Tunable surface-plasmon-resonance wavelength of silver island films

This paper experimentally and theoretically investigates the effect of the underlayer medium on tuning of the surface plasmon resonance (SPR) wavelength of silver island films,and the effect of substrate temperature on the morphologies and optical properties of the films.From the absorption spectra of single Ag with various thickness and overcoated (Ag/TiO 2) films deposited on glass substrates at various substrate temperatures by RF magnetron sputtering,we demonstrate that the surface plasmon resonance wavelength can be made tunable by changing the underlayer medium,the thickness of metal layer and the substrate temperature.By varying substrate temperatures,the interparticle coupling effects on plasmon resonances of nanosilver particles enhance as the spacing between the particles reduces.When the substrate temperature is up to 500 C,the absorption peak decreases sharply and shifts to shorter wavelength side due to the severe coalescence between silver islands in the film.     

Low-frequency plasmons in coupled electronic microstructures

The plasmon spectrum and the absorption of an electromagnetic wave in an electronic two-dimensional plasma with strongly modulated density are studied. The appearance of additional plasmon modes in a system of electronic wires and islands with weak current coupling is described in a model of an electronic system covered with metallic gates. Such plasmon modes appear in the low-frequency region of the spectrum, as compared with the conventional plasma oscillations, and have recently been observed experimentally in paired wires. Fiz. Tverd. Tela (St. Petersburg) 40, 542–545 (March 1998)     

Localized surface plasmon polaritons and nonlinear overcoming of the diffraction optical limit

Experimental results on the formation of ordered structures on the surface and in the near-surface layer of condensed media under the action of linearly polarized laser radiation pulses are analyzed. The formation of subdiffraction nanostructure gratings with anomalous orientation is discussed in the context of the universal polariton model. A physical model of the formation of anomalous structure gratings with periods much less than the laser radiation wavelength is proposed and experimentally verified. The model is based on excitation and mutual interference of channel (wedge) surface plasmon polaritons.     

Surface plasmon microscopy using an energy-filtered low energy electron microscope

We present low energy electron microscope (LEEM) spectromicroscopy studies of surface plasmons, localized on micro- and nanoscale epitaxial Ag islands. Excellent agreement is found in a direct comparison of wave vector dependent plasmon intensity with theory, demonstrating that high quality quantitative data can be obtained with a large improvement in both spatial and temporal resolution over traditional electron scattering experiments. The plasmon signal from Ag islands is successfully imaged with a spatial resolution of less than 35 nm. LEEM based plasmon spectromicroscopy promises to be a powerful tool for furthering our understanding of nanoplasmonics.     

Fluctuations of local optical anisotropy of island films

A method for the determination of the island film structure parameters by measuring fluctuations of optical characteristics of small areas of the film is proposed and implemented. The extinction fluctuations of the laser beam are measured experimentally in a focal spot, in which the polarization of radiation is modulated in time and which is movable over the film. From the optical data thus obtained, the optical absorption anisotropy of the nanometer-size islands of the film is evaluated. It is shown that this characteristic has a considerable frequency dispersion in the region of plasmon resonances of the nanoparticles.     

Large-scale plasmonic-SERS templates by successive growth steps

This work presents the fabrication of large-scale tunable-plasmonic surface-enhanced Raman scattering (SERS) templates and investigates their Raman enhancement. Substrates for SERS were prepared by deposition of gold nanoparticles on a glass slide followed by their growth. A plasmon shift was observed upon growing due to the formation of elongated nanoparticles and their mutual coupling. The changes in particle size, shape and interparticle distances were indicated by SEM measurements. Surface-enhanced Raman spectra of Nile blue A at a very low concentration on top of a blocking layer were measured. The overall Raman enhancement is correlated with the number of growth steps. For excitation at 532 nm four growth steps lead to maximum enhancement. Better overlap of excitation laser and the plasmon resonances upon growing increased the enhancement until four steps while further growing decreased the enhancement. At longer wavelengths excitation (633 and 785 nm) the enhancement further increased beyond the fourth growth step. This enhancement is caused by the plasmon excitation of narrower gap sizes. The proposed procedure for the SERS substrates is simple, allows covering large surface areas and plasmon band tuning from 530 nm to the near infrared in order to increase overall Raman enhancement.     

