Showing papers by "Xiang Zhang published in 2006"
TL;DR: A new class of ultrasonic metamaterials consisting of an array of subwavelength Helmholtz resonators with designed acoustic inductance and capacitance with an effective dynamic modulus with negative values near the resonance frequency is reported.
Abstract: The emergence of artificially designed subwavelength electromagnetic materials, denoted metamaterials, has significantly broadened the range of material responses found in nature. However, the acoustic analogue to electromagnetic metamaterials has, so far, not been investigated. We report a new class of ultrasonic metamaterials consisting of an array of subwavelength Helmholtz resonators with designed acoustic inductance and capacitance. These materials have an effective dynamic modulus with negative values near the resonance frequency. As a result, these ultrasonic metamaterials can convey acoustic waves with a group velocity antiparallel to phase velocity, as observed experimentally. On the basis of homogenized-media theory, we calculated the dispersion and transmission, which agrees well with experiments near 30 kHz. As the negative dynamic modulus leads to a richness of surface states with very large wavevectors, this new class of acoustic metamaterials may offer interesting applications, such as acoustic negative refraction and superlensing below the diffraction limit.
1,562 citations
TL;DR: Using an unbiased genome-wide RNA interference screen in Drosophila S2 cells, 75 hits are identified that strongly inhibited Ca(2+) influx upon store emptying by thapsigargin, including Stim and olf186-F, a member of a highly conserved family of four-transmembrane spanning proteins with homologs from Caenorhabditis elegans to human.
Abstract: Recent studies by our group and others demonstrated a required and conserved role of Stim in store-operated Ca(2+) influx and Ca(2+) release-activated Ca(2+) (CRAC) channel activity. By using an unbiased genome-wide RNA interference screen in Drosophila S2 cells, we now identify 75 hits that strongly inhibited Ca(2+) influx upon store emptying by thapsigargin. Among these hits are 11 predicted transmembrane proteins, including Stim, and one, olf186-F, that upon RNA interference-mediated knockdown exhibited a profound reduction of thapsigargin-evoked Ca(2+) entry and CRAC current, and upon overexpression a 3-fold augmentation of CRAC current. CRAC currents were further increased to 8-fold higher than control and developed more rapidly when olf186-F was cotransfected with Stim. olf186-F is a member of a highly conserved family of four-transmembrane spanning proteins with homologs from Caenorhabditis elegans to human. The endoplasmic reticulum (ER) Ca(2+) pump sarco-/ER calcium ATPase (SERCA) and the single transmembrane-soluble N-ethylmaleimide-sensitive (NSF) attachment receptor (SNARE) protein Syntaxin5 also were required for CRAC channel activity, consistent with a signaling pathway in which Stim senses Ca(2+) depletion within the ER, translocates to the plasma membrane, and interacts with olf186-F to trigger CRAC channel activity.
834 citations
TL;DR: In this paper, an experimental test and theoretical analysis on how and why z-fibre pins can improve the resistance to impact loading and post-impact compression was presented. But, the results were limited to three types of materials: carbon/epoxy T300/914C with nominal thicknesses of 2, 4, and 6mm.
175 citations
TL;DR: Finite-difference time-domain simulations in conjunction with a developed analytical theory show that efficient energy transfer with signal attenuation of less then 0.57 dB/microm and group velocity higher than 1/4c can be achieved.
Abstract: A one-dimensional magnetic plasmon propagating in a linear chain of single split ring resonators is proposed. The subwavelength size resonators interact mainly through exchange of conduction current, resulting in stronger coupling as compared to the corresponding magneto-inductive interaction. Finite-difference time-domain simulations in conjunction with a developed analytical theory show that efficient energy transfer with signal attenuation of less then 0.57 dB/microm and group velocity higher than 1/4c can be achieved. The proposed novel mechanism of energy transport in the nanoscale has potential applications in subwavelength transmission lines for a wide range of integrated optical devices.
