Scattering of surface plasmon-polaritons and volume waves by thin gold films

The specific features of elastic scattering of volume waves and surface plasmon polaritons by polycrystalline gold films have been investigated. An analysis of the relative scattered energy, power spectral density of surface roughness, and integral and angular dependences of scattering of waves of different nature indicates a strong nonradiative multiple scattering of surface plasmon polaritons in gold films. When roughness increases, this scattering leads to an increase in scattering isotropy and to a partial loss of structural information about gold films. The analysis of the scattered energy of surface plasmon polaritons with application of the data on multifractal dimension of gold surface indicates also that the radiative scattering of surface plasmon polaritons depends on both the rms surface roughness and the surface wave propagation length.     

Nuclear physics parallels in atomic cluster physics

This paper considers some examples of physical phenomena, manifesting themselves in electron scattering on atomic clusters, which are analogous with those known from nuclear physics. It is demonstrated that the electron diffraction plays an important role in the formation of both elastic and inelastic electron scattering cross sections. The essential role of the multipole plasmon excitations in the formation of electron energy loss spectra on clusters is elucidated. The main emphasis in the paper is laid on electron scattering on fullerenes and metal clusters, however, results are applicable to some extent to other types of clusters as well.     

Excitation of 2D plasmons in a Cs/W(110) system

The evolution of surface photoemission spectra was investigated for a Cs/W(110) system with metastable Cs coatings larger than a monolayer. It is demonstrated that 2D plasmons can be detected by threshold photoemission spectroscopy. Three photoemission peaks were observed, whose dependence on the Cs adsorption dose showed a complicated behavior. The peaks may be due to the photoinduced excitation of a plasmon in quasi-2D Cs clusters, a surface Cs plasmon, or an interface Cs-W plasmon.     

Electromagnetic energy flow near nanoparticles—I: single spheres

The electromagnetic (EM) energy flow near single spheres is investigated by applying Mie theory. From the patterns of the energy flow, the absorption and the scattering of light can be understood in the microscopic point of view. In the absorption profiles of metallic particles, most absorbed energy is consumed on the surface of the particles, which indicates that the resonance of surface plasmon is different from that of the bulk plasmon. Two mechanisms to enhanced local EM field are also distinguished. One is the surface plasmon resonance, and another one is the intensified energy flow.     

Structural and electronic model of negative electron affinity on the Si/Cs/O surface

Structural and electronic models are proposed which correlate Goldstein's LEED, Auger, photo-emission, plasmon, and desorption data for negative electron affinity (NEA) on Si(100) surfaces. In the structural model, the surface Si atoms group into adjacent rows of surface “pedestals” and surface “caves”. Their density is 3.4 × 10¹⁴ cm^?2 each, as inferred from the LEED 2 × 2 reconstruction pattern and other data. Adsorbed Cs resides in fourfold coordination with Si atop the pedestals. Adsorbed oxygen is completely submerged in the caves of aperture 2.98Å to give a Cs-O dipole length of 2.9Å. Similar structural arguments show why Cs must be adsorbed before O₂, and why Si(111) does not exhibit NEA. In the electronic model, the surface dielectric constant, 5.3. obtained from the surface plasmon energy, 7 eV, is used to compute the dipole length from the final work function, 0.9 eV. It is 2.8Å in excellent agreement with the dipole length computed from the above structural model. Some properties of the “induced” surface states in the presence of Cs and O are also described.     

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.     

LEED,Auger and plasmon studies of negative electron affinity on Si produced by the adsorption of Cs and O

