Electrical tuning of phase-change antennas and metasurfaces.

The success of semiconductor electronics is built on the creation of compact, low-power switching elements that offer routing, logic and memory functions. The availability of nanoscale optical switches could have a similarly transformative impact on the development of dynamic and programmable metasurfaces, optical neural networks and quantum information processing. Phase-change materials are uniquely suited to enable their creation as they offer high-speed electrical switching between amorphous and crystalline states with notably different optical properties. Their high refractive index has already been harnessed to fashion them into compact optical antennas. Here, we take the next important step, by showing electrically-switchable phase-change antennas and metasurfaces that offer strong, reversible, non-volatile, multi-phase switching and spectral tuning of light scattering in the visible and near-infrared spectral ranges. Their successful implementation relies on a careful joint thermal and optical optimization of the antenna elements that comprise a silver strip that simultaneously serves as a plasmonic resonator and a miniature heating stage. Our metasurface affords electrical modulation of the reflectance by more than fourfold at 755 nm.

Thermoplasmonic Ignition of Metal Nanoparticles.

Explosives, propellants, and pyrotechnics are energetic materials that can store and quickly release tremendous amounts of chemical energy. Aluminum (Al) is a particularly important fuel in many applications because of its high energy density, which can be released in a highly exothermic oxidation process. The diffusive oxidation mechanism (DOM) and melt-dispersion mechanism (MDM) explain the ways powders of Al nanoparticles (NPs) can burn, but little is known about the possible use of plasmonic resonances in NPs to manipulate photoignition. This is complicated by the inhomogeneous nature of powders and very fast heating and burning rates. Here, we generate Al NPs with well-defined sizes, shapes, and spacings by electron beam lithography and demonstrate that their plasmonic resonances can be exploited to heat and ignite them with a laser. By combining simulations with thermal-emission, electron-, and optical-microscopy studies, we reveal how an improved control over NP ignition can be attained.

Probing the electrical switching of a memristive optical antenna by STEM EELS.

The scaling of active photonic devices to deep-submicron length scales has been hampered by the fundamental diffraction limit and the absence of materials with sufficiently strong electro-optic effects. Plasmonics is providing new opportunities to circumvent this challenge. Here we provide evidence for a solid-state electro-optical switching mechanism that can operate in the visible spectral range with an active volume of less than (5 nm)(3) or ∼10(-6) λ(3), comparable to the size of the smallest electronic components. The switching mechanism relies on electrochemically displacing metal atoms inside the nanometre-scale gap to electrically connect two crossed metallic wires forming a cross-point junction. These junctions afford extreme light concentration and display singular optical behaviour upon formation of a conductive channel. The active tuning of plasmonic antennas attached to such junctions is analysed using a combination of electrical and optical measurements as well as electron energy loss spectroscopy in a scanning transmission electron microscope.

Nanoscale Spatial Coherent Control over the Modal Excitation of a Coupled Plasmonic Resonator System.

We demonstrate coherent control over the optical response of a coupled plasmonic resonator by high-energy electron beam excitation. We spatially control the position of an electron beam on a gold dolmen and record the cathodoluminescence and electron energy loss spectra. By selective coherent excitation of the dolmen elements in the near field, we are able to manipulate modal amplitudes of bonding and antibonding eigenmodes. We employ a combination of CL and EELS to gain detailed insight in the power dissipation of these modes at the nanoscale as CL selectively probes the radiative response and EELS probes the combined effect of Ohmic dissipation and radiation.

Backward phase-matching for nonlinear optical generation in negative-index materials.

Metamaterials have enabled the realization of unconventional electromagnetic properties not found in nature, which provokes us to rethink the established rules of optics in both the linear and nonlinear regimes. One of the most intriguing phenomena in nonlinear metamaterials is 'backward phase-matching', which describes counter-propagating fundamental and harmonic waves in a negative-index medium. Predicted nearly a decade ago, this process is still awaiting a definitive experimental confirmation at optical frequencies. Here, we report optical measurements showing backward phase-matching by exploiting two distinct modes in a nonlinear plasmonic waveguide, where the real parts of the mode refractive indices are 3.4 and -3.4 for the fundamental and the harmonic waves respectively. The observed peak conversion efficiency at the excitation wavelength of ∼780 nm indicates the fulfilment of the phase-matching condition of k(2ω) = 2k(ω) and n(2ω) = -n(ω), where the coherent harmonic wave emerges along a direction opposite to that of the incoming fundamental light.