161 citations
TL;DR: In this paper, the authors proposed an optical far-field superlens (FSL) for imaging beyond the diffraction limit, which is composed of a properly designed periodically corrugated metallic slab-based super-lens with a specific strong-broadband wavenumber excitation of surface-plasmon polaritons supported by the nanostructured metallic grating.
Abstract: A conventional optical superlens for imaging beyond the diffraction limit produces images only in the near-field zone of the superlens. In contrast, an optical far-field superlens (FSL) device has a remarkable transmission property that leads to a one-to-one relationship between the far-field and the near-field angular spectra. This property makes the device suitable for imaging beyond the diffraction limit from far-field measurement. This specific FSL is composed of a properly designed periodically corrugated metallic slab-based superlens. Through the numerical design and parameter study, we show that the transmission property of this FSL is based on a specific strong-broadband wavenumber excitation of surface-plasmon polaritons supported by the nanostructured metallic grating.
153 citations
TL;DR: It is found that 40% of new human exons are alternatively spliced, and most of these are cassette exons (exons that are either included or skipped in their entirety) with low inclusion rates, which suggests that de novo recruitment rather than shuffling is the major route by which exonsare added to genes.
Abstract: Orthologous gene structures in eight vertebrate species were compared on a genomic scale to detect the birth and maturation of new internal exons during the course of evolution. We found that 40% of new human exons are alternatively spliced, and most of these are cassette exons (exons that are either included or skipped in their entirety) with low inclusion rates. This proportion decreases steadily as older and older exons are examined, even as splicing efficiency increases. Remarkably, the great majority of new cassette exons are composed of highly repeated sequences, especially Alu. Many new cassette exons are 5′ untranslated exons; the proportion that code for protein increases steadily with age. New protein-coding exons evolve at a high rate, as evidenced by the initially high substitution rates (Ks and Ka), as well as the SNP density compared with older exons. This dynamic picture suggests that de novo recruitment rather than shuffling is the major route by which exons are added to genes, and that species-specific repeats could play a significant role in recent evolution.
145 citations
TL;DR: Experimental results concur well with theoretical predictions and highlight the requirement for the phase matching of SPP sources in the grating to achieve the maximum enhancement of the SPP wave at the focal point.
Abstract: We report the generation and focusing of surface plasmon polariton (SPP) waves from normally incident light on a planar circular grating milled into a silver film. The focusing mechanism is explained by using a simple coherent interference model of SPP generation on the circular grating by the incident field. Experimental results concur well with theoretical predictions and highlight the requirement for the phase matching of SPP sources in the grating to achieve the maximum enhancement of the SPP wave at the focal point. NSOM measurements show that the plasmonic lens achieves more than a 10-fold intensity enhancement over the intensity of a single ring of the in-plane field components at the focus when the grating design is tuned to the SPP wavelength. We discuss the technique’s adaptability for surface enhanced nano-scale spectroscopy.
140 citations
TL;DR: In this article, the plasmon resonance of Au∕SiO2 multilayered nanodisks has been studied using light scattering spectroscopy and numerical calculations, and it has been shown that slicing one metal layer into metal multilayers leads to higher scattering intensity and more hot spots, or regions of strong field enhancement.
Abstract: The plasmon resonance of Au∕SiO2 multilayered nanodisks was studied using light scattering spectroscopy and numerical calculations. Compared to single layered Au nanodisks, multilayered nanodisks exhibit several distinctive properties including significantly enhanced plasmon resonances and tunable resonance wavelengths which can be tailored to desired values by simply varying dielectric layer thickness while the particle diameter is kept constant. Numerical calculations show that slicing one metal layer into metal multilayers leads to higher scattering intensity and more “hot spots,” or regions of strong field enhancement. This tunable and augmented plasmon resonance holds a great potential in the applications of surface-enhanced Raman scattering (SERS).
116 citations
TL;DR: In this paper, the focus position of a plasmonic lens can be adjusted by adjusting the angle of the incident light similar to conventional lenses, which can be used in nanoscale photonics, biological sensing, and manipulation.
