Conductivity Of Nanowires Research Articles

Tuning Thermal Conductivity in Si Nanowires with Patterned StructuresSupported by the National Natural Science Foundation of China (Grant No. 11875047).

Tuning the thermal conductivity of silicon nanowires (Si-NWs) is essential for realization of future thermoelectric devices. The corresponding management of thermal transport is strongly related to the scattering of phonons, which are the primary heat carriers in Si-NWs. Using the molecular dynamics method, we find that the scattering of phonons from internal body defects is stronger than that from surface structures in the low-porosity range. Based on our simulations, we propose the concept of an exponential decay in thermal conductivity with porosity, specifically in the low-porosity range. In contrast, the thermal conductivity of Si-NWs with a higher porosity approaches the amorphous limit, and is insensitive to specific phonon scattering processes. Our findings contribute to a better understanding of the tuning of thermal conductivity in Si-NWs by means of patterned nanostructures, and may provide valuable insights into the optimal design of one-dimensional thermoelectric materials.

α-FeOOH nanowires loaded on carbon paper anodes improve the performance of microbial fuel cells

Nanowires synthesized from metal oxides exhibit better conductivity than nanoparticles due to their greater aspect ratio which means that they can transmit electrons over longer distances; in addition, they are also more widely available than pili because their synthesis is not affected by the bacteria themselves. However, there is still little research on the application of metal oxides nanowires to enhance power generation of microbial fuel cells (MFC). In this study, a simple hydrothermal synthesis method was adopted to synthesize α-FeOOH nanowires on carbon paper (α-FeOOH-NWs), which serve as an anode to explore the mechanism of power generation enhancement of MFC. Characterization results reveal α-FeOOH-NWs on carbon paper are approximately 30–50 nm in diameter, with goethite structure. Electrochemical test results indicate that α-FeOOH nanowires could enhance the electrochemical activity of carbon paper and reduce the electron transfer resistance (Rct). Furthermore, α-FeOOH-NWs made the power density of MFC 3.2 times of the control device. SEM result demonstrates that nanowires are beneficial to the formation of biofilms and increase biomass on the electrode surface. Our results demonstrate that nanowires not only improve the electrochemical activity and conductivity of carbon paper but also facilitate the formation of biofilms and increase the biomass of the anode surface. These two mechanisms work together to boost extracellular electron transfer and power generation efficiency of MFC with α-FeOOH-NWs. Our study provides further evidence for the electrical conductivity of metal nanowires, promoting their potential applications in electricity generation such as MFC or other energy development fields.

Three-terminal nonlocal conductance in Majorana nanowires: Distinguishing topological and trivial in realistic systems with disorder and inhomogeneous potential

We develop a theory for the three-terminal nonlocal conductance in Majorana nanowires as existing in the superconductor-semiconductor hybrid structures in the presence of superconducting proximity, spin-orbit coupling, and Zeeman splitting. The key question addressed is whether such nonlocal conductance can decisively distinguish between trivial and topological Majorana scenarios in the presence of chemical potential inhomogeneity and random impurity disorder. We calculate the local electrical as well as nonlocal electrical and thermal conductance of the pristine nanowire (good zero-bias conductance peaks), the nanowire in the presence of quantum dots and inhomogeneous potential (bad zero-bias conductance peaks), and the nanowire in the presence of large disorder (ugly zero-bias conductance peaks). The local conductance by itself is incapable of distinguishing the trivial states from the topological states since zero-bias conductance peaks are generic in the presence of disorder and inhomogeneous potential. The nonlocal conductance, which in principle is capable of providing the bulk gap closing and reopening information at the topological quantum phase transition, is found to be far too weak in magnitude to be particularly useful in the presence of disorder and inhomogeneous potential. Therefore, we focus on the question of whether the combination of the local, nonlocal electrical, and thermal conductance can separate the good, bad, and ugly zero-bias conductance peaks in finite-length wires. Our paper aims to provide a guide to future experiments, and we conclude that a combination of all three measurements would be necessary for a decisive demonstration of topological Majorana zero modes in nanowires---positive signals corresponding to just one kind of measurements are likely to be false positives arising from disorder and inhomogeneous potential.

Super wear-resistant and conductive cotton fabrics based on sliver nanowires

To investigate the effect of linear, rod and granular nano-silver structures on the electrical conductivity and wear resistance of cotton fabrics, silver nanowires (AgNWs), silver nano-rods (AgNRs) and silver nanoparticles (AgNPs) were separately obtained by solvothermal method, and then adsorbed on the cotton fabrics. Compared with AgNRs and AgNPs that silver nanowires could form network structure on the cotton fabrics. As the ratio of nano-sliver length to diameter increases, the effective adsorption mass of nano-sliver on the cotton increases, improving the conductivity of the textile electrode. No matter how many times of rubbing, it had no effect on the square resistance of the AgNWs/cotton. The cotton fabrics treated with silver nanowires had the best performances and wear resistance.

High Current Field Emission from Large-Area Indium Doped ZnO Nanowire Field Emitter Arrays for Flat-Panel X-ray Source Application.

Large-area zinc oxide (ZnO) nanowire arrays have important applications in flat-panel X-ray sources and detectors. Doping is an effective way to enhance the emission current by changing the nanowire conductivity and the lattice structure. In this paper, large-area indium-doped ZnO nanowire arrays were prepared on indium-tin-oxide-coated glass substrates by the thermal oxidation method. Doping with indium concentrations up to 1 at% was achieved by directly oxidizing the In-Zn alloy thin film. The growth process was subsequently explained using a self-catalytic vapor-liquid-solid growth mechanism. The field emission measurements show that a high emission current of ~20 mA could be obtained from large-area In-doped sample with a 4.8 × 4.8 cm2 area. This high emission current was attributed to the high crystallinity and conductivity change induced by the indium dopants. Furthermore, the application of these In-doped ZnO nanowire arrays in a flat-panel X-ray source was realized and distinct X-ray imaging was demonstrated.