Probing complex reflection coefficients in one-dimensional surface plasmon polariton waveguides and cavities using STEM EELS.

The resonant properties of a plasmonic cavity are determined by the size of the cavity, the surface plasmon polariton (SPP) dispersion relationship, and the complex reflection coefficients of the cavity boundaries. In small wavelength-scale cavities, the phase propagation due to reflections from the cavity walls is of a similar magnitude to propagation due to traversing the cavity. Until now, this reflection phase has been inferred from measurements of the resonant frequencies of a cavity of known dispersion and length. In this work, we present a method for measuring the complex reflection coefficients of a truncation in a 1D surface plasmon waveguide using electron energy loss spectroscopy in the scanning transmission electron microscope (STEM EELS) and show that this insight can be used to engineer custom cavities with engineered reflecting boundaries, whose resonant wavelengths and internal mode density profiles can be analytically predicted given knowledge of the cavity dimensions and complex reflection coefficients of the boundaries.

Investigation of galectin-3 function in the reproductive tract by identification of binding ligands in human seminal plasma.

PROBLEM: Galectin-3 is a ß-galactoside binding protein with immunomodulatory properties and exerts its extracellular functions via interactions with glycoconjugate ligands. Therefore, to elucidate the function of galectin-3, binding ligands in human seminal plasma were investigated. METHOD OF STUDY: Galectin-3 binding proteins were isolated from seminal plasma by affinity chromatography, and candidate ligands were identified by MS/MS. Biochemical methods were used to characterize the ability of galectin-3 to bind its ligands. RESULTS: Identified galectin-3 ligands included CD13, MUC6, PAP, PSA, and ZAG. 1D and 2D electrophoretic analysis of seminal plasma demonstrated that CD13, PAP, PSA, and ZAG immunoreactivity co-migrated with galectin-3-reactive protein bands and spots at expected molecular weights and pIs. Inhibition assays indicated that CD13, PSA, PAP, and ZAG interact with galectin-3 in a protein-carbohydrate manner. CONCLUSION: The galectin-3 binding ligands identified in this study indicate multiple roles for galectin-3 in the reproductive and immunological functions of seminal plasma.

Hot-electron photodetection with a plasmonic nanostripe antenna.

Planar metal-oxide-metal structures can serve as photodetectors that do not rely on the usual electron-hole pair generation in a semiconductor. Instead, absorbed light in one of the metals can produce a current of hot electrons when the incident photon energy exceeds the oxide barrier energy. Despite the desirable traits of convenient fabrication and room-temperature operation at zero bias of this type of device, the low power conversion efficiency has limited its use. Here, we demonstrate the benefits of reshaping one of the metallic contacts into a plasmonic stripe antenna. We use measurements of the voltage-dependence, spectral-dependence, stripe-width dependence, and polarization-dependence of the photocurrent to show that surface plasmon excitations can result in a favorable redistribution in the electric fields in the stripe that enhances the photocurrent. We also provide a theoretical model that quantifies the spectral photocurrent in terms of the electrical and optical properties of the junction. This model provides an accurate estimate of the bias dependence of the external quantum efficiency of different devices and shows that both the spatial and vectorial properties of the electric field distribution are important to its operation.

CuInSe2 nanowires from facile chemical transformation of In2Se3 and their integration in single-nanowire devices.

Nanowire solar cells are receiving a significant amount of attention for their potential to improve light absorption and charge collection in photovoltaics. Single-nanowire solar cells offer the ability to investigate performance limits for macroscale devices, as well as the opportunity for in-depth structural characterization and property measurement in small working devices. Copper indium selenide (CIS) is a material uniquely suited to these investigations. Not only could nanowire solar cells of CIS perhaps allow efficient macroscale photovoltaics to be fabricated while reducing the amount of CIS required, important for a system with possible resource limitations, but it is also a photovoltaic material for which fundamental understanding has been elusive. We here present a recipe for a scaled up vapor liquid solid based synthesis of CIS nanowires, in-depth material and property correlation of single crystalline CIS nanowires, and the first report of a single CIS nanowire solar cell. The synthesis was accomplished by annealing copper-coated In2Se3 nanowires at a moderate temperature of 350 °C, leading to solid-state reaction forming CIS nanowires. These nanowires are p-type with a resitivity of 6.5 Ωcm. Evidence is observed for a strong diameter dependence on the nanowire transport properties. The single-nanowire solar cells have an open-circuit voltage of 500 mV and a short-circuit current of 2 pA under AM 1.5 illumination.

