Secondary plasmon resonance in graphene nanostructures

The plasmon characteristics of two graphene nanostructures are studied using time-dependent density functional theory (TDDFT). The absorption spectrum has two main bands, which result from π and σ + π plasmon resonances. At low energies, the Fourier transform of the induced charge density maps exhibits anomalous behavior, with a π phase change in the charge density maps in the plane of the graphene and those in the plane 0.3 ? from the graphene. The charge density fluctuations close to the plane of the graphene are much smaller than those above and beneath the graphene plane. However, this phenomenon disappears at higher energies. By analyzing the electronic properties, we may conclude that the restoring force for the plasmon in the plane of the graphene does not result from fixed positive ions, but rather the Coulomb interactions with the plasmonic oscillations away from the plane of the graphene, which extend in the surface-normal direction. The collective oscillation in the graphene plane results in a forced vibration. Accordingly, the low-energy plasmon in the graphene can be split into two components: a normal component, which corresponds to direct feedback of the external perturbation, and a secondary component, which corresponds to feedback of the Coulombic interaction with the normal component.     

Double plasmon resonance in spherical metal-dielectric-metal nanostructures

Results are presented from numerical simulations of the optical properties of spherical nanostructures consisting of a metal core and two shells—dielectric and metal. A study is made of nanostructures with Ag, Al, and Cu cores and an outer Ag shell. It is shown that, for certain ratios between the radii of the structure components, the plasmon resonance of the metal core and that of the metal shell can occur at the same spectral position, with resulting increases in the local electromagnetic field amplitude within the nanostructure by a factor of 10³–10⁴ and in the absorption cross section by a factor of up to 10³.     

Effect of surface roughness on surface plasmon resonance absorption

The absorption of light by surface plasmons has been studied using the method of attenuated total reflection. The reflectance from a quartz-Ag interface has been measured as a function of angle and surface structure for the wavelength region from 3600 to 6000 . It is shown that the reflectance minimum for a smooth Ag film is changed in both angular position and spectral half-width by roughening the Ag surface with CaF₂ underlayers. Dispersion curves are presented which show that the wave vector of a surface plasmon propagating on an irregular surface is greater than that of an equally energetic surface plasmon propagating on a planar surface.     

Broadband light absorption using a multilayered gap surface plasmon resonator

A broadband visible light absorber composed of multiple metal-dielectric-metal (MMDM) layers is proposed and numerically investigated. Dielectric layers of different thicknesses in the MMDM structure lead to multiple plasmon resonances at different wavelengths; as a result, efficient broadband absorption can be achieved under optimized conditions. We found that an average simulated absorption of 93 % was obtained over the entire visible spectrum of 400–700 nm by controlling the geometric parameters. Furthermore, the origin of the broadband absorption was studied, and the effects of the diameter and pitch of the pattern on the absorption were investigated. Our proposed structure with a periodic array of circular patterns represents a novel candidate for future applications in photovoltaic cells and thermal emitters.     

如何用光波激发金属表面等离体子振荡

通过求解金属表面的麦克斯韦方程,证明了光波不能直接激发表面等离体子波．介绍了Otto装置和Kretschmann装置,这两种装置可利用光波全反射时产生的倏逝波激发表面等离体子波,给出了这两种装置中棱镜和介质的相对电容率关系以及对中间层厚度的要求．     

Diagnostics of plasmon resonance in optical absorption spectra of nanographite aqueous suspensions

A characteristic feature near ～255 nm has been revealed in the optical absorption spectra of nano-graphite aqueous suspensions. This is a broad absorption peak, which is due to the surface plasmon resonance in nanographite particles. The peak shape and intensity depend on the structural quality and aggregate state of onion-like nanographite particles in suspension.     

Interplay of plasmon resonances in binary nanostructures

By introducing the difference permittivity ratio η=(ε ₂?ε ₀)/(ε ₁?ε ₀), the Green matrix method for computing surface plasmon resonances is extended to binary nanostructures. Based on the near field coupling, the interplay of plasmon resonances in two closely packed nanostrips is investigated. At a fixed wavelength, with varying η the resonances exhibit different regions: the dielectric effect region, resonance chaos region, collective resonance region, resonance flat region, and new branches region. Simultaneously, avoiding crossing and mode transfer phenomena between the resonance branches are observed. These findings will be helpful to design hybrid plasmonic subwavelength structures.     

