Detuned electrical dipoles for plasmonic sensing

We demonstrate that a pair of electrical dipolar scatterers resonating at different frequencies, i.e., detuned electrical dipoles, can be advantageously employed for plasmonic sensing of the environment, both as an individual subwavelength-sized sensor and as a unit cell of a periodic array. It is shown that the usage of the ratio between the powers of light scattered into opposite directions (or into different diffraction orders), which peaks at the intermediate frequency, allows one to reach a sensitivity of ≈ 400 nm/RIU with record high levels of figure of merit exceeding 200. Qualitative considerations are supported with detailed simulations and proof-of-principle experiments using lithographically fabricated gold nanorods with resonances at 800 nm.     

Self-organized silver nanoparticles for three-dimensional plasmonic crystals

Metal nanostructures that support surface plasmons are compelling as plasmonic circuit elements and as the building blocks for metamaterials. We demonstrate here the spontaneous self-assembly of shaped silver nanoparticles into three-dimensional plasmonic crystals that display a frequency-selective response in the visible wavelengths. Extensive long-range order mediated by exceptional colloid monodispersity gives rise to optical passbands that can be tuned by particle volume fraction. These metallic supercrystals present a new paradigm for the fabrication of plasmonic materials, delivering a functional, tunable, completely bottom-up optical element that can be constructed on a massively parallel scale without lithography.     

Toward plasmonic polymers

We establish the concept of a plasmonic polymer, whose collective optical properties depend on the repeat unit. Experimental and theoretical analyses of the super- and sub- radiant plasmon response of plasmonic polymers comprising repeat units of single nanoparticles or dimers of gold nanoparticles show that (1) the redshift of the lowest energy coupled mode becomes minimal as the chain approaches the infinite chain limit at a length of ～10 particles, (2) the presence and energy of the modes are sensitive to the geometries of the constituents, that is, repeat unit, but (3) spatial disorder and nanoparticle heterogeneity have only small effects on the super-radiant mode.     

Chiral Surface Lattice Resonances

Collective excitation of periodic arrays of metallic nanoparticles by coupling localized surface plasmon resonances to grazing diffraction orders leads to surface lattice resonances with narrow line width. These resonances may find numerous applications in optical sensing and information processing. Here, a new degree of freedom of surface lattice resonances is experimentally investigated by demonstrating handedness-dependent excitation of surface lattice resonances in arrays of chiral plasmonic crescents. The self-assembly of particles used as mask and modified colloidal lithography is applied to produce arrays of planar and 3D gold crescents over large areas. The excitation of surface lattice resonances as a function of the interparticle distance and the degree of order within the arrays is investigated. The chirality of the individual 3D crescents leads to the formation of chiral lattice modes, that is, surface lattice resonances that exhibit optical activity.     

Chaotic Third Sound Resonances

There are three independent phenomena that compete to determine the line shapes of third sound resonances in a circular cavity. First, anharmonic terms in the hydrodynamic equations of motion lead to the usual hysteresis on a mugti-valued response function. Second, wave coupling to vortices pinned in the film modify the resonant frequency as changes in the persistent current are induced. Finally, nonlinear dissipation can lead to saturation. The first two of these have been observed to resugt in continuous (not just transient) temporal behavior of the resonance amplitude with a fixed drive. Both cyclical and chaotic behaviors have been observed. The effects are dependent on the ability of the driven wave to either accelerate or decelerate the persistent current onto different amplitude branches of the mugti-valued resonance.     

Agglomerating vibro-fluidization behavior of nano-particles

An experiment study of agglomerating fluidization behavior of three kinds of nano-particles (SiO₂, TiO₂, ZnO) in vibro-fluidized bed (VFB) has been performed. At certain amplitude (3 mm) of vibrations applied, the minimum fluidization velocity decreases, whilst the equilibrium pressure drop increases with increase in the vibration frequency. The minimum fluidization velocity is nearly independent of the vibration amplitude at almost constant frequency of about 40 Hz, whilst the equilibrium pressure increases. Using the linear regression, the Richardson–Zaki exponents of three kinds of nano-particles have been calculated. R–Z analyses indicate that the particulate fluidization degree of cohesive particles can be greatly improved by vibration force.     