The planar parabolic optical antenna.

One of the simplest and most common structures used for directing light in macroscale applications is the parabolic reflector. Parabolic reflectors are ubiquitous in many technologies, from satellite dishes to hand-held flashlights. Today, there is a growing interest in the use of ultracompact metallic structures for manipulating light on the wavelength scale. Significant progress has been made in scaling radiowave antennas to the nanoscale for operation in the visible range, but similar scaling of parabolic reflectors employing ray-optics concepts has not yet been accomplished because of the difficulty in fabricating nanoscale three-dimensional surfaces. Here, we demonstrate that plasmon physics can be employed to realize a resonant elliptical cavity functioning as an essentially planar nanometallic structure that serves as a broadband unidirectional parabolic antenna at optical frequencies.

Template engineering through epitope recognition: a modular, biomimetic strategy for inorganic nanomaterial synthesis.

Natural systems often utilize a single protein to perform multiple functions. Control over functional specificity is achieved through interactions with other proteins at well-defined epitope binding sites to form a variety of functional coassemblies. Inspired by the biological use of epitope recognition to perform diverse yet specific functions, we present a Template Engineering Through Epitope Recognition (TEThER) strategy that takes advantage of noncovalent, molecular recognition to achieve functional versatility from a single protein template. Engineered TEThER peptides span the biologic-inorganic interface and serve as molecular bridges between epitope binding sites on protein templates and selected inorganic materials in a localized, specific, and versatile manner. TEThER peptides are bifunctional sequences designed to noncovalently bind to the protein scaffold and to serve as nucleation sites for inorganic materials. Specifically, we functionalized identical clathrin protein cages through coassembly with designer TEThER peptides to achieve three diverse functions: the bioenabled synthesis of anatase titanium dioxide, cobalt oxide, and gold nanoparticles in aqueous solvents at room temperature and ambient pressure. Compared with previous demonstrations of site-specific inorganic biotemplating, the TEThER strategy relies solely on defined, noncovalent interactions without requiring any genetic or chemical modifications to the biomacromolecular template. Therefore, this general strategy represents a mix-and-match, biomimetic approach that can be broadly applied to other protein templates to achieve versatile and site-specific heteroassemblies of nanoscale biologic-inorganic complexes.

High speed water sterilization using one-dimensional nanostructures.

The removal of bacteria and other organisms from water is an extremely important process, not only for drinking and sanitation but also industrially as biofouling is a commonplace and serious problem. We here present a textile based multiscale device for the high speed electrical sterilization of water using silver nanowires, carbon nanotubes, and cotton. This approach, which combines several materials spanning three very different length scales with simple dying based fabrication, makes a gravity fed device operating at 100000 L/(h m(2)) which can inactivate >98% of bacteria with only several seconds of total incubation time. This excellent performance is enabled by the use of an electrical mechanism rather than size exclusion, while the very high surface area of the device coupled with large electric field concentrations near the silver nanowire tips allows for effective bacterial inactivation.

Anisotropy of chemical transformation from In2Se3 to CuInSe2 nanowires through solid state reaction.

In(2)Se(3) nanowires synthesized by the VLS technique are transformed by solid-state reaction with copper into high-quality single-crystalline CuInSe(2) nanowires. The process is studied by in situ transmission electron microscopy. The transformation temperature exhibits a surprising anisotropy, with In(2)Se(3) nanowires grown along their [0001] direction transforming at a surprisingly low temperature of 225 degrees C, while nanowires in a [11(2)0] orientation require a much higher temperature of 585 degrees C. These results offer a route to the synthesis of CuInSe(2) nanowires at a relatively low temperature as well as insight into the details of a transformation commonly used in the fabrication of thin-film solar cells.

Nanoscale Electronic Inhomogeneity in In2Se3 Nanoribbons Revealed by Microwave Impedance Microscopy.

