Silver Nanowire-Based Transparent Electrodes for V2O5 Thin Films with Electrochromic Properties.

The development of electrochromic systems, known for the modulation of their optical properties under an applied voltage, depends on the replacement of the state-of-the-art ITO (In2O3:Sn) transparent electrode (TE) as well as the improvement of electrochromic films. This study presents an innovative ITO-free electrochromic film architecture utilizing oxide-coated silver nanowire (AgNW) networks as a TE and V2O5 as an electrochromic oxide layer. The TE was prepared by simple spray deposition of AgNWs that allowed for tuning different densities of the network and hence the resistance and transparency of the film. The conformal oxide coating (SnO2 or ZnO) on AgNWs was deposited by atmospheric-pressure spatial atomic layer deposition, an open-air fast and scalable process yielding a highly stable electrode. V2O5 thin films were then deposited by radio frequency magnetron sputtering on the AgNW-based TE. Independent of the oxide's nature, a 20 nm protective layer thickness was insufficient to prevent the deterioration of the AgNW network during V2O5 deposition. On the contrary, crystalline V2O5 films were grown on 30 nm thick ZnO or SnO2-coated AgNWs, exhibiting a typical orange color. Electrochromic characterization demonstrated that only V2O5 films deposited on 30 nm thick SnO2-coated AgNW showed characteristic oxidation-reduction peaks in the Li+-based liquid electrolyte associated with a reversible orange-to-blue color switch for at least 500 cycles. The electrochromic key properties of AgNW/SnO2 (30 nm)/V2O5 films are discussed in terms of structural and morphological changes due to the AgNW network and the nature and thickness of the two protective oxide coatings.

Conductive carbon paint: An efficient way to electrodeposit metallic nanowires by using porous membranes.

The present work demonstrates that conductive carbon paint, used for sample preparation in electron microscopy, can be a more straightforward and as-effective substitute for the metallic layer deposition usually used for the electrodeposition of metallic nanowires within porous membranes. AFM images demonstrated the good surface quality of the carbon layer. Raman spectroscopy confirmed the high crystallinity of carbon and high density of π-electrons. The electrical conductivity of the carbon layer was estimated using the linear sweep voltammetry technique. This new cathode was employed to grow continuous (Ni) and composition-modulated (Ni/Cu) nanowires within alumina templates, starting from aqueous solutions of Ni2+ and Cu2+ mixed salts. The obtention of metallic copper and nickel, and their separation can be readily observed by scanning electron microscopy and elemental mapping by EDS.

Second-Order Photoinduced Reflectivity for Retrieval of the Dynamics in Plasmonic Nanostructures.

Measuring the change in reflectivity (ΔR) using the traditional pump-probe approach can monitor photoinduced ultrafast dynamics in matter, yet relating these dynamic to physical processes for complex systems is not unique. By applying a simple modification to the classical pump-probe technique, we simultaneously measure both the first and second order of ΔR. These additional data impose new constraints on the interpretation of the underlying ultrafast dynamics. In the first application of the approach, we probe the dynamics induced by a pump laser on the local-surface plasmon resonance (LSPR) in gold nanoantennas. Measurements of ΔR over several picoseconds and a wide range of probe wavelengths around the LSPR peak are followed by data fitting using the two-temperature model. The constraints, imposed by the second-order data, lead us to modify the model and force us to include the contribution of nonthermalized electrons in the early stages of the dynamics.

Fundamental frequency analysis of endohedrally functionalized carbon nanotubes with metallic nanowires: a molecular dynamics study.