Nonlinear absorption of light pulses under conditions of two-photon resonance in bulk crystals and nanostructures in the femtosecond pump-probe spectroscopy mode

A theory of nonlinear absorption of femtosecond light pulses by bulk crystals and nanostructures of different dimensions in the pump-probe spectroscopy mode has been developed. Expressions for the energy absorbed from the probe pulse under conditions of two-photon resonances are derived for transitions between the discrete or band electronic states and between the size-quantization subband states in quantum wells and quantum wires. The dependences of the energy absorbed from the probe pulse on the two-photon resonance detuning and on the time delay between the pulses are analyzed. The dependence of the power absorbed from the probe pulse on the time is also obtained.     

Shape-dependent plasmon resonances of Ag nanostructures

Different silver nanostructures have been rapidly synthesized under microwave irradiation from a solution of silver nitrate (AgNO₃) and β$\beta$-D glucose; neither additional reducing nor capping agent were required in this soft green solution approach. Not only spherical nanoparticles, but also necklace and wires have been synthesized. The plasmon resonances of the synthesized silver nanostructures were tuned by varying the irradiation time and hence by changing size and morphology of nanostructures. The obtained nanostructures were characterized by X-Ray diffraction (XRD), Uv–Vis spectroscopy (Uv–Vis), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The change of peak position and the shape of the absorption spectra were clearly observed during the whole reaction process; in fact, it was evidenced that initially Ag nanoparticles were formed, which, as reaction time elapsed, self-assembled and fused with each other to yield nanowires.     

Resonant light absorption and plasmon tunability of lateral triangular Au nanoprisms array

Optical characteristics and electric field distribution of triangular Au nanoprism in a unit and units array under polarized light irradiation were systematically studied by numerical simulation with finite difference time domain method. It is found that the plasmonic properties of the triangular nanoprism are dominated by the electric polarization rather than the wave propagation. The triangular nanoprism presents similar optical response with a strong dipole band under different wave propagations if the electric polarization vectors are parallel to the triangular cross section. The lateral triangular Au nanoprisms array possesses a large tunability of the plasmonic properties contributed from the combined influence of inter-particle distance, particles size, polarization angle and even environmental medium. From the plasmon band shift versus the refractive index, ultra-high local surface plasmon resonance sensitivity (509.96 nm/RIU, figure of $\text{merit}=5.55$) is reached at $\sim 850\text{nm}$, making this array promising for biochemical sensing applications.     

Enhanced light absorption of silicon in the near-infrared band by designed gold nanostructures

A scheme to enhance near-infrared band absorption of a Si nanoparticle by placing the Si nanoparticle into a designed gold nanostructure is proposed. Three-dimensional （3D） finite-difference time-domain simulations are employed to calcu- late the absorption spectrum of the Si nanostructure and maximize it by generating alternate designs. The results show that in the near-infrared region over 700 nm, the absorption of a pure Si nanoparticle is very low, but when the same nanoparticle is placed within an optimally designed gold nanostructure, its absorption cross section can be enhanced by more than two orders of magnitude in the near-infrared band.     

Efficient use of the surface plasmon polariton resonance in light scattering from adsorbates

Efficient collection of the scattered light from adsorbates on silver in the attenuated total reflection configuration is demonstrated with a so-called Weierstrass prism. The Raman signal from carbon contamination on silver films is enhanced by two orders of magnitude with respect to the simple external backscattering configuration.     

Inversion of absorption and scattering at plasmon resonance in nanoparticles with a metallic sheath

Numerical simulation of the optical properties of spherical nanostructures comprising an absorbing (amplifying) insulating core and a metallic sheath is carried out under the conditions of plasmon resonance. A decrease in the absorption by the core is shown to increase the cross sections of absorption and scattering by the nanostructure in the plasmon resonance spectral range. If the core exhibits amplification, an extra resonance arises, causing a change in the dependence of the absorption cross section on the amplification factor. Conditions for such a resonance to appear are considered.     

