Probing the electromagnetic field distribution within a metallic nanodisk

A Co nanolayer is used as a local probe to evaluate the vertical inhomogeneous distribution of the electromagnetic (EM) field within a resonant metallic nanodisk. Taking advantage of the direct relation between the magneto-optical activity and the electromagnetic field intensity in the Co layer, it is shown that the nonuniform EM distribution within the nanodisk under plasmon resonant conditions has maximum values close to the upper and lower flat faces, and a minimum value in the middle.     

Excitonic fano resonance in free-standing graphene

We investigate the role of electron-hole correlations in the absorption of free-standing monolayer and bilayer graphene using optical transmission spectroscopy from 1.5 to 5.5 eV. Line shape analysis demonstrates that the ultraviolet region is dominated by an asymmetric Fano resonance. We attribute this to an excitonic resonance that forms near the van Hove singularity at the saddle point of the band structure and couples to the Dirac continuum. The Fano model quantitatively describes the experimental data all the way down to the infrared. In contrast, the common noninteracting particle picture cannot describe our data. These results suggest a profound connection between the absorption properties and the topology of the graphene band structure.     

Shifts in plasmon resonance due to charging of a nanodisk array in argon plasma

A method for generating charge-induced plasmonic shifts, using argon plasma to charge nanoparticle arrays, is presented. Particles develop a negative charge, due to enhanced collisions with high-temperature electrons, in low-temperature plasmas. The negative charge generated causes a blue shift in the localized surface plasmon resonance. The dynamics of the shift were recorded and discussed. This effect could be used as a real-time method for studying the dynamics for charging in plasma.     

Ar-O2气体去除硅铁合金中金属杂质研究

硅铁合金在炼钢过程中被广泛用作合金剂和脱氧剂,其中含有的金属杂质Al,Ca,Ti会直接影响钢液的洁净度,因此采用顶吹Ar-O2气体的方法去除硅铁合金中的金属杂质。借助自动扫描电镜统计精炼前后硅铁合金中杂质相的形貌、成分、面积分数,通过ICP-AES测试金属杂质的含量变化。结果表明:硅铁合金原料中含有大量的金属杂质相,Al,Ca,Ti杂质含量分别为1.11%(质量分数,下同),0.31%,0.11%;吹气精炼5min时,Al和Ca的含量分别急剧降低至0.66%和0.13%;吹气精炼45min后,杂质元素去除速率变缓,精炼反应趋于平衡;吹气精炼120min时,Al,Ca,Ti含量分别降低至0.42%,0.014%,0.094%,去除率分别为62.16%,95.48%,14.54%。吹气精炼方法能有效去除硅铁合金中Al和Ca杂质,Ti杂质去除效果不明显。     

Local plasmon resonance at metal wedge

A local plasmon resonance on a metal wedge is studied by using the Meixner approach [J. Meixner, IEEE Trans. Antennas Propag.AP-20, 442 (1972)]. It is found that the singular field behavior of a local plasmon resonance as a function of the distance from the edge of the wedge is sensitive to the wavelength and wedge angle, and ranges from a dramatic increase in amplitude close to its theoretical limit to pure oscillatory behavior with only minor amplitude variation. Field singularities for gold, silver, and aluminum wedges are calculated. It is shown that, unlike an ideal-conductor wedge, the real part of the power index of the electric field singularity does not decrease monotonically as a function of the wedge angle, but has a minimum for some angle depending on the wavelength and material parameters. If the dielectric surrounding the wedge has a positive permittivity equal to the absolute value of that of the metal, and hence satisfies the plasmon resonance condition, then the electric field has a peculiar behavior for a wedge whose shape is close to the flat surface.     

The role of the fano resonance in multiple exciton generation in quantum dots

Technical Physics Letters - The phenomenon of interference between two pathways of electron transfer from the valence to the conduction band at a quantum dot is considered. The first way is the...     

Ring-type plasmon resonance in metallic nanoshells

A simple, approximate theoretical model of surface plasmon resonance in two-dimensional metal nanoshells is developed. The model is based on the concept of short-range surface plasmons propagating around closed circular metal nanotubes. In this model, the plasmon resonance in a metal nanotube is treated as a propagating, self-interfering plasmonic wave, in a ring-type resonance, at plasmonic wavelengths matching an integer fraction of the nanotube's effective circumference. The model is validated by detailed computer simulations based on the finite-difference time-domain method and is shown to be in full agreement with the widely used plasmon hybridization model, which is based on the quasi-static approximation.     