Abstract: We report the experimental realization of tuning the focus position of a plasmonic lens by adjusting the angle of the incident light similar to conventional lenses. A circular slit in silver film acts as both a surface plasmon polariton coupler and a plasmonic focusing lens. At small incident angles, the plasmonic lens has a very good focus with the position depending only on the angle of the incident beam. Numerical simulations of the focusing properties, including polarization dependence, agree well with experimental observations. This tunable plasmonic lens can be used in nanoscale photonics, biological sensing, and manipulation.
111 citations
TL;DR: Strong coupling effect of magnetic polariton is discovered in this system, which explains why TML structure reveals better negative-refraction property than the reported double-metal-layer (DML) structure.
Abstract: The optical propagation properties and magnetic polariton behaviors in perforated metal/dielectric layered structures are numerically investigated at near-IR region A developed three-metal-layer (TML) structure is specially inspected as a simple case Strong coupling effect of magnetic polariton is discovered in this system, which explains why TML structure reveals better negative-refraction property than the reported double-metal-layer (DML) structure A clear LC-circuit model is presented to describe the physical mechanism of this coupling effect of magnetic polaritons Detailed results show that the thickness of metal layer influences the transmission greatly and an optimum value is found
84 citations
TL;DR: By probing the modification of the critical indices for high-order moments of intensity enhancement caused by the delocalized states, this work provides the first experimental evidence for the coexistence of localized and delocalization surface plasmon modes in percolating metal films.
Abstract: Near-field intensity statistics in semicontinuous silver films over a wide range of surface coverage are investigated using near-field scanning optical microscopy. The variance of intensity fluctuations and the high-order moments of intensity enhancement exhibit local minima at the percolation threshold. This reduction in local field fluctuations results from resonant excitation of delocalized surface plasmon modes. By probing the modification of the critical indices for high-order moments of intensity enhancement caused by the delocalized states, we provide the first experimental evidence for the coexistence of localized and delocalized surface plasmon modes in percolating metal films.
TL;DR: A novel technique to precisely determine the Raman enhancement factor in single nanoplasmonic resonators (TNPRs) is developed, which eliminates the issues such as large size variations, cluster aggregation, and interparticle effects common in preparing SERS substrates using conventional chemical synthesis or batch fabrication methods.
Abstract: We have developed a novel technique to precisely determine the Raman enhancement factor in single nanoplasmonic resonators (TNPRs). TNPRs are lithographically defined metallodielectric nanoparticles composed of two silver disks stacked vertically, separated by a silica layer. At resonance, the local electromagnetic fields are enhanced at the TNPR surface, making it an ideal surface-enhanced Raman scattering (SERS) active substrate. The ability to control the dimensions of the metallic and dielectric layers offers the unique advantage of fine-tuning the plasmon resonance frequency to maximize the enhancement of the Raman signal. Furthermore, by selective shielding of the outer surface of the metallic structure, the efficiency can be further enhanced by guiding the molecular assembly to the locations that exhibit strong electromagnetic fields. We experimentally demonstrate SERS enhancement factors of (6.1 ± 0.3) × 1010, with the highest enhancement factor being achieved by using an individual nanoparticle. ...
TL;DR: In this article, a simple and efficient computational approach is presented for analyzing the benefits of through-thickness pins for restricting debond failure in joints, where tractions acting on the fracture surfaces of the debond crack are prescribed as functions of the crack displacement, which are available in simple forms that summarize the complex deformations to a reasonable accuracy.
TL;DR: In this article, a coarsening kinetics developed by Lifshitz and Slyozov [J. Phys. Chem. Solids 19, 35 (1961)] and Wagner [Z. Elektrochem. 65, 581 (19 1961)] was used to estimate the activation energy of the coarsens process.