Patterned resonance plasmonic microarrays for high-performance SPR imaging

We report a novel optical platform based on SPR generation and confinement inside a defined three-dimensional microwell geometry that leads to background resonance-free SPR images. The array shows an exceptionally high signal-to-noise ratio (S/N > 80) for imaging analysis and subnanometric thickness resolution. An angular sensitivity of 1°/0.01 RIU has been achieved and the signal to background ratio (S/B) improves to 20, 1 order of magnitude higher than that of the best literature results. The design proves effective for probing-supported lipid membrane arrays in real time with a thickness resolution of 0.24 nm and allows for imaging analysis of microfluidic circuits where resonant spots are separated by only one pixel (～7 μm). The high image quality and unique chip geometry open up new avenues for array screening and biomicrofluidics using SPRi detection.     

微反应器法纳米颗粒制备技术

微反应器法以其特殊的微反应环境而在纳米颗粒的制备中受到越来越广泛的重视，从微反应器的组成和性质入手，介绍了微反应器内纳米颗粒的形成机理及反应特点，举例说明了该法在纳米颗粒制备中的应用，对该法在纳米颗粒制备中的前景作了展望。     

Nanostructured plasmonic medium for terahertz bandwidth all-optical switching

Periodic nanostructuring can enhance the optical nonlinearity of plasmonic metals by several orders of magnitude. By patterning a gold film, the largest sub-100 femtosecond nonlinearity is achieved, which is suitable for terahertz rate all-optical data processing as well as ultrafast optical limiters and saturable absorbers.     

Self-orienting nanocubes for the assembly of plasmonic nanojunctions

Plasmonic hot spots are formed when metal surfaces with high curvature are separated by nanoscale gaps and an electromagnetic field is localized within the gaps. These hot spots are responsible for phenomena such as subwavelength focusing, surface-enhanced Raman spectroscopy and electromagnetic transparency, and depend on the geometry of the nanojunctions between the metal surfaces. Direct-write techniques such as electron-beam lithography can create complex nanostructures with impressive spatial control but struggle to fabricate gaps on the order of a few nanometres or manufacture arrays of nanojunctions in a scalable manner. Self-assembly methods, in contrast, can be carried out on a massively parallel scale using metal nanoparticle building blocks of specific shape. Here, we show that polymer-grafted metal nanocubes can be self-assembled into arrays of one-dimensional strings that have well-defined interparticle orientations and tunable electromagnetic properties. The nanocubes are assembled within a polymer thin film and we observe unique superstructures derived from edge-edge or face-face interactions between the nanocubes. The assembly process is strongly dependent on parameters such as polymer chain length, rigidity or grafting density, and can be predicted by free energy calculations.     

Isolation of discrete nanoparticle-DNA conjugates for plasmonic applications

Discrete DNA-gold nanoparticle conjugates with DNA lengths as short as 15 bases for both 5 and 20 nm gold particles have been purified by anion-exchange HPLC. Conjugates comprising short DNA (<40 bases) and large gold particles (> or =20 nm) are difficult to purify by other means and are potential substrates for plasmon coupling experiments. Conjugate purity is demonstrated by hybridizing complementary conjugates to form discrete structures, which are visualized by TEM.     

Au double nanopillars with nanogap for plasmonic sensor

We propose a simple, precise, and wafer-scale fabrication technique for Au double nanopillar (DNP) arrays with nanogaps of several tens of nanometers. An Au DNP was simply constructed by alternately laminating thin layers of Au and polymer on a template and selectively removing the thin layers. This DNP array was expected to exhibit a specific plasmonic property induced by its narrow gap. When measuring the refractive index sensitivity (RIS), Au DNP arrays with 33 nm gaps exhibited a high RIS of 1075 nm RIU(-1) and showed a higher sensor figure of merit than the alternative structures, which did not have a nanogap structure but had almost the same surface area. This indicated that the enhanced plasmon electromagnetic field induced by the nanogap structure improved sensor performance. Our fabrication technique and the optical properties of the nanogap structure will provide useful information for developing new plasmonic applications with nanogap structures.     