We have made LEED, Auger, and Plasmon measurements to study how Cs and O adsorb onto the (100) surface of p-type degenerate Si to produce negative electron affinity (NEA). A key factor to producing NEA was found to be a highly ordered Si surface as reflected by very high quality 2×2 LEED patterns. When NEA is produced, both the adsorbed Cs and O give the same LEED pattern as the original Si surface, but with a general enhancement of the half-order spot intensity. The adsorption of both Cs and O is strongly self-limiting, apparently controlled by the number of available appropriate sites on the surface. If Cs and O adsorb amorphously, NEA is not achieved. The thermal desorption of Cs occurs over a fairly broad temperature range centered at about 550°C. After Cs desorbs, the remaining O reverts spontaneously from an ordered layer to an amorphous layer, and then desorbs at about 800°C with an activation energy of 3.3 eV.Measurements of backscattered electron energy losses due to plasmons have shown that the Si surface plasmon is reduced in energy from 12.5 V to 7.0 V by the Cs-O layer. From this, an effective dielectric constant ε = 5.3 for this layer can be deduced which, in turn, enables us to characterize completely the Cs-O dipole layer.The geometrical model described by Levine for the NEA surface is consistent with our experimental results.     

Time-dependent scattering of a standing surface plasmon by rapid ionization in a semiconductor

Scattering of a standing surface plasmon by rapid ionization in a semiconductor is investigated. We show that, for a standing plasmon, in contrast with a traveling plasmon, the scattering depends on the plasmon phase at the moment of ionization. By changing the moment of ionization, we can control the energy that is transferred into newly excited modes, which include a frequency-upshifted standing surface plasmon, transient outgoing radiation, and free-streaming currents with a static magnetic field in the semiconductor. The phenomena that are described open new possibilities for probing the dynamics of surface excitations in semiconductors on an ultrashort time scale.     

Surface lattice dynamics and inelastic He scattering in Cu(111)

Summary We present a calculation of the Cu(111) surface dynamics in the framework of the multipole model. The electronic degrees of freedom include dipole and quadrupole deformabilities of the conduction electron density, the multipole expansion points being located at the midpoints between nearest-neighbour ions. The model accounts for the anomalous longitudinal resonance by an increase of dipolar deformability at the surface. Moreover the model explains in a straight-forward way the intense He scattering from the longitudinal resonance via the dipolar and quadrupolar modulations of the surface electron density. The surface dipolar contribution also explains the intense electron scattering from the optical surface resonance localized on the second layer.     

Effect of metallic surface microroughness on the probability and spectrum of plasmon excitation by a fast charged particle moving parallel to the surface

The Green’s function of the electric field of plasmons is determined in a semi-infinite medium with an abrupt plasma boundary where nonequilibrium conduction electrons either undergo elastic reflection from the boundary or “stick” to it and give rise to a stationary surface charge. The angular reflection of elastically scattered electrons can be either specular or diffuse. The Green’s function is used to find the singleevent spectrum of energy loss by a fast electron moving parallel to the boundary. The effect of electronboundary scattering parameters on the structure of bulk and surface plasmon resonances is analyzed. The probability of transition radiation of bulk plasmon by an electron moving in vacuum is examined. A new type of surface resonance is found under conditions of perfectly elastic scattering of conduction electrons from the plasma boundary, similar in structure to a tangential surface plasmon.     

Enhanced backward scattering by surface plasmons on silver film

Surface plasmon and its potential application in nanotechnology have attracted a remarkable amount of attention recently due to their novel properties. In this work we present an angularly resolved surface plasmon scattering study on a primitive metal surface. Using a reversed attenuated total reflection (RATR) setup in the experiment, we obtained a double-crescent shaped and enhanced scattering pattern at far field. The scattering pattern as a function on the variation of angle and polarization of incident beam are studied. Both theoretical and experimental results reveal an enhanced backward scattering by surface plasmon excitation. Consequently, it is shown that this angularly resolved surface plasmon scattering measurement can be employed for resolving a richness of nanoscale surface textures. PACS 42.79.-e; 42.30.Wb; 78.20.Ci     

Low-energy D scattering from Cs and CsCl adsorbed on the Si(100)2 × 1 surface

On the basis of neutralization and inelastic scattering of low-energy D⁺ ions, the bond nature of Cs and CsCl adsorbed on the Si(100)2 × 1 surface has been investigated. In a low-coverage regime ( < 0.2 ML), Cs is adsorbed ionically on Si(100) and subsequent oxygen adsorption readily causes the ionic Cs---O bond. CsCl is dissociatively adsorbed on the surface in a low-coverage regime due to the preferential reaction of Cl with the Si dangling bond and the resultant Cs is ionically bonded to Si.     