Abstract: Postgrowth annealing was carried out on ZnO thin films grown by metal-organic chemical-vapor deposition. It was found from the scanning electron microscopy and atomic force microscopy measurements that the morphology of the thin films changed drastically after annealing. The as-grown thin films consist of fine nanoscale-sized sheets with random orientation. Upon annealing at 800°C, the ZnO nanosheets changed to three-dimensional nanoneedles. The different types of the mass transport mechanisms are discussed and correlated with the experimental results. A coarsening kinetics developed by Lifshitz and Slyozov [J. Phys. Chem. Solids 19, 35 (1961)] and Wagner [Z. Elektrochem. 65, 581 (1961)] was used to estimate the activation energy of the coarsening process. The activation energy of the Ostwald ripening in ZnO films was estimated in the first attempt, and the value is at around 1.33eV. Hall effect and photoluminescence measurements were carried out to investigate the effect of coarsening on electrical and o...
TL;DR: In this article, a theoretical model is developed to analyze the deflection and adhesion between thin polymer beams under capillary force, and a sublimation process is successfully developed to release the 3D microstructures without the adhesion.
Abstract: Micro-stereolithography (μSL) is capable of fabrication of highly complex three-dimensional (3D) microstructures by selectively photo-induced polymerization from the monomer resin. However, during the evaporative drying of structures from liquid resin, the 3D microstructures often collapse due to the capillary force. In this work, a theoretical model is developed to analyze the deflection and adhesion between thin polymer beams under capillary force. The detachment length of the test structures and adhesion energy of a typical μSL polymer (HDDA) are obtained experimentally which are important for MEMS structure design. Finally, we successfully developed a sublimation process to release the 3D microstructures without the adhesion.
TL;DR: In this paper, the authors describe a fully integrated study of the residual stress distribution accompanying state-of-the-art fusion welds in 2024-T4 aluminum alloy, and how it is affected by subsequent machining and service loading.
Abstract: Although residual stress in welded structures and components has long been known to have an effect on their fatigue performance, access to reliable, spatially accurate residual stress field data has been limited. Recent advances in neutron and synchrotron X-ray diffraction allow a far more detailed picture of weld residual stress fields to be obtained that permits the development and use of predictive models that can be used for accurate design against fatigue in aircraft structures. This paper describes a fully integrated study of the three-dimensional residual stress distribution accompanying state-of-the-art fusion welds in 2024-T4 aluminum alloy, and how it is affected by subsequent machining and service loading. A particular feature of this work has been the development of techniques allowing the nondestructive evaluation of the residual stress field in the full range of specimens used to provide the design data required for welded aircraft structures and the integration of this information into all aspects of damage tolerant design.
TL;DR: In this paper, the dispersion of the refractive index was studied by considering a single electronic oscillator model, and the band gaps of the films were estimated from Tauc's law and showed a decreasing tendency to that of the bulk SrTiO3 with the substrate temperatures increasing.
Abstract: SrTiO3 thin films were deposited on vitreous silica substrates at various substrate temperatures (300–700°C) by rf magnetron sputtering technique. The transition from amorphous phase to polycrystalline phase for the films occurred at the substrate temperatures of 300–400°C. Their optical properties were investigated by transmittance measurements. The fitting method was used to calculate the refractive index and the film thickness from the transparent region of the transmittance spectra. The refractive index increased and the film thickness decreased with the substrate temperatures increasing. The dispersion of the refractive index was studied by considering a single electronic oscillator model. The band gaps of the films were estimated from Tauc’s law and showed a decreasing tendency to that of the bulk SrTiO3 with the substrate temperatures increasing. These results provide some useful references for the potential application of SrTiO3 films in integrated optics devices.
TL;DR: By tailoring the dispersion curve of surface plasmons (SPs) of a thin metallic film surrounded by dielectric half-spaces, it was shown that the group velocity of the symmetric mode is always positive, while the group velocities of the anti-symmetric mode can be negative as discussed by the authors.
Abstract: By tailoring the dispersion curve of surface plasmons (SPs) of a thin metallic film surrounded by dielectric half-spaces, it is shown that the group velocity of the symmetric mode is always positive, while the group velocity of the anti-symmetric mode can be negative. Consequently, the forward and backward propagation of SPs, in which the energy flow is respectively parallel or antiparallel to the wave vector, can be realized. The physical origin of the intriguing backward SPs is given. Furthermore, schemes for the negative refraction and imaging of SPs are proposed by incorporating two plasmon modes with group velocities of opposite signs.