The endohedral functionalization of carbon nanotubes (CNTs) with nanowires (NWs), i.e., NWs@CNTs, has been the center of attention in a lot of research due to the applications of NWs@CNTs in nanoelectronic devices, heterogeneous catalysis, and electromagnetic wave absorption. To this end, based on the classical molecular dynamics (MD) simulations, the effect of four pentagonal structures of encapsulated metallic nanowires (mNWs), namely the eclipsed pentagon (E), the deformed staggered pentagon (Ds), staggered pentagon (S), and staggered pentagonal structure without the monatomic chain passing through the centers of the parallel pentagons (R) configurations on the vibrational behavior of CNTs, is investigated. Also, the effects of geometrical parameters such as length and radius of CNTs on the natural frequencies of simulated models are explored. The results illustrate that by increasing the length, the natural frequency of pure CNTs and mNWs@CNTs decreases. In a similar length, mNWs@CNTs possess lower natural frequencies compared to the pure CNTs. According to the results, the highest and lowest natural frequencies are calculated by inserting the S structure of sodium NW and Ds structure of aluminum NW inside their proper armchair CNT, i.e., Na-S NW@ (9,9) CNT and Al-Ds NW@ (7,7) CNT, respectively.

Transparent and Mechanically Resistant Silver-Nanowire-Based Low-Emissivity Coatings.

This article reports on the fabrication and investigation of low-emissivity (low-E) coatings based on random networks of silver nanowires (AgNWs). The transparent layers based on AgNWs do exhibit low emissivity while being still transparent: an overall emissivity as low as 0.21 at 78% total transmittance was obtained. A simple physical model allows to rationalize the emissivity-transparency dependence and a good agreement with experimental data is observed. This model demonstrates the role played by AgNWs which partially reflect IR photons emitted by the substrate, exacerbating then the presence of AgNWs and lowering the total emissivity. The potential use of such layers in functional devices is hampered by the poor intrinsic surface adhesion of the AgNWs, which renders the coating fragile and prone to mechanical damaging. Two very efficient encapsulation processes based on the deposition of a conformal alumina thin film using the spatial atomic layer deposition technique and the solution processed layer deposition of a polysiloxane varnish have been developed to thwart this weakness. Both coatings combine sturdy mechanical resistance relying on a strong interfacial adhesion and excellent optical transmittance properties. The performances for the mechanically resistant low-E coatings achieve an overall emissivity as low as 0.34 at 74% total transparency. The set of optical properties and mechanical resistance of the reported AgNWs based low-E coatings combined with the ease of fabrication and the cost-effective production process make it an excellent candidate for a wide set of applications, including smart windows for energy-saving buildings.

Interfacing Neurons with Nanostructured Electrodes Modulates Synaptic Circuit Features.

Understanding neural physiopathology requires advances in nanotechnology-based interfaces, engineered to monitor the functional state of mammalian nervous cells. Such interfaces typically contain nanometer-size features for stimulation and recording as in cell-non-invasive extracellular microelectrode arrays. In such devices, it turns crucial to understand specific interactions of neural cells with physicochemical features of electrodes, which could be designed to optimize performance. Herein, versatile flexible nanostructured electrodes covered by arrays of metallic nanowires are fabricated and used to investigate the role of chemical composition and nanotopography on rat brain cells in vitro. By using Au and Ni as exemplary materials, nanostructure and chemical composition are demonstrated to play major roles in the interaction of neural cells with electrodes. Nanostructured devices are interfaced to rat embryonic cortical cells and postnatal hippocampal neurons forming synaptic circuits. It is shown that Au-based electrodes behave similarly to controls. Contrarily, Ni-based nanostructured electrodes increase cell survival, boost neuronal differentiation, and reduce glial cells with respect to flat counterparts. Nonetheless, Au-based electrodes perform superiorly compared to Ni-based ones. Under electrical stimulation, Au-based nanostructured substrates evoke intracellular calcium dynamics compatible with neural networks activation. These studies highlight the opportunity for these electrodes to excite a silent neural network by direct neuronal membranes depolarization.

Multifunctional Metallic Nanowires in Advanced Building Applications.

