A nonvolatile plasmonic switch employing photochromic molecules

We demonstrate a surface plasmon-polariton (SPP) waveguide all-optical switch that combines the unique physical properties of small molecules and metallic (plasmonic) nanostructures. The switch consists of a pair of gratings defined in an aluminum film coated with a 65 nm thick layer of photochromic (PC) molecules. The first grating couples a signal beam consisting of free space photons to SPPs that interact effectively with the PC molecules. These molecules can reversibly be switched between transparent and absorbing states using a free space optical pump. In the transparent (signal "on") state, the SPPs freely propagate through the molecular layer, and in the absorbing (signal "off") state, the SPPs are strongly attenuated. The second grating serves to decouple the SPPs back into a free space optical beam, enabling measurement of the modulated signal with a far-field detector. In a preliminary study, the switching behavior of the PC molecules themselves was confirmed and quantified by surface plasmon resonance spectroscopy. The excellent (16%) overlap of the SPP mode profile with the thin layer of switching molecules enabled efficient switching with power densities of approximately 6.0 mW/cm2 in 1.5 microm x 8 microm devices, resulting in plasmonic switching powers of 0.72 nW per device. Calculations further showed that modulation depths in access of 20 dB can easily be attained in optimized designs. The quantitative experimental and theoretical analysis of the nonvolatile switching behavior in this letter guides the design of future nanoscale optically or electrically pumped optical switches.     

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.     

A conformation- and ion-sensitive plasmonic biosensor

The versatile optical and biological properties of a localized surface plasmon resonance (LSPR) sensor that responds to protein conformational changes are illustrated. The sensor detects conformational changes in a surface-bound construct of the calcium-sensitive protein calmodulin. Increases in calcium concentration induce a 0.96 nm red shift in the spectral position of the LSPR extinction maximum (λ(max)). Addition of a calcium chelating agent forces the protein to return to its original conformation and is detected as a reversal of the λ(max) shift. As opposed to previous work, this work demonstrates that these conformational changes produce a detectable shift in λ(max) even in the absence of a protein label, with a signal:noise ratio near 500. In addition, the protein conformational changes reversibly switch both the wavelength and intensity of the resonance peak, representing an example of a bimodal plasmonic component that simultaneously relays two distinct forms of optical information. This highly versatile plasmonic device acts as a biological sensor, enabling the detection of calcium ions with a biologically relevant limit of detection of 23 μM, as well as the detection of calmodulin-specific protein ligands.     

A DNA origami plasmonic sensor with environment-independent read-out

Nano Research - DNA origami is a promising technology for its reproducibility, flexibility, scalability and biocompatibility. Among the several potential applications, DNA origami has been proposed...     

A cryogenic microwave switch

A cryogenic microwave switch has been developed which has an isolation greater than 70 db, a throughput of 0.99, and a rise time of a few nanoseconds. The switch consists of an H-plane T in which one arm contains a short and a sapphire tube containing He. The short is fixed so as to isolate the other two arms when the He is not excited. The high degree of isolation is a direct consequence of the superconducting properties of the waveguide. The tube of He is located a quarter guide wavelength from the T so that when a plasma discharge is created in it, the other two arms become tightly coupled. Plasma rise times of order several nanoseconds have been achieved by applying a high voltage dc pulse across the tube. The switch has been used to release microwave energy stored in a superconducting resonator, creating high power microwave pulses. Here we will discuss the design parameters of the switch and its observed performance.     

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.     

A simple perturbative tool to calculate plasmonic photonic bandstructures

We use first order perturbation theory to study the effect of surface plasmon polaritons on the photonic band structure of plasmonic photonic crystals. Our results are based on a simple numerical tool that we have developed to extend the standard frequency domain methods to compute the photonic band structure of plasmonic photonic crystals. For a two-dimensional honeycomb photonic crystal with a lattice constant of 500 nm placed on an aluminium substrate, we show that the band gap for TM modes is enhanced by 13%. Thus a slight variation in the effective dielectric function results in a plasmonic band structure that is not scale-invariant, which is reminiscent of the inherent non-linear properties of the effective dielectric constant.     

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.     

Biosensing with plasmonic nanosensors

Recent developments have greatly improved the sensitivity of optical sensors based on metal nanoparticle arrays and single nanoparticles. We introduce the localized surface plasmon resonance (LSPR) sensor and describe how its exquisite sensitivity to size, shape and environment can be harnessed to detect molecular binding events and changes in molecular conformation. We then describe recent progress in three areas representing the most significant challenges: pushing sensitivity towards the single-molecule detection limit, combining LSPR with complementary molecular identification techniques such as surface-enhanced Raman spectroscopy, and practical development of sensors and instrumentation for routine use and high-throughput detection. This review highlights several exceptionally promising research directions and discusses how diverse applications of plasmonic nanoparticles can be integrated in the near future.     

