Adiabatic description of superfocusing of femtosecond plasmon polaritons

A surface plasmon polariton is a collective oscillation of free electrons at a metal–dielectric interface. As wave phenomena, surface plasmon polaritons can be focused with the use of an appropriate excitation geometry of metal structures. In the adiabatic approximation, we demonstrate a possibility to control nanoscale short pulse superfocusing based on generation of a radially polarized surface plasmon polariton mode of a conical metal needle in view of wave reflection. The results of numerical simulations of femtosecond pulse propagation along a nanoneedle are discussed. The space–time evolution of a pulse for the near field strongly depends on a linear chirp of an initial laser pulse, which can partially compensate wave dispersion. The field distribution is calculated for different metals, chirp parameters, cone opening angles and propagation distances. The electric field near a sharp tip is described as a field of a fictitious time-dependent electric dipole located at the tip apex.     

Modulation of Cathodoluminescence by Surface Plasmons in Silver Nanowires

The waveguide modes in chemically-grown silver nanowires on silicon nitride substrates are observed using spectrally- and spatially-resolved cathodoluminescence (CL) excited by high-energy electrons in a scanning electron microscope. The presence of a long-range, travelling surface plasmon mode modulates the coupling efficiency of the incident electron energy into the nanowires, which is observed as oscillations in the measured CL with the point of excitation by the focused electron beam. The experimental data are modeled using the theory of surface plasmon polariton modes in cylindrical metal waveguides, enabling the complex mode wavenumbers and excitation strength of the long-range surface plasmon mode to be extracted. The experiments yield insight into the energy transfer mechanisms between fast electrons and coherent oscillations in surface charge density in metal nanowires and the relative amplitudes of the radiative processes excited in the wire by the electron.     

Negative photoconductivity in silver nanocubes prepared by simple photochemical method

Silver nanocubes embedded in polyvinyl alcohol matrix have been synthesised by photoirradiation technique. The composite films are characterised by FESEM, XRD, UV-Visible absorption and photoluminescence. These show characteristics of silver nanoparticles with FESEM showing the cubic shape. The photoconductivity study of these films shows decrease in photocurrent with light irradiation. Such negative photoconductivity behaviour may be attributed to dominant scattering of electrons by excited surface plasmon polaritons in nanoscale.     

石墨烯及碳纳米管实空间等离激元学的最新进展

表面等离激元是金属和掺杂半导体中光子与电子的杂化激发模式。表面等离激元的强局域电场增强效应和强限域效应可以为在亚波长尺度操控光提供新的机遇。在这篇综述中,我们将首先讨论二维石墨烯等离激元在实空间中所展示出的各种新奇物理现象的最新进展。之后我们将总结在实空间观测到的一维金属以及半导体单壁碳纳米管中的Luttinger液体等离激元。石墨烯和碳纳米管为操控等离激元响应提供了非常有前景的研究平台,同时也为探索新奇量子现象和实现纳米光电器件提供了新的可能性。     

金属表面等离子体激发的实时场分布研究

利用时域有限差分法的电磁场仿真软件建立了金属-绝缘体-金属波导结构模型,并通过持续扩展光源激发该波导结构产生表面等离子体波,研究了金属表面等离子体激发的实时场分布.结果表明,表面等离子体波的各电磁场分量可以沿着金属-绝缘体的接触面传播,但传播距离有限,且垂直于接触面向两侧指数衰减.     

Forbidden Raman scattering from acoustic plasma waves inP-typeA 3B5 semiconductors

Theoretical arguments and experimental evidence of acoustic plasmon existence in p-type A³B⁵ semiconductors are presented. The concept of the selective resonant enhancement of Raman Scattering is delivered which explains the observation of the forbidden acoustic plasmon feature. A theory of electrically screened flows of spin polarized electrons and holes is developed. Acoustic plasmon frequency is measured and the results are compared with calculated values. It is established that the scattering intensity in crossed scattering configuration is determined by a constant of spin dragging. Determination of this constant provides a valuable contribution to the theory of polarized electrons.     

High sensitivity SPR sensor for Liquid phase sample with Ag/PbS/Graphene hybrid nanostructure

A surface plasmon resonance (SPR) sensor with Ag/PbS/GR hybrid nanostructure has been proposed for the diagnostics of liquid phase samples. Here Ag/PbS/GR hybrid nanostructure is designed as an asymmetric MIM waveguide for surface plasmon. Due to the guided wave SPR (GWSPR) modes, the index of the liquid phase samples can be measured more accurately than the conventional SPR sensors. Numerical simulation results show that the sensitivity of the sensor is about 5 times higher than the conventional SPR sensors. The origin of the enhancement mechanism is the combination of GWSPR in the Ag/PbS/GR hybrid nanostructure which enables the surface plasmon to spread along the PbS layer. In Ag/PbS/GR hybrid nanostructure, the electric field is concentrated mostly in the PbS layer, and the enhancement of the field intensity is nearly 30%.     