Total dissolved solids estimation with a fiber optic sensor of surface plasmon resonance

In this paper, surface plasmon spectra of ion influence was investigated by using a fabricated fiber optic sensors, then spectrum subtraction of ion and non-ionic solutions were developed for field applications of total dissolved solids (TDS) estimation. We confirmed the SPR spectral difference between seven ionic and three non-ionic liquid samples, that for the same refractive index, resonance wavelength in SPR spectrum is much higher for ionic samples than that in the case of non-ionic ones due to the ions influence. The positive correlation of ion content and extra resonance wavelength shift has been established for TDS estimation in water. With three groups of water samples investigation and field testing, the proposed SPR technique showed a good performance comparable to the conductivity method.     

金属表面等离体子振荡

深入浅出地分析了金属表面等离体子振荡形成的机理，利用拉普拉斯方程得到了半无限金属、金属薄膜和球状纳米金属颗粒的表面等离体子振荡频率。     

A localized surface plasmon resonance and light confinement‐enhanced near‐infrared light photodetector

Light manipulation is paramountly important to the fabrication of high‐performance optoelectronic devices such as solar cells and photodetectors. In this study, a high‐performance near‐infrared light nanophotodetector (NIRPD) was fabricated based on a germanium nanoneedles array (GeNNs array) with strong light confining capability, and single‐layer graphene (SLG) modified with heavily doped indium tin oxide nanoparticles (ITONPs), which were capable of inducing localized surface plasmon resonance (LSPR) under NIR irradiation. An optoelectronic study shows that after modification with ITONPs the device performance including photocurrent, responsivity and detectivity was considerably improved. In addition, the ITONPs@SLG/GeNNs array NIRPD was able to monitor fast‐switching optical signals, the frequency was as high as 1 MHz, with very fast response rates. Theoretical simulations based on finite‐element method (FEM) revealed that the observed high performance was not only due to the strong light‐confining capability of the GeNNs array, but also due to the plasmonic ITONPs‐induced hot electron injection. The above results suggest that the present NIRPD will have great potential in future optoelectronic devices application.

     

Polarization-independent on-axis light coupler for surface plasmon resonance using a concentric chirped grating

A novel on-axis one-element polarization-independent light in- and out-coupling mechanism for surface plasmon resonance (SPR) is proposed. The system utilizes an integrated high-NA concentric chirped grating to both focus the incident light on the metallic film and collimate the reflected beam onto a CCD array to extract the SPR signal. With NA up to 1.47, a broad sensing dynamic range from n=1 to 1.35 can be achieved. An analytical model is implemented to demonstrate the dependency of the radial location of the resonances on the detecting substance and its sensitivity to the change of the refractive index. The model shows a trend similar to rigorous ray-tracing calculations.     

Total nuclear photon absorption cross sections for some light elements

Absolute nuclear photon absorption cross sections have been measured for the elements Li, Be, C, O, Al, Si and Ca from 10 MeV up to photon energies beyond the meson production threshold. Magnetic Compton spectrometers and a bremsstrahlung spectrum with fixed end-point energy were used. The cross sections show structure in the region of the giant resonance and fall off smoothly towards higher energies. In the giant resonance region recent 1p-1h calculations are in poor agreement with these measurements except for one calculation for carbon, which included low lying excited states of the residual mass-11 system. The cross section in the intermediate region (40 to 140 MeV) can be described by the quasideuteron model with the density of deuteron-like structures taken as 8 NZ/A. The moments of the measured cross sections are compared with sum rule predictions. The integrated cross sections from 10 MeV up to the meson production threshold (140 MeV) exceed the classical dipole sum by a factor of 1.4 to 2.     

“Red shift” of the surface plasmon resonance absorption by fine metal particles

The plasma resonance absorption of fine metal particles was found by Smithard et al. to shift to longer wavelengths with decreasing particle size.We propose here a hydrodynamic model that allows us to explain this phenomenon in terms of the diffuseness of the metal particle surface. Some new data are also presented, that agree with the findings of Smithard et al.     

Low-field magnetic resonance in granular nanostructures

A series of (CoFeB) + (SiO₂) magnetic film samples was investigated by ferromagnetic resonance. The magnetic resonance in low fields was experimentally observed. The influence on the position and width of the low-field peak of the magnetic phase concentration in nanofilms and of the registration parameters of a spectrum were established.