Photoassociative spectroscopy as a self-sufficient tool for the determination of the Cs triplet scattering length

In photoassociation spectroscopy, the line intensities of a given vibrational progression exhibit zero-signal modulation reflecting the node structure of the s-wave ground state wave function of two free colliding atoms. This leads to the determination of the scattering length. We performed photoassociation of cold Cs atoms polarized in the Zeeman sublevel f = 4, m(f) = 4. We analyzed the intensities of the lines associated with the Cs2 0(-)(g) state dissociating to the 6s(1/2)+6p(3/2) asymptote. This yields a value of the Cs triplet state scattering length, a(T) = -530a(0), while consistency requirements impose a value of the multipole ground state molecular coefficient, C6 = 6510 a.u.     

不同衬底银膜表面等离子激元波的辐射效率

不同衬底银膜表面等离子激元波的辐射效率邓里文王恭明（复旦大学物理系上海２００４３３）ＥｆｉｃｉｅｎｃｙｏｆＥｍｉｓｉｏｎｆｒｏｍＳｕｒｆａｃｅＰｌａｓｍｏｎＷａｖｅｓｆｏｒＤｉｆｅｒｅｎｔＳｔｒｕｃｔｕｒｅｓｏｆＡｇＦｉｌｍｓＤｅｎｇＬｉｗｅｎ，Ｗａ...     

Dynamical dipole and quadrupole response properties of small metallic particles: Random phase approximation and the modified spherical infinite barrier model

The self-consistent electrostatic response of small metallic spherical particles is studied in the random phase approximation and using the electronic wave functions in the infinite barrier model, with the size of the effective positive background adjusted to minimize the electrostatic energy of the system. The multipole susceptibilities and the numerical results are presented for the dipole (L = 1) and quadrupole (L = 2) cases. The spectra, showing both surface and several bulk plasmon peaks and the electron-hole excitations are discussed and analyzed in terms of their associated density fluctuations. The results are compared with the recent calculation of the same physical properties, based on the self-consistent field Kohn-Sham method.     

Enhancement of scattering of surface plasmon polaritons by surface defects: Technique and results

The intensities of scattering of surface plasmon polaritons by regular surface structures significantly exceed (by several orders of magnitude) the intensities of scattering of evanescent surface waves from these structures. When plasmon polaritons are scattered by diffraction grating grooves a few micrometers wide, the scattering from the trailing edge of a grating groove greatly exceeds the scattering level from the groove leading edge. Some of our original developments are presented that make it possible to put into effect an inexpensive software-hardware optical complex with a wide dynamic range, high sensitivity, and digital lock-in detection based on the use of a computer sound card.     

不同预淀积层银膜表面等离子激元波的辐射效率

测量了棱镜／ＬＢ膜／银膜／空气，棱镜／银膜／空气，棱镜／银膜／空气三种结构在衰减全反射条件下激发的表面等离子激元波由于银膜－空气界面粗糙度而散射以空气中的辐射效率，同时，由散射光强分布计算出表面度粗糙度参数随横向相关长度σ和表面波纹深度δ，再由σ和δ计算出理论辐射效率，理论与实验结果相符合。     

Emission-depth-selective auger photoelectron coincidence spectroscopy

The collision statistics of the energy dissipation of Auger and photoelectrons emitted from an amorphized Si(100) surface is studied by measuring the Si 2p photoelectron line as well as the first plasmon loss peak in coincidence with the Si-LVV Auger transition and the associated first plasmon loss. The Si 2p plasmon intensity decreases when measured in coincidence with the Si-LVV peak. If measured in coincidence with the Si-LVV plasmon the decrease is significantly smaller. The results agree quantitatively with calculations accounting for surface, volume, and intrinsic losses as well as elastic scattering in a random medium. In this way one can determine the average emission depth of individual electrons by means of Auger photoelectron coincidence spectroscopy, which therefore constitutes a unique tool to investigate interfaces at the nanoscale level.