银基透明导电多层膜界面研究进展

由于具有较低的电阻率和成本、较好的机械加工性能、设计上的灵活性,可室温沉积等优点,银基透明导电多层膜已广泛应用于低辐射膜、强电磁屏蔽、低功耗光电子器件特别是柔性电子器件等领域.但由于材料自身的性质与制备条件的差异性,实际制备的金属/电介质(或半导体)透明导电多层膜界面处往往存在表面等离子体共振、界面导电电子散射、膜层脱...     

Hybridizing Plasmonic Materials with 2D‐Transition Metal Dichalcogenides toward Functional Applications

Recently, 2D transition metal dichalcogenides (TMDs) have become intriguing materials in the versatile field of photonics and optoelectronics because of their strong light–matter interaction that stems from the atomic layer thickness, broadband optical response, controllable optoelectronic properties, and high nonlinearity, as well as compatibility. Nevertheless, the low optical cross‐section of 2D‐TMDs inhibits the light–matter interaction, resulting in lower quantum yield. Therefore, hybridizing the 2D‐TMDs with plasmonic nanomaterials has become one of the promising strategies to boost the optical absorption of thin 2D‐TMDs. The appeal of plasmonics is based on their capability to localize and enhance the electromagnetic field and increase the optical path length of light by scattering and injecting hot electrons to TMDs. In this regard, recent achievements with respect to hybridization of the plasmonic effect in 2D‐TMDs systems and its augmented optical and optoelectronic properties are reviewed. The phenomenon of plasmon‐enhanced interaction in 2D‐TMDs is briefly described and state‐of‐the‐art hybrid device applications are comprehensively discussed. Finally, an outlook on future applications of these hybrid devices is provided.     

Electron excitation in the interaction of slow ions and electrons with metals and monolayer graphite on Ni(111) surfaces

We report on the experimental energy distributions of electrons emitted in the interaction of slow ions and electrons with aluminium and with monolayer graphite deposited on a Ni(111) surface. Measurements on the Al surface clarify the role of plasmon decay in secondary electron emission. In contrast with theoretical calculations, our experiments indicate that the electron collision cascade inside the solid produced by electrons excited by plasmon decay does not contribute significantly to electron emission.The energy distribution of electrons emitted in the interaction of He⁺ ions with monolayer graphite reveal a high-energy feature that can be attributed to the autoionization decay of excitonic states populated by electron promotion in close He-C encounters.     

Reactivating Catalytic Surface: Insights into the Role of Hot Holes in Plasmonic Catalysis

Surface plasmon resonance of coinage metal nanoparticles is extensively exploited to promote catalytic reactions via harvesting solar energy. Previous efforts on elucidating the mechanisms of enhanced catalysis are devoted to hot electron‐induced photothermal conversion and direct charge transfer to the adsorbed reactants. However, little attention is paid to roles of hot holes that are generated concomitantly with hot electrons. In this work, 13 nm spherical Au nanoparticles with small absorption cross‐section are employed to catalyze a well‐studied glucose oxidation reaction. Density functional theory calculation and X‐ray absorption spectrum analysis reveal that hot holes energetically favor transferring catalytic intermediates to product molecules and then desorbing from the surface of plasmonic catalysts, resulting in the recovery of their catalytic activities. The studies shed new light on the use of the synergy of hot holes and hot electrons for plasmon‐promoted catalysis.     

Graphene plasmonics for tunable terahertz metamaterials

Plasmons describe collective oscillations of electrons. They have a fundamental role in the dynamic responses of electron systems and form the basis of research into optical metamaterials. Plasmons of two-dimensional massless electrons, as present in graphene, show unusual behaviour that enables new tunable plasmonic metamaterials and, potentially, optoelectronic applications in the terahertz frequency range. Here we explore plasmon excitations in engineered graphene micro-ribbon arrays. We demonstrate that graphene plasmon resonances can be tuned over a broad terahertz frequency range by changing micro-ribbon width and in situ electrostatic doping. The ribbon width and carrier doping dependences of graphene plasmon frequency demonstrate power-law behaviour characteristic of two-dimensional massless Dirac electrons. The plasmon resonances have remarkably large oscillator strengths, resulting in prominent room-temperature optical absorption peaks. In comparison, plasmon absorption in a conventional two-dimensional electron gas was observed only at 4.2?K (refs 13, 14). The results represent a first look at light-plasmon coupling in graphene and point to potential graphene-based terahertz metamaterials.     

Generation of traveling surface plasmon waves by free-electron impact

The injection of a beam of free 50 keV electrons into an unstructured gold surface creates a highly localized source of traveling surface plasmons with spectra centered below the surface plasmon resonance frequency. The plasmons were detected by a controlled decoupling into light with a grating at a distance from the excitation point. The dominant contribution to the plasmon generation appears to come from the recombination of d-band holes created by the electron beam excitation.     

Graphene-antenna sandwich photodetector

Nanoscale antennas sandwiched between two graphene monolayers yield a photodetector that efficiently converts visible and near-infrared photons into electrons with an 800% enhancement of the photocurrent relative to the antennaless graphene device. The antenna contributes to the photocurrent in two ways: by the transfer of hot electrons generated in the antenna structure upon plasmon decay, as well as by direct plasmon-enhanced excitation of intrinsic graphene electrons due to the antenna near field. This results in a graphene-based photodetector achieving up to 20% internal quantum efficiency in the visible and near-infrared regions of the spectrum. This device can serve as a model for merging the light-harvesting characteristics of optical frequency antennas with the highly attractive transport properties of graphene in new optoelectronic devices.     