Effect of Spectral Overlap and Separation Distance on Exciton and Biexciton Quantum Yields and Radiative and Nonradiative Recombination Rates in Quantum Dots Near Plasmon Nanoparticles

Efficient biexciton (BX) photoluminescence (PL) from quantum dots (QDs) paves the way to the generation of entangled photons and related applications. However, the quantum yield (QY) of BX PL is much lower than that for single excitons (EX) due to efficient Auger-like recombination. In the vicinity of plasmon nanoparticles, the recombination rates of EX and BX may be affected by the Purcell effect, fluorescence quenching, and the excitation rate enhancement. Here, the effect of the plasmon resonance spectral position on the EX and BX PL is experimentally studied in two cases: when the plasmon band overlaps with the excitation wavelength and when it coincides with the QDs PL band. In the first case, the EX and BX excitation efficiencies are significantly increased but the EX QY reduced. As a result, the BX-to-EX QY ratio is higher than 1 at plasmon–exciton systems separations shorter than 40 nm. In the second case, the radiative recombination rates are enhanced by several orders of magnitude, which led to an increase in BX QY over distances of up to 90 nm. Finally, these two effects are obtained in the same hybrid structure, with the resultant increase in both excitation efficiency and QY of BX PL.     

Controlling the spin polarization of nanostructures on magnetic substrates

It is shown that, by utilizing spin-selective quantum interference, the spin polarization of nanostructures deposited on a magnetic substrate with a surface state can be strongly modulated locally and energetically by an appropriate structural design. This finding is deduced from state-of-the-art ab initio calculations and interpreted within an analytical model. We present results for hexagonal Cu corrals and mesoscopic triangular Co islands on Co-covered Cu(111). These systems are experimentally feasible, and the effect should be detectable with current technology.     

Spatial structures of islands of electron-hole liquid in semiconductor quantum wells

The formation of the different structures of islands of electron-hole liquid in the quantum well is studied in a statistical model. The interaction between the islands of electron-hole liquid is considered by influencing of neighboring islands through exciton gas around the considered island. Two restricted regions were studied: an infinite strip and a disk. The theory gives the possibility to determine the probability of different states realization and to find the most probable state. The dependence of the radius, mutual positions of the electron-hole liquid islands, the number of the islands in the disk on the pumping, temperature and parameters of the system (the size and the shape) are calculated.     

The Spectrum of Thermally Stimulated Surface Plasmon Polaritons of a Linear Sample

An analytical model of the spectrum of thermally stimulated surface plasmon polaritons (TSSPPs) coming to the edge of a linear conducting sample has been developed. It has been found that the spectrum of such TSSPPs obeys neither the Wien law nor the Stefan–Boltzmann law for thermal radiation. The maximum of this spectrum is shifted to the low-frequency region with respect to the spectrum of the absolutely black body, and the magnitude of the shift is proportional to the sample length. The plasmon nature of the intensity increment of thermal radiation from the edge of a plane face of a duralumin sample has been verified experimentally. It has been shown that the intensity and spectrum of this increment can be controlled both by the sample temperature and by the extension of the face.     

Density-dependent optical response of gold nanoparticle monolayers on silicon substrates

We experimentally and theoretically study the density-dependent optical properties of 20 nm gold nanoparticle monolayers on silicon at 530 nm. Both results indicate a density-dependent resonance behavior. The density-dependent resonance suggests that the optical properties of the gold nanoparticle monolayers can be drastically modulated by changing the volume ratio V(r). It also implies, in this composite system, that the total surface plasmon resonance is maximized at a certain V(r).     

Influence of surface roughness on surface plasmon resonance phenomenon of gold film

We experimentally investigate the effects of the surface roughness of gold thin films on the properties of surface plasmon resonance. By annealing at different temperatures, film samples with different surface morphologies are obtained. Specifically, due to the diffusion of the gold atoms towards the films3 surface, the surface rootmean-square roughness decreases with the increasing annealing temperature. Then, we measure the surface plasmon resonance of the samples. The results show that the resonance angle of the surface plasmon resonance is sensitive to the root-mean-square roughness, and it gradually decreases by reducing the surface root-mean-square roughness.Yang     

Interplay of structural and temperature effects on plasmonic excitations at noble-metal interfaces

The interplay of structural and electronic properties on plasmon modes was investigated for a thin Ag film grown at room temperature on Cu(111). Surface plasmons are confined within Ag grains, as indicated by the analysis of their dispersion relationship, which is dispersionless up to a critical wave-vector. Surface plasmon confinement is removed upon annealing at 400?K. The thermal treatment induces a flattening of the Ag adlayer with a merging of Ag islands, and, moreover, a strong enhancement of surface conductivity.     