TL;DR: In this paper, the electron diffraction patterns of Nd 0.75 Na 0.25 MnO 3 were recorded at various temperatures, and it was found that the Mn 3+ and Mn 4+ ions formed zigzag chains in the a-c plane of the orthorhombic lattice (space group Pnma).
Abstract: The electron diffraction patterns of Nd 0.75 Na 0.25 MnO 3 were recorded at various temperatures. Superlattice reflection spots were observed below 170 K, which provides direct evidence of an ordered arrangement of Mn 3+ and Mn 4+ cations in this compound at low temperature. By further analyzing the diffraction patterns, the Mn 3+ and Mn 4+ ions were found to form zigzag chains in the a – c plane of the orthorhombic lattice (space group Pnma ). The magnetic, electrical-transport and thermal-transport properties of the compound were also studied. It is found that the specimen shows insulator-like characteristics in zero field, whereas a re-entrant ferromagnetic metal transition is observed when a strong magnetic field is applied. The ratio of the thermal conductivity to the electrical conductivity strongly deviates from the Wiedemann–Franz law , even in the ferromagnetic metallic state.
TL;DR: Berbamine induces caspase-3-mediated apoptosis of Ph+ leukemia cells through inhibiting phosphorylation of p210 bcr/abl protein and down-regulating its chaperone Hsp90 protein.
Abstract: OBJECTIVE To investigate the mechanism of apoptosis of chronic myeloid leukemia (CML) cells induced by the novel p210 bcr/abl inhibitor berbamine METHODS Human Ph+ CML leukemia K562 cells, which express endogenous p210 bcr/abl protein, were cultured in RPMI 1640 and treated with berbamine as indicated time and dose Flow cytometry (FCM) and Annexin-V-Fluos/PI staining kit were used to evaluate the apoptosis of leukemic cells; FCM and cytoperm/cytofix plus Caspase-3-McAb-PE were employed to measure the leukemic cells with activated Caspase-3 Phosphorylation of p210 bcr/abl protein in the leukemic cells were assessed by a combination of immunoprecipitation (IP) with c-abl antibody and Western blotting with p-Tyr (pY99) antibody The protein levels of p210 bcr/abl, Hsp90 and Hsp70 in the leukemic cells were determined by Western blotting with antibodies to c-abl, Hsp90, and Hsp70 respectively RESULTS After treatment with berbamine at 8 microg/ml for 48 h, the percentages of leukemic cells expressing activated caspase-3 and apoptotic cells were 4569% and 4843% respectively IP and WB results showed that berbamine at low concentration markedly inhibited phosphorylation of p210 bcr/abl protein in the leukemia cells, and the amount of phosphorylated p210 bcr/abl in the leukemia cells exposed to berbamine at 8 microg/ml for 6 h were only 841% of that of untreated leukemia cells without the protein levels of p210 bcr/abl down-regulated Significantly, berbamine also down-regulated chaperone Hsp90 protein, and the amount of Hsp90 protein in the leukemia cells treated with berbamine at 8 microg/ml for 48 h accounted for 1837% of that of the untreated leukemia cells Berbamine at 8 microg/ml had no obvious effect on chaperone Hsp70 protein expression associated with the resistance of leukemia cells to apoptosis CONCLUSION (1) Berbamine induces caspase-3-mediated apoptosis of Ph+ leukemia cells through inhibiting phosphorylation of p210 bcr/abl protein and down-regulating its chaperone Hsp90 protein (2) Unlike Hsp90 inhibitor GA that upregulates Hsp70, berbamine has no obvious effect on chaperone Hsp70 protein expression in leukemia cells, suggesting that berbamine may be a novel class of Hsp90 inhibitor, and further study is required
TL;DR: In this article, a planar superlens with periodical corrugation is proposed to obtain far-field images of 40 nm lines with a 30 nm gap from far field data with a properly designed FSL working at 376nm wavelength.
