On surface plasmon damping in metallic nanoparticles

Two possible mechanisms of damping of surface plasmon (SP) oscillations in metallic nanoparticles (MNPs), not connected with the electron–phonon interaction, are investigated theoretically: (a) radiation damping of SPs and (b) resonant coupling of SP oscillations with electronic transitions in the matrix. For the mechanism (a) it is shown that the radiation damping rate is proportional to the number of electrons in a MNP and therefore this channel of energy outflow from the MNP becomes essential for relatively large particles. The strong frequency and size dependence of the radiation damping rate obtained allows us to separate the contributions of radiative processes and the electron–phonon interaction to the energy leakage. The investigation of the mechanism (b) shows that the rate of energy leakage of SP oscillations from a MNP does not depend on particle size and is fully determined by the optical characteristics of the matrix. It is demonstrated that for very small MNPs of -–3 5nm size, where the strong three-dimensional size quantization effect suppresses the electron–phonon interaction, the resonance coupling in certain cases provides an effective energy outflow. PACS 78.67.Bf     

Anisotropic plasmon dispersion and damping in multilayer 8-Pmmn borophene structures

We investigate the collective plasma oscillations theoretically in multilayer 8-Pmmn borophene structures, where the tilted Dirac electrons in spatially separated layers are coupled via the Coulomb interaction. We calculate the energy dispersions and Landau dampings of the multilayer plasmon excitations as a function of the total number of layers, the interlayer separation, and the different orientations. Like multilayer graphene, the plasmon spectrum in multilayer borophene consists of one in-phase optical mode and N - 1 out-of-phase acoustical modes. We show that the plasmon modes possess kinks at the boundary of the interband single-particle continuum and the apparent anisotropic behavior. All the plasmon modes approach the same dispersion at a sufficiently large interlayer spacing in the short-wavelength limit. Especially along specific orientations, the optical mode could touch an energy maximum in the nondamping region, which shows non-monotonous behavior. Our work provides an understanding of the multilayer borophene plasmon and may pave the way for multilayer borophene-based plasmonic devices.     

Sensitivity of surface plasmon resonances in spheroidal metal nanoparticles

The sensitivity of the surface plasmon resonance wavelength position in prolate and oblate metal nanoparticles to the refractive index of an embedding solution, nanoparticle shape, and temperature is studied theoretically. The influence of dissipation factor on plasmon resonance is discussed as well. The new approach specifying the optimal nanoparticle shape to reach the maximal sensitivity is proposed. The calculations are illustrated on the example of Na nanoparticle.     

Sensitivity enhancement of graphene coated surface plasmon resonance biosensor

In this paper, a highly sensitive surface plasmon resonance biosensor is presented using angular interrogation. Due to low sensitivity of conventional biosensor, graphene/two-dimensional transition metal are used in surface plasmon resonance biosensor to improve the sensitivity. Here, we propose a seven layer model of biosensor which shows by incorporating silicon layer in addition of transition metal dichalcogenides MoS₂ and graphene, the sensitivity of the proposed SPR biosensor can be greatly enhanced than the conventional gold film SPR sensors. It is observed that the highest sensitivity can be obtained by optimizing the structure with 8 nm thickness of silicon layer, one layer of MoS₂ and one layer of graphene. The highest sensitivity of our proposed sensor is 210°/RIU.     

The critical effect of the surface density gradient on surface plasmon dispersion

An analytical expression is given for the linear dispersion coefficient of surface plasmons on metals and semiconductors. The influence of the surface density profile in the selvage region is included by a model which yields a critical width.     

Dispersion and damping of a surface plasmon polariton on a one-dimensional randomly rough metal surface

Abstract

By the use of the reduced Rayleigh equation for the amplitude of a surface plasmon polariton on a one-dimensional randomly rough metal surface that is in contact with vacuum, we calculate the dispersion and damping of the surface electromagnetic wave to the lowest nonzero order in the rms height of the surface. It is found that the frequency of the surface plasmon polariton is depressed by the surface roughness. The attenuation of the surface plasmon polariton in the long wavelength limit is due primarily to its scattering into other surface plasmon polaritons, while in the short wavelength limit it is due primarily to its roughness-induced scattering into volume electromagnetic waves in the vacuum. The energy mean free path of the surface plasmon polariton is shorter on a randomly rough metal surface than it is on a lossy planar metal surface, and the surface plasmon polariton is more tightly bound to a rough surface than to a planar one.     

Ab initio results for the plasmon dispersion and damping of the warm dense electron gas

Warm dense matter (WDM) is an exotic state on the border between condensed matter and dense plasmas. Important occurrences of WDM include dense astrophysical objects, matter in the core of our Earth, and matter produced in strong compression experiments. As of late, x-ray Thomson scattering has become an advanced tool to diagnose WDM. The interpretation of the data requires model input for the dynamic structure factor S(q, ω) and the plasmon dispersion ω(q) . Recently, the first ab initio results for S(q, ω) of the homogeneous warm dense electron gas were obtained from path integral Monte Carlo simulations (Dornheim et al., Phys. Rev. Lett., 121, 255001, 2018). Here, we analyse the effects of correlations and finite temperature on the dynamic dielectric function and the plasmon dispersion. Our results for the plasmon dispersion and damping differ significantly from the random-phase approximation and from earlier models of the correlated electron gas. Moreover, we show when commonly used weak damping approximations break down and how the method of complex zeroes of the dielectric function can solve this problem for WDM conditions.     

