Experimental evidence for strong plasmon coupling in the soft X-ray appearance potential spectrum of graphite

Plasmon satellite structure is known to be weak in X-ray absorption experiments because of the effective cancellation between the couplings to the conduction electrons of the excited electron and core hole. Data on the soft X-ray appearance potential spectrum for the K-shell excitation of graphite however are shown to exhibit strong plasmon effects illustrating the enhanced coupling that results from the creation of an additional conduction electron.     

Core hole,plasmon coupling in the soft X-ray appearance potential spectrum of graphite

A direct comparison is presented between the results of core-level characteristic loss and soft X-ray appearance potential spectroscopies for the case of K-shell excitation in graphite. The agreement between the results of these two techniques indicates that contrary to earlier suggestions, plasmon coupling to the suddenly created core hole during the excitation does not contribute appreciably to the spectral shape.     

Directional excitation of surface plasmon polaritons in structure of subwavelength metallic holes

In this paper, we propose a structure formed by two subwavelength holes fabricated in a metal film to realize directional excitation of surface plasmon polaritons (SPPs). The holes are employed as SPP sources, and the relative phase of SPPs generated at the hole exit end can be adjusted by changing the dielectric material filled in holes. Using the difference in relative phase values of SPP for two holes filled with different dielectric media, the SPPs can interfere constructively along one direction while destructively along the opposite direction. Our theoretical analysis is verified by the three-dimensional finite-difference time-domain method. Moreover, the directional excitation of SPPs in two-hole array structure is also discussed. It is found that the effect of SPPs directional excitation is improved with the increase of the number of two-hole.     

Experimental study of transmission enhancement of evanescent waves through silver films assisted by surface plasmon excitation

In this paper, we investigated an essential precursor of superlensing: enhancing the transmission of evanescent waves assisted by excitation of surface plasmon. Using natural roughness as a well characterized grating, the transmission of evanescent waves is studied through silver thin films of increasing thickness. Measurements and calculations are performed in the wavelength range of 514.5 nm to 351.1 nm where the real part of the permittivity of silver is negative. Pronounced peaks due to surface-plasmon excitations are observed in the transmission spectra. We found the transmission of evanescent waves rapidly grows with the film thickness up to about 50 nm, after which it decays as loss becomes significant. As the permittivity of a silver slab approaches -1, we experimentally observed a broadening of surface plasmon bandwidth. Our study indicates a pathway to access the deep subwavelength features by metamaterial superlens. PACS 42.79-e; 42.30.Wb; 78.20.Ci; 78.66.Bz     

A photoemission-into-electrolyte study of surface plasmon excitation on high index faces of silver

By use of photoemission-into-electrolyte spectroscopy on a cylindrical silver single crystal the optical excitation and decay of surface plasmons on high index faces of silver has been studied. After electrochemical roughening the surface plasmon excitation showed a pronounced polarization dependence. Photoemission, induced by the decay of the excited plasmon. was only detected for orientations very close to the densely packed Ag(111) face.     

Magneto-optical recording on the multilayers systems with plasmon excitation

The maximization of the sensitivity of magneto-optical recording media in the short wavelength region is discussed. We show that a combination of the optimized thickness of dielectric and Ag (or CoAg) films can increase the magneto-optic Kerr effect in FeTbCo media by about five times of magnitude in the UV and blue spectral range. It has been shown that the local plasmon excited in the Ag-based films strongly enhances the magneto-optical properties in amorphous FeTbCo magnetic film. The Kerr rotation spectra get the maxima values for the resonance conditions when the local plasmon can be excited in the Ag or CoAg films.     

Efficient directional excitation of surface plasmon polaritons by partial dielectric filling slit structure

In this paper, we investigate the excitation of surface plasmon polariton (SPP) in the metallic slit partly filled with dielectric by using the finite-difference time-domain method. It is found that the slit structure displays high asymmetry in the field distribution and SPP excitation due to the difference in matching degree of SPP wavevector on the two sides of slit exit. At certain incident wavelengths, the power flow carried by SPP modes on one side of slit exit is over three orders of magnitude greater than that on the other side, an efficient directional excitation is achieved. The SPP generation efficiencies on both sides of slit exit can be periodically adjusted by the dielectric width, but their changes are not synchronous, implying that such slit structure could be acted as a directional splitter/coupler. Moreover, the asymmetry degree of SPP excitation can also be modulated by the refractive index of dielectric layer.     

Surface plasmon excitation in field ion emission

The excitation of surface plasmons in field ion spectroscopy is studied theoretically for realistic paraboloid shapes of emitting metallic tips and for finite ionization times.     

分子激发中的表面等离激元增强效应

金属纳米粒子的表面等离激元增强效应是纳米科学领域的一个研究热点.针对染料分子与金属纳米粒子的耦合系统,应用偶极-偶极近似计算分子与金属纳米粒子的库仑相互作用,并应用密度矩阵理论描述在不同极化方向的电场作用下的电荷输运过程,分析了分子与金属纳米粒子在不同相对位置下分子激发态的动力学过程,发现表面等离激元的增强效应与分子和金属钠米粒子的相对位置以及等离激元的耗散系数有密切关系,详细讨论了分子与金属纳米粒子间的耦合强度、外场的极化方向、等离激元的寿命及共振激发条件对分子激发态及表面等离激元增强的影响,分析了分子-金属纳米粒子耦合系统中表面等离激元增强效应的物理本质.     

A multiband absorber based on multipolar plasmon excitation

We report a multiband absorber with a top-layer grating structure based on the multipolar plasmon excitation. The simulation results show that the absorber has three distinctive absorption peaks originated from multipolar plasmon excitation at wavelengths λ = 0.576 μm, λ = 0.760 μm and λ = 5.630 μm with the absorption magnitudes more than 0.86, 0.96 and 0.99, respectively. The multipolar plasmon excitation can be described by surface plasmon standing waves.     