Tunable magnetic resonance in double layered metallic structures

Double layered metallic gratings have been investigated both theoretically and experimentally. The authors have reported that tunable magnetic resonance (MR) can be achieved by modulating the vertical chirped width dh which could be controlled conveniently in the common electron and/or ion beam microfabrications. The linear relationship between MR wavelength and dh has been reported. By introducing the difference of electric and magnetic penetration depth, an analytic formula deduced from a modified LC model has shown good agreement with the simulation results, and an effective width for trapezoidal sandwiched microstructures has been presented. Our results may provide an alternative choice for tunable MR and broad bandwidth of magnetic metamaterials.     

Ferromagnetic resonance characterization of magnetostrictive metallic glass coatings

Amorphous ferromagnetic alloys are a promising class of materials that have been successfully used as magnetostrictive elements in fiber optic magnetic sensors. We have used ferromagnetic resonance (FMR) at about 9.5 GHz to characterize highly magnetostrictive film coatings of the amorphous ferromagnetic alloy Fe₈₁B_13.5Si_3.5C_2.R.f. sputtering was used to prepare films 0.1–0.6 μm thick on glass substrates and cladded single-mode optical fibers of diameter approximately 80 μm. Because of its inherent sensitivity, the FMR technique is shown to be an excellent non-destructive probe for investigating microscopic as well as macroscopic structural inhomogeneities that may arise from the fabrication process itself, subsequent handling or thermal aging of the coatings. An added advantage of the FMR technique is that it also allows a simultaneous measurement of such material parameters as the saturation magnetostriction coefficient, the saturation magnetization, the g factor and the uniaxial magnetic anisotropy energy. The effect of thermal annealing on some of these properties is also reported.     

Accurate frequency-tuning mechanism from a wedge prism in a single-mode tunable laser

We present a new, accurate frequency-tuning mechanism in a grazing-incidence cavity for singlelongitudinal-mode oscillation in a tunable laser. A wedge prism with a small apex angle is inserted between the tuning mirror and the grating for accurate frequency tuning. In this configuration, the laser frequency can be tuned precisely by rotation of the wedge instead of the tuning mirror. This fine-tuning mechanism offers the ability to tune the frequency over more than 400 GHz without mode hop and with a tuning accuracy that is 2 orders of magnitude larger than that of conventional tuning methods.     

Removing endocrine-disrupting compounds from wastewater

This brief article highlights research work that is being carried out at the Institut für Verfahrenstechnik, RWTH-Aachen, Aachen, Germany, which is seeking to develop ways of removing endocrine-disrupting compounds from wastewater using membrane processes.     

Spectral tuning of localised surface plasmon-polariton resonance in metallic nano-crescents

The utilisation of plasmonic effects in metallic nanostructures is gaining importance for applications in molecular sensing. Of special interest is the local field enhancement effect, which enables surface-enhanced Raman scattering and significantly boosts the sensitivity of the Raman technique. For in vivo biological research, the ability to excite the resonance of localised surface plasmon-polaritons within the biological window is often desired. A new nanostructure called the nano-crescent is introduced and exhibits strong plasmonic activities within the biological window using a novel intra-particle plasmonic coupling scheme.     

Numerical evaluation of cohesive fracture parameters from a wedge splitting test

Direct determination of the parameters describing the popular cohesive crack model from experimental results, such as would be obtained from standard three-point bending or wedge splitting tests, poses a challenging problem. This paper describes a numerical method for obtaining key fracture parameters describing the softening behavior of quasibrittle materials in mode I failure. The identification problem is formulated as a special type of constrained optimization problem known in the mathematical programming literature as a mathematical program with equilibrium constraints. Experimental results of a wedge splitting test recently conducted at the Laboratory of Construction Materials, Swiss Federal Institute of Technology (LMC/EPFL) are used to illustrate applicability of the proposed method.     

Evaluation of the limits of resonance tunability in metallic nanoshells with a spectral averaging method

Spectral selectivity based on tuning the surface plasmon resonance in metallic nanoshells by variation of the relative shell thickness is shown to be limited by the interplay between scattering and absorption. To achieve resonance energies in the near infrared and infrared, relatively large cores are needed, which lead to strong and broad scattering bands and multipolar contributions in the visible. The scattering contribution to extinction is described with a new parameter Sdelta, which is defined for a wavelength range of interest A. This parameter can help in designing materials for specific applications where scattering is either hindering, as in near-infrared absorbers for visually clear windows, or actually desired, such as in particle-array-based sensors.