energy loss spectroscopy (HREELS) in conjunction with low energy electron diffraction (LEED) and X‐ray induced photoelectron spectroscopy (XPS), we have studied surface reconstructions from Si‐rich to C‐rich surfaces up to graphene formation. It is shown that the coupling between the longitudinal optical phonons and the carrier plasmons that originate from the presence of the layered semimetallic character of graphene and few layer graphene (FLG) drastically influence the HREELS‐spectra. For the hydrogen smoothened SiC‐samples, which have been subsequently annealed under high Ar‐pressure [1], the Fuchs‐Kliewer surface phonon ω0 is completely screened and two other losses ω‐ and ω+, called plasmarons, appear. They originate from the coupling between surface optical phonons and plasma oscillations of free‐electrons resulting from the graphene/SiC interface. For the heated SiC‐samples under ultra‐high‐vacuum (UHV) conditions, the situation is different, which indicates cluster formation of graphene / graphite at the surface. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Electron‐phonon‐plasmon interaction in MBE‐grown indium nitride – A high resolution electron energy loss spectroscopy (HREELS) study

AbstractWe studied InN (0001) grown by plasma assisted molecular beam epitaxy (PAMBE) with high‐resolution electron energy‐loss spectroscopy (HREELS) after vacuum transfer thus avoiding any further surface preparation. We were able to detect for the first time besides the Fuchs‐Kliewer surface phonon ω0 two plasmarons ω– and ω+, which originate from the coupling between surface optical phonons ωSO and plasma oscillations of free electrons resulting from the surface accumulation layer and/or the bulk conduction band. Using dielectric theory we get new insight into the space charge regime of InN grown by MBE. We choose an approach that reaches far beyond the accumulation layer regime. Using a very wide primary beam energy regime from 1 eV up to 200 eV, the depth of information can be varied from extremely surface sensitive to bulk sensitive. Best agreement has been obtained for a downward band bending of 0.9 eV and a peak accumulation layer density of 6.5 × 1019 cm‐3 at 2 nm beneath the surface with an unintentional doping of the bulk of 1 × 1019 cm‐3. The sheet density of the ionized surface states is determined to Nss = 1.8 × 1013 cm‐2 from the self‐consistent calculation of the conduction band profile. The presented results provide important information for future InN‐based devices. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Enhanced terahertz detection by localized surface plasma oscillations in a nanoscale unipolar diode

By using a two-dimensional ensemble Monte Carlo method, we have studied the terahertz-frequency response of a self-switching device (SSD), which is a semiconductor rectifier consisting of an asymmetric nanochannel. The simulations reveal that the performance can be improved by adjusting the shape and dielectric material filling of the insulating trenches that define the SSD. We show that the rectified current of the SSD has a nonmonotonic frequency dependence with a pronounced peak occurring just below the cutoff frequency. Through optimizations of the geometry, the peak current can reach twice that at low frequencies, enabling not only a higher detection sensitivity but also a degree of frequency selectivity. The effect is discussed in terms of a localized surface plasma oscillation in the asymmetric nanostructure.

Surface plasma resonance and magneto-optical enhancement in composites containing multicore-shell structured nanoparticles

We have formulated the conditions in which dipolar surface plasma resonance is excited by light waves in composites containing nanometer-sized, $n$-fold multicore-shell structured particles (referred henceforth as ``nano-onions'') dispersed in matrices. The nano-onions have ellipsoidal shape and an arbitrary layer number $n$, which contain shell(s) (or core) of a metal having Drude type free electrons responsible for the surface plasma oscillation. By solving a quasistatic potential boundary problem in a nano-onion that is exposed to an external static electric field, we derived the effective dielectric permittivity tensor, including off-diagonal elements, for the composites, based on the Maxwell Garnett theory. The results were utilized not only to derive the resonance conditions but also to formulate the surface charge densities on the metal surfaces, from which we determined the symmetry of the dipolar surface plasmon polaritons excited in the metal shells. Calculations made on the composites containing model nano-onions of spherical shape having $n$-fold core-shell structure of sodium and a dielectric revealed the following results: (1) The surface plasmon resonance occurs at $n$ eigenfrequencies, similar to the mechanical oscillation in $n$-fold coupled oscillators; (2) at these eigenfrequencies, the composite causes resonant peaks of light extinction coefficient, and (3) the magneto-optical Kerr effect induced by a static external magnetic field is remarkably enhanced at the resonance frequencies. The magneto-optical enhancement is augmented by hypothetically reducing the dielectric loss in Na, thus increasing the quality factor $Q$ of the surface plasmon resonance. The validity limit in our calculations based on the effective medium approximation by the Maxwell Garnett theory is discussed, comparing with the calculations made by Sinzig and Quinten [Appl. Phys. A 58, 157 (1994)] based on a rigorous Mie scattering theory treatment.

Nondestructive spectroscopic method to detect MnAs metallic nanocrystals in annealed GaAs:Mn

We report an optical spectroscopic method to monitor NiAs-type MnAs (α-MnAs) nanocrystals in (Ga,Mn)As diluted magnetic semiconductors. We utilize Mn ion implantation of low temperature (LT) GaAs epitaxial thin films followed by rapid thermal annealing (RTA) to yield embedded ferromagnetic α-MnAs nanoclusters in a GaAs:Mn matrix. As-implanted samples are paramagnetic and become ferromagnetic with Curie temperature of ∼320 K after RTA at 750 °C. No peaks of potential secondary phases could be observed in x-ray diffraction measurements. However, in optical spectra, the annealed samples show resonant absorption at 0.9 eV photon energy, due to resonant surface plasma oscillation of spherical metallic phases embedded in LT GaAs. Since the absorption peak position in the photon energy has a direct relation to the value of the plasma frequency of metallic inclusions, the metallic clusters in LT GaAs are identified as α-MnAs nanocrystals by comparing them with simulations based on Maxwell–Garnett theory. We suggest that this optical method can be applied to various granular systems and diluted magnetic semiconductors as a nondestructive way to detect and quantify metallic nanoclusters.