Anomalous dispersion in nanocomposite films at the surface plasmon resonance

Nanocomposite thin films formed by Cu nanocrystals (NCs) embedded in an amorphous aluminium oxide (Al₂O₃) host have been prepared by alternate pulsed laser deposition. Spectroscopic ellipsometry is used to determine the effective refractive index (n=n+ik). The extinction coefficient is non-negligible and shows a broad absorption band related to the surface plasmon resonance. In the neighbourhood of this wavelength, the real part of the refractive index undergoes an anomalous dispersion, leading to a significant increase of the n value of the composite compared to that of the host. When the Cu content is low enough, about 2 at. %, the use of an effective medium approach combined with a regression method allows us to determine the metal content and film thickness from the ellipsometric measurements. For larger concentrations this approach is no longer valid. Received: 31 July 2001 / Revised version: 21 September 2001 / Published online: 15 October 2001     

Surface plasmon damping due to rough boundary scattering

The surface plasmon damping due to carriers scattering at the statistically rough (semiconductor-dialectric) interface is considered. The specular parameter and the integral relation are used as the boundary condition for a non-equilibrium part of the distribution function. There exist certain cases when the rough surface scattering of carriers is shown to play an important role in the surface plasmon damping.     

Sensitivity enhanced all-optical switching using prism-grating coupled surface plasmon modes

A sensitivity enhanced all-optical-switch design using prism-sinusoidal grating coupled surface plasmon modes is demonstrated numerically. Owing to the simultaneous excitation of surface plasmons for the pump and signal at the interface between a nonlinear waveguide layer and a metal layer, a sensitivity enhanced bistability effect in the structure can be obtained. The nonlinear refractive index of the waveguide layer experiences an abrupt change of the local pump field owing to this bistability effect. Such a characteristic greatly improves the performance of optical switch by reducing the threshold pump intensity. An all-optical-switch design with a pump threshold as low as 0.9 GW/cm² is presented.     

Reciprocity sum rule for metal surfaces and its application to the problem of surface plasmon dispersion

Sum rule of a new type is obtained. On this base a simple model of metal with modulated jellium background is studied. Linear optical characteristics of surface are found to differ essentially from standard uniform-jellium model. Positive surface-plasmon dispersion law on Ag is qualitatively explained.     

Nonlinear dispersion relation for surface plasmon at a metal-Kerr medium interface

The dispersion relation for the plasmon at the interface of a metal and a nonlinear Kerr medium is studied by applying a semi-analytic theory established in the literature. Explicit analytical results are obtained and are compared to those from a certain approximate treatment appeared in the literature. It is found that for large electric field strengths, both the dispersion relation and the surface plasmon frequency from the approximate treatment deviate significantly from those obtained in the exact approach, especially for the case with a negative Kerr susceptibility.     

Sensitivity improvement of aluminum-based far-ultraviolet nearly guided-wave surface plasmon resonance sensor

An aluminum (Al) based nearly guided-wave surface plasmon resonance (NGWSPR) sensor is investigated in the far-ultraviolet (FUV) region. By simultaneously optimizing the thickness of Al and dielectric films, the sensitivity of the optimized Al-based FUV-NGWSPR sensor increases from 183°/RIU to 309°/RIU, and its figure of merit rises from 26.47 RIU^-1 to 32.59 RIU^-1 when the refractive index of dielectric increases from 2 to 5. Compared with a traditional FUV-SPR sensor without dielectric, the optimized FUV-NGWSPR sensor can realize simultaneous improvement of sensitivity and figure of merit. In addition, the FUV-NGWSPR sensor with realistic materials (diamond, Ta₂O₅, and GaN) is also investigated, and 137.84%, 52.70%, and 41.89% sensitivity improvements are achieved respectively. This work proposes a method for performance improvement of FUV-SPR sensors by exciting nearly guided-wave, and could be helpful for the high-performance SPR sensor in the short-wavelength region.     

Sensitivity enhancement of surface plasmon resonance sensors through planar metallic film closely coupled to nanogratings

We investigate the sensitivity enhancement of surface plasmon resonance (SPR) sensors through planar metallic film closely coupled to nanogratings.     

Sensitivity enhancement of surface plasmon resonance sensor using continuous film metallic gratings

A surface plasmon resonance (SPR) sensor based on continuous film metallic gratings is numerically investigated for enhance sensitivity. The results calculated by rigorous coupled-wave analysis (RCWA) present that interplays between localized surface plasmons and surface plasmons polaritons contribute to sensitivity enhancement. The sensitivity enhancement factor (SEF), which represents the influence of metallic grating, increased as the grating period decreased. In addition, several reflection dips can be achieved as the period of metallic grating increased. By double-dips method, the sensitivity SPR sensor based on continuous film grating-based is improved into 153.23°/RIU, which is more sensitive than conventional thin film-based SPR sensor in the same condition. The SPR sensor based on continuous film metallic gratings exhibits good linearity.     

金属和Kerr非线性介质界面上表面等离子体激元的色散关系

从麦克斯韦方程组出发,结合边界条件,分别得到TM波和TE波在金属和Kerr非线性介质界面上表面等离子体激元的色散关系.由于非线性的存在,TM波的色散关系变得复杂,与光强、非线性系数有关.和线性情况一样,此界面不存在TE波.