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.

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 also been harnessed to fashion them into compact optical antennas. Here, we take the next important step by realizing 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 an Ag strip that simultaneously serves as a plasmonic resonator and a miniature heating stage.

Bulk and thin films of III-VI and I-III-VI semiconductors such as In 2 Se 3 (IS), 1 CuInSe 2 (CIS) 2 and CuGaSe 2 3 have been actively studied for photovoltaic applications. Among them, polycrystalline thin films of CuIn x Ga 1-x Se 2 (CIGS) have been demonstrated to have a high-power efficiency of 19.2%, 4 which even outperforms the best single crystalline devices. 5 This extraordinary performance was proposed to be caused by a hole energy barrier at grain boundaries for preventing electron-hole recombination, 6,7 although this hypothesis is still under question. 8 In addition, the high efficiency is also attributed to the formation of random p-n junctions distributed in compositionally inhomogeneous polycrystalline thin films. 9 Nanowire (NW) morphology of I-III-VI chalcopyrite materials can provide a well-defined nanoscale domain with clearly identifiable "grain boundaries" for studying these effects. Aligned NWs with a controllable composition modulation can afford ordered p-n junctions and continuous charge carrier transport pathways without deadends, which is an advantage over the random p-n junctions. Therefore, NW solar cells 10 might provide an even higher efficiency. The promise will not be fulfilled without a method for fabricating the required NW structures. Herein, we report the synthesis of IS and CIS single crystalline NWs via a Au-catalyzed vapor-liquid-solid (VLS) growth. We demonstrate the temperature-induced reversible superlattice transformation in IS NWs. We also show that the crystal structure of CIS NWs has dependence on Cu concentration.A solvothermal method was used previously for producing CIS nanowiskers and nanoparticles although their morphology and crystallinity are ill-defined. 11 Solution colloidal synthesis was used to produce AgInSe 2 nanorods and nanoparticles with small aspect ratios less than 5. 12 We exploit a VLS growth [13][14][15] because this method has been shown to be among the most powerful ones for predictably synthesizing single-crystalline NW structures with a size, position, and orientation control.The synthesis of IS and CIS NWs has been carried out in a similar way as that in our previous studies 16 (Supporting Information). In a tube furnace, a carrier gas transports the vapor of R-phase IS or chalcopyrite-type CIS downstream. Gold colloids dispersed on Si substrates were used as VLS catalysts. Typical synthesis conditions are pressure ) 50 Torr, temperature ) 700 °C, time ) 5 h, and gas flow ) 120 sccm. To controllably adjust the Cu

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.

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.

We present omnidirectional near-unity absorption of light in an ultrathin planar semiconductor layer on a metal substrate. Using full-field simulations and a modal analysis, it is shown that more than 98% of the incident light energy can be absorbed in a mere 12 nm thick Ge layer on a Ag substrate at the wavelength of 625 nm over a wide range of angles (80% absorption up to 66° in the transverse magnetic and 67° in the transverse electric polarizations). The physical origin of such remarkable absorption properties is the coupling of incident light to the Brewster mode supported by the structure. The modal dispersion connects several critical coupling points in a dispersion diagram at which the absorption is unity and exhibits a virtually flat dispersion relation for both polarizations, resulting in omnidirectional, near-unity absorption. Potential applications of this simple, planar geometry such as photodetectors and solar cells made from various semiconductor materials are also discussed along with feasible charge-extracting structures and performance estimates.

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 1-5 and chalcogenides 6,7 , these microscopic phases are of great scientific and technological importance for research in hightemperature superconductors 1,2 , colossal magnetoresistance effect 4 , phase-change memories 5,6 , and domain switching operations [7][8][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 10 by near-field scanning microwave impedance microscopy [11][12][13] . Multiple phases with local resistivity spanning six orders of magnitude are identified as the coexistence of superlattice, simple hexagonal lattice and amorphous structures with ~100nm inhomogeneous length scale, consistent with high-resolution transmission electron microscope studies. The atomic-force-microscope-compatible microwave probe is able to perform quantitative sub-surface electronic study in a noninvasive manner. Finally, the phase change memory function in In 2 Se 3 nanoribbon devices can be locally recorded with big signal of opposite signs. 2While the conventional wisdom on solids largely results from the real-space periodic structures and k-space band theories 14 , recent advances in physics have shown clear evidence that microscopic inhomogeneity, manifested as sub-micron spatial variations of the material properties, could indeed occur under certain conditions. Utilizing various probe-sample coupling mechanisms 15 , spatial inhomogeneity has been observed as nanometer gap variations in high-Tc superconductors 1,2 , coexisting electronic states in VO 2 near the metal-insulator transition 3 , ferromagnetic domains in manganites showing colossal magnetoresistance effect 4 , and in an ever-growing list. Probing these non-uniform phases provides not only much knowledge of the underlying interactions, but also valuable information for applications of the domain structures. In particular, spatially resolved properties are of significant interest for phase change and other switching materials to be on board the nanoelectric era [5][6][7][8][9] .While a number of contrast mechanisms 15 have been employed to visualize the electronic inhomogeneity, established scanning probe techniques do not directly access the low-frequency (f) complex permittivity ε(ω) = ε′ + iσ/ω, where ε′ is the dielectric constant and σ the conductivity, which holds a special position to study the ground state properties of materials. For local electrodynamic response, near-field technique is imperative to resolve spatial variations at length scales well below the radiation wavelength 16 . For this study, the working frequency is set at ~1GHz, i.e., in the microwave regime, to stay below resonant excitation...

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