Driven by interactions due to the charge, spin, orbital, and lattice degrees of freedom, nanoscale inhomogeneity has emerged as a new theme for materials with novel properties near multiphase boundaries. As vividly demonstrated in complex metal oxides (see refs 1-5) and chalcogenides (see refs 6 and 7), these microscopic phases are of great scientific and technological importance for research in high-temperature superconductors (see refs 1 and 2), colossal magnetoresistance effect (see ref 4), phase-change memories (see refs 5 and 6), and domain switching operations (see refs 7-9). Direct imaging on dielectric properties of these local phases, however, presents a big challenge for existing scanning probe techniques. Here, we report the observation of electronic inhomogeneity in indium selenide (In(2)Se(3)) nanoribbons (see ref 10) by near-field scanning microwave impedance microscopy (see refs 11-13). Multiple phases with local resistivity spanning 6 orders of magnitude are identified as the coexistence of superlattice, simple hexagonal lattice and amorphous structures with approximately 100 nm inhomogeneous length scale, consistent with high-resolution transmission electron microscope studies. The atomic-force-microscope-compatible microwave probe is able to perform a quantitative subsurface electrical study in a noninvasive manner. Finally, the phase change memory function in In(2)Se(3) nanoribbon devices can be locally recorded with big signals of opposite signs.

Large anisotropy of electrical properties in layer-structured In2Se3 nanowires.

Layer-structured indium selenide (In 2Se 3) nanowires (NWs) have large anisotropy in both shape and bonding. In 2Se 3 NWs show two types of growth directions: [11-20] along the layers and [0001] perpendicular to the layers. We have developed a powerful technique combining high-resolution transmission electron microscopy (HRTEM) investigation with single NW electrical transport measurement, which allows us to correlate directly the electrical properties and structure of the same individual NWs. The NW devices were made directly on a 50 nm thick SiN x membrane TEM window for electrical measurements and HRTEM study. NWs with the [11-20] growth direction exhibit metallic behavior while the NWs grown along the [0001] direction show n-type semiconductive behavior. Excitingly, the conductivity anisotropy reaches 10 (3)-10 (6) at room temperature, which is 1-3 orders magnitude higher than the bulk ratio.

Void formation induced electrical switching in phase-change nanowires.

Solid-state structural transformation coupled with an electronic property change is an important mechanism for nonvolatile information storage technologies, such as phase-change memories. Here we exploit phase-change GeTe single-nanowire devices combined with ex situ and in situ transmission electron microscopy to correlate directly nanoscale structural transformations with electrical switching and discover surprising results. Instead of crystalline-amorphous transformation, the dominant switching mechanism during multiple cycling appears to be the opening and closing of voids in the nanowires due to material migration, which offers a new mechanism for memory. During switching, composition change and the formation of banded structural defects are observed in addition to the expected crystal-amorphous transformation. Our method and results are important to phase-change memories specifically, but also to any device whose operation relies on a small scale structural transformation.

Chronic urticaria sera increase basophil CD203c expression.

BACKGROUND: Approximately 40% of patients with chronic idiopathic urticaria have antibodies to the alpha subunit of the high-affinity IgE receptor. CD203c is a basophil activation marker known to be upregulated by cross-linking of the FcepsilonRIalpha receptor and may serve as a useful marker to identify these patients. OBJECTIVE: The primary objective was to assess the affect of sera from patients with chronic idiopathic urticaria on basophil CD203c expression. Secondary objectives were to correlate CD203c expression with basophil histamine release and size of the autologous serum skin test and to determine whether the mechanism is mediated by an IgG antibody. METHODS: Sera were obtained from patients with chronic idiopathic urticaria and positive autologous serum skin test or negative autologous serum skin test and normal controls. Sera were incubated with donor whole blood. Activated basophils from whole blood were identified by flow cytometry on the basis of the presence of CD203c on high-expressing IgE positive cells. RESULTS: Incubation of donor basophils with sera from patients with chronic idiopathic urticaria and positive autologous serum skin test demonstrated significant upregulation of CD203c. IgG depletion of representative sera from patients with chronic idiopathic urticaria resulted in significant decrease in CD203c expression on donor basophils. CD203c expression correlated with basophil histamine release and the size of the autologous serum skin test. CONCLUSION: Sera from patients with chronic idiopathic urticaria and positive autologous serum skin test significantly upregulate basophil CD203c and correlate with basophil histamine release. CLINICAL IMPLICATIONS: This article describes an activation marker on basophils whose expression is increased by sera from patients with chronic idiopathic urticaria.