Density effect and plasmon bremsstrahlung in the theory of plasmon excitation by large-angle scattered electrons

Experiments on plasmon excitation by electrons which scatter at large angles constitute one of the basic sources of information on plasmon in solids. These experiments provide spectra especially rich in detail, of electrons backscattered from targets having a comparatively perfect structure. Besides, these are the only experiments that are possible at low energies of incident electrons when no shooting of thin films can take place. In such experiments the lattice must absolutely be involved in the process of electron backscattering, since the plasmon cannot appreciably affect the direction of motion of electrons. However, the lattice not only causes the appearance of backscattered electrons, but can also affect the very process of plasmon excitation. In the present paper a theoretical treatment is given of the influence which the lattice exerts on the process of plasmon generation. This influence is displayed through two effects: the bremsstrahlung of plasmons and the density effect. These effects are due to the processes of either the plasmon emission beginning before the termination of the electron-lattice collision or the electron-lattice collision beginning before the termination of electron-plasmon collision event and to the interference of these processes. The most important result of the theory developed in the paper is that these effects lead to the broadening of the plasmon resonance line, which is of the same, or even greater, order of magnitude than that due to the traditional mechanisms.     

Surface plasmon assisted photoemission from Au nanoparticles on graphite

The resonant multiple excitation of collective modes in metallic nanoparticles using ultrashort laser pulses leads to an enhanced multiphoton photoemission from the particles. This effect is here demonstrated for the surface-plasmon resonance of Au nanoparticles on graphite. The shape of the photoemission spectra is explained by multiphoton photo-assisted thermionic emission from the nanoparticles and resonant emission via the image-potential state on graphite. Tuning the photon energy between 1.7 eV and 3.2 eV allows the identification of an enhancement of the photoemission yield at 2.1±0.1-eV photon energy that is attributed to the resonant excitation of the surface plasmon in the Au nanoparticles. This identification of the surface-plasmon excitation in this energy range is also supported by electron energy loss spectroscopy. Received: 8 August 2001 / Revised version: 13 September 2001 / Published online: 10 October 2001     

Nonlinear resonance-enhanced excitation of surface plasmon polaritons

We theoretically investigate nonlinear resonance-enhanced excitation of surface plasmon polaritons in a metal coated by a one-dimensional photonic crystal. Tunneling modes above the air-light line can be directly excited in this structure. Then, with suitable parameters, photon energy and momentum conservation between the tunneling mode and the surface plasmon polaritons can be realized by means of nonlinear four-wave mixing. Compared with the nonlinear excitation of surface plasmon polaritons in a bulk metal [Phys. Rev. Lett. 103, 266802 (2009)], the conversion efficiency in our structure is noticeably enhanced.     

Bulk and surface plasmon excitation in X-ray photoemission

A quantitative theory of bulk and surface plasmon excitation by X-ray photoelectrons in thin metallic films is presented. The shape and strength of inelastic peaks in energy spectra are calculated. Their dependence on the point of primary excitation, energy and direction of the outgoing electron is discussed in the case of X-ray photoemission from aluminium.     

Effect of palladium particle size on the appearance of superstructure of graphite in palladium/graphite model catalyst

Scanning tunneling microscopy images of palladium particles supported on highly oriented pyrolytic graphite as a model catalyst in ultra-high vacuum have been observed. We found superstructures on graphite lattice due to electronic interaction between palladium particles and graphite in the vicinity of small two-dimensional palladium particles (lateral size <2 nm, height <0.5 nm). However, such superstructures could not be observed near larger three-dimensional palladium particles (lateral size ∼4 nm, height ∼2 nm). The results indicate the importance of not only the size but also the dimension of metal particles in interaction between palladium and graphite, the nature of which can be interpreted by the difference in electronic properties of atomic and bulk palladium. This has important implications to the understanding of metal-support electronic interaction and its effect on the surface catalytic reactivity of supported metal catalysts.     

一维原子链局域等离激元的非线性激发

本文基于含时密度泛函理论, 研究了不同频率光脉冲场作用下一维钠原子链中电子的输运与等离激元共振之间的耦合规律. 在等离激元共振点附近约0.8 eV频率范围内的光脉冲场, 都可以激发体系的等离激元共振. 这些不同频率外场激发的等离激元共振强度大小在一个数量级. 外场频率越接近等离激元共振频率, 外场激起的等离激元振动的振幅越大. 对于线性原子链等离激元的非线性激发现象, 本文用经典谐振子模型给出了定性解释.     

X-ray diffraction study of the structure of xenon multilayers on single crystal graphite

The structures of xenon multilayers (1 to 44 layers) physisorbed onto a graphite single crystal surface have been studied using x-ray scattering techniques. Both the intra-planar and inter-planar structures could be examined by measurements of the (1 0l) diffraction rods. The (0 0l) diffraction provides direct information about the thickness of the multilayer. We find two principal and surprising results. First, the xenon does not form an infinite number of layers at low temperatures. This disagrees with a number of previous reports which suggest complete wetting of xenon on graphite. Second, the structures of the adsorbed layers turn out to be rather elaborate. Instead of uniform, defect free layers, the xenon multilayers exhibit stacking disorder and a commensurate-incommensurate transition in the first layer.     

The role of daughter nuclei excitation in a structure of photonuclear resonances

The results of microscopic calculations of dipole resonances in ³²S and ³⁴S nuclei obtained on the basis of a “particle-finite nucleus state” using the spectroscopic factors of a nucleon pick-up reaction are presented. The conditions for the applicability of this approach to obtaining a realistic picture of a photo-excitation cross section are discussed.