Energy loss and plasmon excitation during electron emission in the proximity of a solid surface

We study the interaction with bulk and surface modes of electrons emitted in the proximity of a solid surface. We analyze the modifications in the energy loss, and in bulk and surface plasmon excitations, taking into account the effects due to the sudden creation of the electron and residual atomic hole, and the finite distance to the surface. The process is described using the dielectric function formulation and the specular reflection model. We derive expressions for the electrostatic potential in the medium and in vacuum, which include all the terms due to bulk and surface modes. The effect of each term in the energy loss rate and in the average number of plasmon excitations is discussed. The results illustrate in detail the different spatial dependences of the electron and ion interactions with the bulk and surface perturbations, through the relevant range of distances for studies of electron emission in the proximity of solid surfaces.     

Linear response of a two-layer electron gas II

In this paper we present some new theoretical results from our study of a two-layer electron gas separated by a variable distance, based on a model recently proposed by us (referred to as the CD model) and also beyond that model. In a recent communication we derived analytical results for the optical and acoustic plasmon modes in the presence of electron impurity collisions on the layers and briefly presented an energy loss function. The present paper contains results of our further exploration of the CD model and a detailed consideration of the energy loss functions. We present plots for the loss functions and discuss the prospects of experimentally observing the elusive acoustic plasmon.     

Optical manifestations of self-diffusion of atoms over the surfaces of silver nanoparticles

The kinetics of the extinction spectrum of a thin island silver film heated in the temperature range 473–553 K is studied experimentally. The observed variations in the inhomogeneously broadened extinction spectrum are related to two types of changes in the morphology of islands, namely, (i) coalescence and fragmentation of the islands at the initial stage and (ii) subsequent rounding of individual islands. This conclusion is supported by the data of electron microscopy of the film at different stages of its heating. The long duration of the relaxation process is explained by specific features of mass transfer over the surfaces of granulated nanoparticles.     

Enlargement of the band gap in the metal-insulator-metal heterowaveguide

We present a new metal-insulator-metal (MIM) heterowaveguide to enlarge the band gap, which is formed by alternately stacking two kinds of metals, modulating the MIM waveguide slit, and inserting different dielectric materials with the effective refractive index periodically modulated. Based on this structure, we adopt two different methods to enlarge the band gap: changing the thickness of the unit layer and combining two MIM structures. Both of them widen the band gap when surface plasmon polaritons propagate through the structure. This metal heterostructure is expected to have applications in surface plasmon polaritons (SPPs) based optical devices, such as filters, waveguides, especially for broad band gap elements.     

Surface plasmon enhanced light emission of silicon-rich silicon nitride: Dependence on metal island size

Surface plasmon coupled light emission of silicon-rich silicon nitride (SRSN) was investigated as a function of metal island size. It was found that the emission intensity was enhanced by surface plasmon (SP) and the enhancement factors increase greatly with the increase of metal island size. Moreover, SP coupled emission spectral shape was found also correlating with Ag island size. By calculating the extinction characteristics of the Ag islands, it was believed that SP scattering and absorption efficiency of the metal islands decide the photoluminescence (PL) changes including emission intensity enhancement and band position shift.     

Vertical ordering of islands in Ge-Si multilayers

Growth and ordering of GeSi islands in Ge-Si multilayer systems during deposition by Low-Pressure Chemical Vapour Deposition (LPCVD) at 700°C on Si (001) substrates have been investigated for different layer distances by transmission electron microscopy of cross-section and plane-view specimens. Vertical ordering of GeSi islands with almost perfect correlation is observed for distances between the Ge layers of 100 nm. At larger interlayer distances, a continuous decrease of the correlation is found. Vertical ordering in the multilayer system is modelled in terms of the elastic interaction between island nuclei in a newly forming layer and close islands in a buried layer below. Lateral ordering parallel to < 100 >, as observed previously in larger Ge-Si multilayer systems is not found in our systems, consisting of two Ge layers. This difference indicates that lateral ordering in the upper Ge layers of a large multilayer system is triggered by vertical ordering.     

Local-field correction of the charged Bose condensate for two and three dimensions

The local-field correction for the dielectric function of the two-dimensional and of the three-dimensional Bose condensate is calculated within a sum-rule version of the Singwi et al. (Phys. Rev.176, 589 (1968)) approach. We derive analytical expressions for small and large wave numbers and give analytical expressions for the density dependence. We compare the results of the groundstate energy for the three-dimensional system with Monte-Carlo computations. In two dimensions a roton structure in the plasmon dispersion is found at low boson density. The plasmon density of states is calculated. A correlation induced charge-density-wave instability in layered structures of two-dimensional Bose gases is discussed.