纳米等离子体激光器研究进展

半导体激光器在生物技术、信息存储、光子医学诊疗等方面得到了广泛应用。随着纳米技术和纳米光子学的发展,紧凑微型化激光器应用前景引人关注。当激光器谐振腔尺寸减小到发射波长时,电磁谐振腔中将产生更为有趣的物理效应。因此,在发展低维、低泵浦阈值的超快相干光源,以及纳米光电集成和等离激元光路时,减小半导体激光器的三维尺寸至关重要。在本综述中,首先介绍了纳米等离子体激光器中的谐振腔模式增益和限制因子的总体理论,并综述了金属-绝缘材料-半导体纳米(MIS)结构或其它相关金属覆盖半导体结构的纳米等离子体激光器各方面的总体研究进展。特别地,对基于MIS结构的等离子体谐振腔实现纳米等离子体激光器三维衍射极限的突破,进行了详细的介绍。本文也介绍并展望了纳米等离子体激光器的技术挑战和发展趋势,为纳米激光器进一步研究提供参考。

     

Charnia-like broadband plasmonic nano-antenna

Charnia was a pre-Cambrian life-form that exhibited a fractal structure to improve the extraction of nutrients from the pre-historic seas. Inspired by its fractal structure, this paper studies the potential application of these self-similarity fractal structures to create a plasmonic nano-antenna that can operate over a large linewidth. These devices are studied both theoretically and experimentally. It is shown that these nano-antennas can produce electric field enhancements above 8 over 200?nm range and surface enhanced Raman scattering (SERS) enhancements higher than 10⁵.     

Genetically engineered plasmonic nanoarrays

In the present Letter, we demonstrate how the design of metallic nanoparticle arrays with large electric field enhancement can be performed using the basic paradigm of engineering, namely the optimization of a well-defined objective function. Such optimization is carried out by coupling a genetic algorithm with the analytical multiparticle Mie theory. General design criteria for best enhancement of electric fields are obtained, unveiling the fundamental interplay between the near-field plasmonic and radiative photonic coupling. Our optimization approach is experimentally validated by surface-enhanced Raman scattering measurements, which demonstrate how genetically optimized arrays, fabricated using electron beam lithography, lead to order of ten improvement of Raman enhancement over nanoparticle dimer antennas, and order of one hundred improvement over optimal nanoparticle gratings. A rigorous design of nanoparticle arrays with optimal field enhancement is essential to the engineering of numerous nanoscale optical devices such as plasmon-enhanced biosensors, photodetectors, light sources and more efficient nonlinear optical elements for on chip integration.     

A plasmonic fano switch

Plasmonic clusters can support Fano resonances, where the line shape characteristics are controlled by cluster geometry. Here we show that clusters with a hemicircular central disk surrounded by a circular ring of closely spaced, coupled nanodisks yield Fano-like and non-Fano-like spectra for orthogonal incident polarization orientations. When this structure is incorporated into an uniquely broadband, liquid crystal device geometry, the entire Fano resonance spectrum can be switched on and off in a voltage-dependent manner. A reversible transition between the Fano-like and non-Fano-like spectra is induced by relatively low (～6 V) applied voltages, resulting in a complete on/off switching of the transparency window.     

Fast Computation Algorithm for Discrete Resonances among Gravity Waves

Traditionally resonant interactions among short waves with large real wave-numbers were described statistically, and only a small domain in the spectral space with integer wave-numbers, i.e. discrete resonances, had to be studied separately in resonators. Numerical simulations of the last few years have shown unambiguously the existence of some discrete effects in the short-wave part of the wave spectrum. Newly presented model of laminated turbulence explains theoretically the appearance of these effects, thus putting forth a novel problem – construction of fast algorithms for computation of solutions of resonance conditions with integer wave-numbers of orders 10³ and more. Example of such an algorithm for 4-wave interactions of gravity waves is given. Its generalization for different types of waves is briefly discussed.     

Vertical plasmonic resonant nanocavities

We demonstrate plasmonic modes in a vertical nanocavity with an air output window at the top surface and Ag reflectors. The resonances of surface plasmon polaritons are investigated using cathodoluminescence spectroscopy. The resonant modes are determined by comparing experiment and theoretical simulations. The plasmon dispersion relation in the vertical nanocavities shows a strong confinement to the electromagnetic field, and the smallest modal volume is only 0.0014 μm(3). Our work provides insights into the development of nanoscale plasmonic vertical cavity surface-emitting lasers.