Fluorescence Enhancement on Large Area Self‐Assembled Plasmonic‐3D Photonic Crystals

Discontinuous plasmonic‐3D photonic crystal hybrid structures are fabricated in order to evaluate the coupling effect of surface plasmon resonance and the photonic stop band. The nanostructures are prepared by silver sputtering deposition on top of hydrophobic 3D photonic crystals. The localized surface plasmon resonance of the nanostructure has a symbiotic relationship with the 3D photonic stop band, leading to highly tunable characteristics. Fluorescence enhancements of conjugated polymer and quantum dot based on these hybrid structures are studied. The maximum fluorescence enhancement for the conjugated polymer of poly(5‐methoxy‐2‐(3‐sulfopropoxy)‐1,4‐phenylenevinylene) potassium salt by a factor of 87 is achieved as compared with that on a glass substrate due to the enhanced near‐field from the discontinuous plasmonic structures, strong scattering effects from rough metal surface with photonic stop band, and accelerated decay rates from metal‐coupled excited state of the fluorophore. It is demonstrated that the enhancement induced by the hybrid structures has a larger effective distance (optimum thickness ≈130 nm) than conventional plasmonic systems. It is expected that this approach has tremendous potential in the field of sensors, fluorescence‐imaging, and optoelectronic applications.     

Extraordinary terahertz transmission through a copper film perforated with circular and rectangular apertures

The extraordinary transmission (ET) due to localized surface plasmon (LSP) and propagating surface plasmon (PSP) resonances of terahertz wave through a copper film perforated with circular and rectangular apertures is investigated theoretically and experimentally. Considering that the field distributions of LSP and PSP resonances are determined by the shape and periods of the apertures on the film, the relations between extraordinary and the geometrical parameters of the apertures are investigated. The intensities of the ETs induced by the PSP resonances mode [1, 1] are much stronger than the fundamental ones [1, 0] and [0, 1]. Our finds provide another effective method to tailor the extraordinary THz transmission in sub-wavelength metallic aperture structures.     

Spontaneous emission by an ensemble of dipoles coupled to a plasmonic nanoresonator

ABSTRACT

Spontaneous emission from ensembles of quantum emitters (QEs) such as atoms, molecules or semiconductor quantum dots can be greatly enhanced by cooperative effects arising from electromagnetic correlations. We describe a cooperative mechanism for emission of light by an ensemble of QEs based upon cooperative energy transfer from QEs to localized surface plasmons in metal-dielectric structures followed by plasmon radiation at a rate that scales with the ensemble size. For large QE ensembles saturating the plasmon mode volume, we derive universal, i.e. independent of local field distribution, expression for cooperative Purcell factor that can by far exceed the field enhancement limits for individual QE in a hot spot. We also derive radiated power spectrum that retains the plasmon resonance lineshape and, in contrast to common cooperative mechanisms, is insensitive to natural variations of QEs' emission frequencies.     

Intraparticle surface plasmon coupling in quasi-one-dimensional nanostructures

The optical properties of two-component quasi-one-dimensional nanostructures consisting of Au and Ni blocks have been investigated. The optically inactive component Ni plays a relaying role in the surface plasmon coupling both for the dipole mode and for the higher-order modes of gold blocks. The experimental results exhibit that the free electrons in Ni participate in the optical coupling phenomenon and that plasmon excitations in the Au blocks induce the free electrons in Ni to oscillate.     

Application du modèle théorique à l'étude des pertes d'énergie caractéristiques des électrons transmis et rétrodiffusés dans le cas de l'aluminium

This paper deals with a theoretical model concerning transmission and backscattering of electrons by thin self-supported aluminium targets.This model is based on the Boltzmann equation, and our studies are limited to low energy losses; we show the existence of plasmon peaks in the energy distributions of electrons.The effects of physical parameters appearing during interactions with the jellium are analysed, and the sensitivity of our model is checked.     

Plasmon‐Driven Rapid In Situ Formation of Luminescence Single Crystal Nanoparticle

Single crystal nanomaterials are very important for the fundamental investigation and application of luminescence. However, a very critical growth condition or high temperature treatment is always required for their preparation. Here, an easy and rapid in situ achievement of a single crystal luminescent material is realized by taking advantage of plasmon‐induced thermal and catalysis effects. With the assistance of localized surface plasmon resonance of Au nanoparticles, polycrystalline NaYF₄ transforms to single crystal Y₂O₃ in tens of milliseconds, resulting in remarkable improvement of luminescence emission. It is important to point out that the single crystal transformation is also achieved even at a very low temperature, which is impossible with conventional approaches. Such a convenient and efficient plasmon assisted scheme provides a new technology for the rapid achievement of single crystal materials and extends the application of surface plasmon to a much broader field.