Abstract: Recent theoretical and experimental studies have shown that imaging with resolution well beyond the diffraction
limit can be obtained with so-called superlenses. Images formed by such superlenses are, however, in the near
field only, or a fraction of wavelength away from the lens. In this paper, we propose a far-field superlens (FSL)
device which is composed of a planar superlens with periodical corrugation. We show in theory that when an
object is placed in close proximity of such a FSL, a unique image can be formed in far-field. As an example, we
demonstrate numerically that images of 40 nm lines with a 30 nm gap can be obtained from far-field data with
properly designed FSL working at 376nm wavelength.
06 Nov 2006
TL;DR: This paper proposes a model, F-cluster, for mining subspace coherent patterns from heterogeneous gene expression data and analyzes the search space of the problem and gives a naïve solution for it.
Abstract: Microarray technology is a powerful tool for geneticists to monitor interactions among tens of thousands of genes simultaneously. There has been extensive research on coherent subspace clustering of gene expressions measured under consistent experimental settings. However, these methods assume that all experiments are run using the same batch of microarray chips with similar characteristics of noise. Algorithms developed under this assumption may not be applicable for analyzing data collected from heterogeneous settings, where the set of genes being monitored may be different and expression levels may be not directly comparable even for the same gene. In this paper, we propose a model, F-cluster, for mining subspace coherent patterns from heterogeneous gene expression data. We compare our model with previously proposed models. We analyze the search space of the problem and give a naive solution for it.
TL;DR: The analytical results show that the chaotic synchronization is stable for N-->infinity in the presence of the external driving or global coupling.
Abstract: The chaotic synchronization in n-dimensional large map networks with local coupling and their size stabilities in the node number N-->infinity are studied analytically and numerically. The analytical results show that the chaotic synchronization is stable for N-->infinity in the presence of the external driving or global coupling. The numerical calculations show that, as the driving or global interaction strength increases from zero, the network states have the whole route: spatiotemporal chaotic state --> cluster chaotic synchronous state --> complete chaotic synchronous state --> spatiotemporal pattern --> spatiotemporal chaotic state.
TL;DR: In this article, a scaling theory for the electromagnetic response of semicontinuous metal films is developed by solving the surface plasmon eigenproblem, where the short-range correlations in the governing Kirchhoff Hamiltonian result in delocalization of the surface Plasmon Eigenmodes, which modifies the critical indices for the high-order field moments.
Abstract: Theoretical and experimental studies of the electromagnetic response of semicontinuous metal films are presented. A scaling theory is developed by solving the surface plasmon eigenproblem. The short-range correlations in the governing Kirchhoff Hamiltonian result in delocalization of the surface plasmon eigenmodes. Although their relative weight in the spectrum becomes asymptotically small for large systems, the existence of these delocalized states modifies the critical indices for the high-order field moments. This modification is confirmed experimentally by the near-field measurement of high-order intensity moments for percolating silver films on glass substrates.
TL;DR: In this paper, the authors present the gauge field theoretic solution to the problem of a uniformly moving screw dislocation and show that stress divergence at the core of the dislocation is removed at all time and supersonic states are found to be admissible.
TL;DR: In this paper, a new method to in situ fabricate magnesium alloy reinforced with 8 wt % of TiB2 and TiC is described, which leads to an increase on microhardness and tensile strength of magnesium matrix composites.
Abstract: A new method to in situ fabricate magnesium alloy reinforced with 8 wt % of TiB2 and TiC is described. The XRD result revealed the formation of TiB2 and TiC in master alloy magnesium matrix composites. Uniform distribution of fine reinforcement in the matrix material obtained through microstructural characterization. Mechanical characterization revealed that the presence of TiB2 and TiC leads to an increase on microhardness and tensile strength of magnesium matrix composites. Scanning electronic micrographs taken from the tensile fracture surface of magnesium matrix composites revealed typical brittle fracture.
TL;DR: In this article, a planar superlens with periodical corrugation was proposed to obtain far-field images of 40 nm lines with a 30 nm gap from far field data with properly designed FSL working at 376nm wavelength.