Metallic nanowires (NWs) have attracted great attention in the frontiers of nanomaterial science due to their extraordinary properties, such as high thermal and electrical conductivity, high aspect ratio, good mechanical flexibility, and excellent optical transparency. The metallic NWs and their nanocomposites, as a promising alternative for conventional building materials, have been extensively studied recently, but review works on these novel versatile nanostructures and their various uses in the building and construction industry are still lacking. We present a comprehensive review on current state-of-the-art research and progress regarding multifunctional metallic NWs and their specific building applications, including thermal energy storage (TES), thermal transport, electrochromic windows (ECW), as well as photovoltaic (PV) cells. The nanosynthesis techniques and nanocharacterization of silver nanowires (AgNWs) and copper nanowires (CuNWs) are overviewed and compared with each other. In addition, the fundamentals of different NWs for advanced building applications are introduced. Further discussion is presented on the improved performance of base materials by using these nanostructures, highlighting the key factors exhibiting their superior performance. Finally, the key benefits and limitations of metallic NWs for new generation building materials are obtained.

New Trends in the Simulation of Nanosplasmonic Optical D-Type Fiber Sensors.

This article presents a review of the numerical techniques employed in simulating plasmonic optical sensors based on metal-dielectric nanostructures, including examples, ranging from conventional D-type fiber sensors, to those based on photonic crystal D-type fibers and incorporating metamaterials, nanowires, among other new materials and components, results and applications. We start from the fundamental physical processes, such as optical and plasmonic mode coupling, and discuss the implementation of the numerical model, optical response customization and their impact in sensor performance. Finally, we examine future perspectives.

Room-Temperature-Processable Wire-Templated Nanoelectrodes for Flexible and Transparent All-Wire Electronics.

Sophisticated preparation of arbitrarily long conducting nanowire electrodes on a large area is a significant requirement for development of transparent nanoelectronics. We report a position-customizable and room-temperature-processable metallic nanowire (NW) electrode array using aligned NW templates and a demonstration of transparent all-NW-based electronic applications by simple direct-printing. Well-controlled electroless-plating chemistry on a polymer NW template provided a highly conducting Au NW array with a very low resistivity of 7.5 µΩ cm (only 3.4 times higher than that of bulk Au), high optical transmittance (>90%), and mechanical bending stability. This method enables fabrication of all-NW-based electronic devices on various nonplanar surfaces and flexible plastic substrates. Our approach facilitates realization of advanced future electronics.

Electrochemical detectors based on carbon and metallic nanostructures in capillary and microchip electrophoresis.

Carbon and metallic-based nanostructures have been progressively implemented as innovative electrochemical detectors in CE and microchip electrophoresis (ME). For both type of nanomaterials and toward selected examples, this review details the impact of these nanomaterials for enhanced detection performance in CE, ME, and paper-based microfluidic devices. The analytical performance and the analytical potential in real world applications is also presented and discussed.

Metallic Nanowire-Based Transparent Electrodes for Next Generation Flexible Devices: a Review.

Transparent electrodes attract intense attention in many technological fields, including optoelectronic devices, transparent film heaters and electromagnetic applications. New generation transparent electrodes are expected to have three main physical properties: high electrical conductivity, high transparency and mechanical flexibility. The most efficient and widely used transparent conducting material is currently indium tin oxide (ITO). However the scarcity of indium associated with ITO's lack of flexibility and the relatively high manufacturing costs have a prompted search into alternative materials. With their outstanding physical properties, metallic nanowire (MNW)-based percolating networks appear to be one of the most promising alternatives to ITO. They also have several other advantages, such as solution-based processing, and are compatible with large area deposition techniques. Estimations of cost of the technology are lower, in particular thanks to the small quantities of nanomaterials needed to reach industrial performance criteria. The present review investigates recent progress on the main applications reported for MNW networks of any sort (silver, copper, gold, core-shell nanowires) and points out some of the most impressive outcomes. Insights into processing MNW into high-performance transparent conducting thin films are also discussed according to each specific application. Finally, strategies for improving both their stability and integration into real devices are presented.

Direct Imaging of the Onset of Electrical Conduction in Silver Nanowire Networks by Infrared Thermography: Evidence of Geometrical Quantized Percolation.