Three-dimensional chiral plasmonic oligomers

The living world is chiral. Chirality or the handedness of a structure or molecule is at the heart of life itself. Recently, it has been shown that plasmonic structures exhibit unprecedented and gigantic chiral optical responses. Here we show that truly three-dimensional arrangements of plasmonic "meta-atoms" only exhibit a chiral optical response if similar plasmonic "atoms" are arranged in a handed fashion as we require resonant plasmonic coupling. Moreover, we demonstrate that such particle groupings, similarly to molecular systems, possess the capability to encode their three-dimensional arrangement in unique and well-modulated spectra making them ideal candidates for a three-dimensional chiral plasmon ruler. Our results are crucial for the future design and improvement of plasmonic chiral optical systems, for example, for ultrasensitive enantiomer sensing on the single molecule level.     

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.     

Ultra-subwavelength two-dimensional plasmonic circuits

We report electronics regime (GHz) two-dimensional (2D) plasmonic circuits, which locally and nonresonantly interface with electronics, and thus offer to electronics the benefits of their ultrasubwavelength confinement, with up to 440,000-fold mode-area reduction. By shaping the geometry of 2D plasmonic media 80 nm beneath an unpatterned metallic gate, plasmons are routed freely into various types of reflections and interferences, leading to a range of plasmonic circuits, e.g., plasmonic crystals and plasmonic-electromagnetic interferometers, offering new avenues for electronics.     

A nanofluidic railroad switch for DNA

We present a metamaterial consisting of a two-dimensional, asymmetric lattice of crossed nanochannels in fused silica, with channel diameters of 80 nm to 140 nm. When DNA is introduced, it is stretched and linearized. We show that the asymmetry in channel dimensions gives rise to a preferred direction for DNA orientation and a preferred direction for transport under dc electrophoresis. Interestingly, the preferred axis of orientation and transport can be switched by 90 degrees through application of an ac voltage. We explain the results in terms of an energy landscape for polyelectrolytes that consists of entropic and dielectrophoretic contributions and whose strength and sign can be tuned by changing the ac field strength.     

Nonlinear infrared plasmonic waveguide arrays

The large negative permittivity of noble metals in the infrared region prevents the possibility of highly confined plasmons in simple waveguide structures such as thin films or rods. This is a critical obstacle to applications of nonlinear plasmonics in the telecommunication wavelength region. We theoretically propose and numerically demonstrate that such limitation can be overcome by exploiting inter-element coupling effects in a plasmonic waveguide array. The supermodes of a plasmonic array span a large range of effective indices, making these structures ideal for broadband mode-multiplexed interconnects for integrated photonic devices. We show such plasmonic waveguide arrays can significantly enhance nonlinear optical interactions when operating in a high-index, tightly bound supermode. For example, a third-order nonlinear coefficient in such a waveguide can be more than three orders of magnitude larger compared to silicon waveguides of similar dimensions. These findings open new design possibilities towards the application of plasmonics in integrated optical devices in the telecommunications spectral region.

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Enhanced dual plasmonic photocatalysis through plasmonic coupling in eccentric noble metal-nonstoichiometric copper chakogenide hetero-nanostructures

The extension of plasmonics to materials beyond the conventional noble metals opens up a novel and exciting regime after the inspiring discovery of characteristic localized surface plasmon resonances(LSPRs)in doped semiconductor nanocrystals originating from the collective oscillations of free holes in the valence band.We herein prepare colloidal monodisperse eccentric dual plasmonic noble metal-nonstoichiometric copper chalcogenide(Au@Cu_2-xSe)hybrid hetero-nanostructures with precisely controlled semiconductor shell size and two tunable LSPRs in both visible(VIS)and near-infrared(NIR)regions associated with Au and Cu_2-xSe,respectively.Through systematic evaluations of the photocatalytic performance of Au@Cu_2-xSe upon sole NIR and dual VIS+NIR simultaneous excitations,we are capable of unambiguously elucidating the role of plasmonic coupling between two dissimilar building blocks on the accelerated photocatalytic reactions with greater rate constants from both experimental and computational perspectives.The significantly enhanced strength of the electromagnetic field arising from efficient plasmonic coupling under the excitation of two LSPRs results in the superior activities of dual plasmonic Au@Cu_2-xSe in photocatalysis.The new physical and chemical insights gained from this work provide the keystone for the rational design and construction of high-quality dual-or even multi-plasmonic nano-systems with optimized properties for widespread applications ranging from photocatalysis to molecular spectroscopies.     

A new inverse-pinch plasma opening switch

An inverse-pinch plasma opening switch (POS) of a new type has been studied, which is capable of switching a 300–400 kA current at a rise time of ∼1 μs and a current fall rate of 8 × 10¹² A/s. The POS can operate at both negative and positive polarity of the central electrode.