Abstract: Recent theoretical and experimental studies have shown that imaging with resolution well beyond the diffraction limit can be obtained with so-called superlenses. Images formed by such superlenses are, however, in the near field only, or a fraction of wavelength away from the lens. In this paper, we propose a far-field superlens (FSL) device which is composed of a planar superlens with periodical corrugation. We show in theory that when an object is placed in close proximity of such a FSL, a unique image can be formed in far-field. As an example, we demonstrate numerically that images of 40 nm lines with a 30 nm gap can be obtained from far-field data with properly designed FSL working at 376nm wavelength.
07 May 2006
TL;DR: Development of this 3D microfabricated bioreactors are expected to have direct impact on applications such as analyte controlled and modulated drug and protein delivery, drug targeting, tissue engineering, and micro- or nano-devices.
Abstract: We present here an innovative three dimensional microfabrication technology coupled with mass transport simulation to enable the design and fabrication of advanced microbioreactors. The core of our microfabrication technology is a high-resolution projection micro stereo lithography (PµSL) using a spatial light modulator as the dynamic mask. This unique technology provides a parallel fabrication of highly complex 3D microstructures. In this work, a set of poly(ethylene glycol) bioreactors are demonstrated with PµSL technology. Supported by the results of our numerical study, the precisely controlled channel density (>150/mm 2 ) in the polymer matrix and improved transport of nutrient and oxygen through advection and diffusion represent the key advantages of the microfabricated bioreactors to the traditional foam and hollow fiber based bioreactors. Development of this 3D microfabricated bioreactors are expected to have direct impact on applications such as analyte controlled and modulated drug and protein delivery, drug targeting, tissue engineering, and micro- or nano-devices.
TL;DR: In this article, the dispersion curve of surface plasmon polaritons (SPs) is shown to be of negative slope at large wave vectors, so two different anti-symmetric modes can be excited at the same frequency.
Abstract: Surface plasmon polaritons, sometimes referred to as Surface Plasmons (SPs) have brought us great opportunities to
work in nanoscale at optical frequencies. The SPs at the two surfaces of a thin metal film interact with each other, hence
generate new modes which are either symmetric or anti-symmetric. For anti-symmetric modes, the dispersion curve turns
to be of negative slope at large wave vectors, so two different anti-symmetric modes can be excited at the same
frequency. These two modes can form beats with novel features. The envelope (profile) of the beating SP waves could be
stationary, which means its shape will not change in time. Our simulation results clearly showed such phenomena, which
is a strong evidence of the SPs dispersion relations at the thin metal film. It is a proof of the existence of negative group
velocity of SPs. Beats can help us determine the difference in k and the amplitudes ratio of the two beating waves. We
also studied beating between anti-symmetric mode and symmetric mode SPs with the same frequency. The study of the
energy density distribution showed that the output from such system can be well controlled through beats formation.
Example by using NSOM (Near-field Scanning Optical Microscopy) has been simulated. The beating phenomena have a
potential application in the integrated optical circuits.
TL;DR: The plasmonic nearfield scanning optical microscopy (NSOM) as discussed by the authors can focus light into a 100 nm spot, which is at least 10 times stronger than can be obtained from conventional NSOM probes under the same illumination condition.
Abstract: Nearfield scanning optical microscopy (NSOM) offers a practical means of optical imaging at a resolution well beyond
the diffraction limit of the light. However, its applications are limited due to the strong attenuation of the light
transmitted through the sub-wavelength aperture. To solve this problem we report the development of plasmonic
nearfield scanning optical microscope with a high optical coupling efficiency. By exciting surface plasmons, plasmonic
NSOM probes are capable of focusing light into a 100 nm spot. Both numerical simulation and nearfield exposure
experiments have demonstrated that the intensity at the focal point is at least 10 times stronger than can obtained from
the conventional NSOM probes under the same illumination condition. By providing a strong nano-scale light source,
plasmonic NSOM can be used as a high speed nano-scale imaging tool for cellular visualization, molecule detection, and
many other applications requiring high temporal resolution.