Advancement in the science and technology of random metallic nanowire (MNW) networks is crucial for their appropriate integration in many applications including transparent electrodes for optoelectronics and transparent film heaters. We have recently highlighted the discontinuous activation of efficient percolating pathways (EPPs) for networks having densities slightly above the percolation threshold. Such networks exhibit abrupt drops of electrical resistance when thermal or electrical annealing is performed, which gives rise to a "geometrically quantized percolation". In this Letter, lock-in thermography (LiT) is used to provide visual evidence of geometrical quantized percolation: when low voltage is applied to the network, individual "illuminated pathways" can be detected, and new branches get highlighted as the voltage is incrementally increased. This experimental approach has allowed us to validate our original model and map the electrical and thermal distributions in silver nanowire (AgNW) networks. We also study the effects of electrode morphology and wire dimensions on quantized percolation. Furthermore, we demonstrate that the network failure at high temperature can also be governed by a quantized increase of the electrical resistance, which corresponds to the discontinuous destruction of individual pathways (antipercolation). More generally, we demonstrate that LiT is a promising tool for the detection of conductive subclusters as well as hot spots in AgNW networks.

Structural transitions in electron beam deposited Co-carbonyl suspended nanowires at high electrical current densities.

Suspended nanowires (SNWs) have been deposited from Co-carbonyl precursor (Co2(CO)8) by focused electron beam induced deposition (FEBID). The SNWs dimensions are about 30-50 nm in diameter and 600-850 nm in length. The as-deposited material has a nanogranular structure of mixed face-centered cubic (FCC) and hexagonal close-packed (HCP) Co phases, and a composition of 80 atom % Co, 15 atom % O and 5 atom % C, as revealed by transmission electron microscopy (TEM) analysis and by energy-dispersive X-ray (EDX) spectroscopy, respectively. Current (I)-voltage (V) measurements with current densities up to 10(7) A/cm(2) determine different structural transitions in the SNWs, depending on the I-V history. A single measurement with a sudden current burst leads to a polycrystalline FCC Co structure extended over the whole wire. Repeated measurements at increasing currents produce wires with a split structure: one half is polycrystalline FCC Co and the other half is graphitized C. The breakdown current density is found at 2.1 × 10(7) A/cm(2). The role played by resistive heating and electromigration in these transitions is discussed.

Strong Hall-Petch Type Behavior in the Elastic Strain Limit of Nanotwinned Gold Nanowires.

Pushing the limits of elastic deformation in nanowires subjected to stress is important for the design and performance of nanoscale devices from elastic strain engineering. Particularly, introducing nanoscale twins has proved effective in rising the tensile strength of metals. However, attaining ideal elastic strains in nanotwinned materials remains challenging, because nonuniform twin sizes locally affect the yielding behavior. Here, using in situ high-resolution transmission electron microscopy tensile testing of nanotwinned [111]-oriented gold nanowires, we report direct lattice-strain measurements that demonstrate a strong Hall-Petch type relationship in the elastic strain limit up to 5.3%, or near the ideal theoretical limit, as the twin size is decreased below 3 nm. It is found that the largest twin in nanowires with irregular twin sizes controls the slip nucleation and yielding processes in pure tension, which is in agreement with earlier atomistic simulations. Continuous hardening behavior without loss of strength or softening is observed in nanotwinned single-crystalline gold nanowires, which differs from the behaviors of bulk nanocrystalline and nanotwinned-nanocrystalline metals. These findings are of practical value for the use of nanotwinned metallic and semiconductor nanowires in strain-engineered functional microdevices.

Personal thermal management by metallic nanowire-coated textile.

Heating consumes large amount of energy and is a primary source of greenhouse gas emission. Although energy-efficient buildings are developing quickly based on improving insulation and design, a large portion of energy continues to be wasted on heating empty space and nonhuman objects. Here, we demonstrate a system of personal thermal management using metallic nanowire-embedded cloth that can reduce this waste. The metallic nanowires form a conductive network that not only is highly thermal insulating because it reflects human body infrared radiation but also allows Joule heating to complement the passive insulation. The breathability and durability of the original cloth is not sacrificed because of the nanowires' porous structure. This nanowire cloth can efficiently warm human bodies and save hundreds of watts per person as compared to traditional indoor heaters.