Thermal conductivity and electrical resistivity of single copper nanowires.

Copper nano-interconnects are ubiquitous in semiconductor devices. The electrical and thermal properties of copper nanowires (CuNWs) profoundly affect the performance of electronics. In contrast to the intensively studied electrical properties of CuNWs, the thermal conductivities of CuNWs have seldom been examined. In this study, the electrical resistivity and thermal conductivity of single CuNWs were investigated. The Bloch-Grüneisen formula was introduced to determine the mechanisms responsible for the obtained electrical resistivity of the CuNWs. High residual resistivity was found, which indicated strong structural scattering on the electron transport resulting from defect scattering and boundary scatterings at the copper-copper oxide interface and grain boundaries. The mean structural scattering distance was employed to appreciate the degree of structural scattering in the CuNWs. The residual resistivity and electron-phonon coupling parameter were found to increase with the degree of structural scattering. Moreover, the unified thermal resistivity was introduced to illustrate the mechanisms responsible for the CuNWs' thermal conductivities. Similarly, large values of residual unified thermal resistivity and electron-phonon-induced unified thermal resistivity were found. The obtained unified thermal resistivities of the CuNWs could also be qualitatively explained by the degree of structural scattering in the CuNWs. The results suggested that structural scattering was predominant in the electrical current transport and heat transfer in the nanowires. This study revealed the mechanisms of electrical resistivity and thermal conductivity of CuNWs, and the insights could assist in improving the design of semiconductor architectures.

Electron Conduction Channel of Silver Nanowire Modified TiO₂ Photoanode for Improvement of Interface Impedance of Dye-Sensitized Solar Cell

In this article, novel double-layer films were designed and examined for dye-sensitized solar cells (DSSCs). The commercial titanium dioxide (TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) nanoparticles as a bonding underlayer, and the silver nanowires (AgNWs) were used and prepared by means of the polyol method. They which were doped into TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> composite materials. The microstructure of AgNWs and the effect of modified DSSCs on photovoltaic (PV) performance were examined. The experimental research indicated that the localized surface plasmon resonance (LSPR) could enhance light-harvesting efficiency. The exceptional electrical conductivity of silver nanowires also improved the interface resistance of DSSCs. We found that LSPR could substantially boost the incident photon-to-electron conversion efficiency (IPCE) of such DSSCs. The AgNWs@TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (an optimized content of 3 wt% in photoanode) improved the photovoltaic conversion efficiency (η) of the DSSCs from 4.01% to 5.88%, when compared with the DSSCs without AgNWs@TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (pure TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ).

Nonlocal heat conduction in silicon nanowires and carbon nanotubes

Experimental results showed that the effective thermal conductivity of silicon nanowire is smaller than the bulk thermal conductivity, while that of carbon nanotube (CNT) is usually much larger than its bulk counterpart. In order to resolve this paradox, a nonlocal heat conduction model for one-dimensional materials is proposed. This nonlocal model indicates that the different heat conduction boundary conditions of silicon nanowire and CNT lead to the different behaviour of their thermal conductivities in comparison with their bulk counterparts. Furthermore, the nonlocal effect of heat flux on the surfaces of the CNT makes the thermal conductivity of the single-wall CNT more than seven orders of magnitude higher than its bulk thermal conductivity. The thermal conductivities of the single-wall and multi-wall CNTs obtained by using the nonlocal model show an agreement with the experimental ones.

Highly thermally stable and flexible conductive film electrodes based on photo-responsive shape memory polyimide

Conductive polyimide (PI) film electrodes, which combine the electrical conductivity of silver nanowires (AgNWs) with multi-stimulus response properties, are promising for smart devices, such as actuators, remote sensing circuits, intelligent garments, and smart flexible robots. The flexible electrodes are fabricated using shape memory polyimide as the substrate. In addition, a thermally cured liquid photopolymer, SR 368D, was used as a transition layer and AgNWs served as the conductive layer (denoted as AgNW/SR/PI electrode). The AgNW/SR/PI electrodes exhibited a low resistivity of ∼1.3 Ω sq−1 because of the high conductivity of the AgNWs. Integrating the high strength of PI films with AgNWs gave the electrodes highly conductive and stable properties. The electrodes were able to maintain a low resistivity of ∼1.5 Ω sq−1 even after 2000 bending/unbending cycles and retained ∼1.8 Ω sq−1 after 2000 adhesion/peeling cycles. Moreover, the AgNW possessed conductivity and infrared absorption, and the flexible electrodes recovered the initial shape under the effects of Joule heating and photo-thermal trigger by an electric stimulus and photo stimulus.

Conductive elastic sponge-based triboelectric nanogenerator (TENG) for effective random mechanical energy harvesting and ammonia sensing

Abstract Triboelectric nanogenerator (TENG) based on elastic materials is increasing interests for irregular and random mechanical energies harvesting. However, the conductive design of the elastic materials in TENGs often limits its applications. Herein, a new conductive and elastic sponge-based triboelectric nanogenerator (ES-TENG) is developed for random mechanical energy harvesting, which integrates the elastic material and the conductive material on a flexible sponge to realize the collection of mechanical energies, particularly for irregular and random motions. The conductive elastic sponge is prepared by a simple dilute chemical polymerization of aniline to grow conductive polyaniline nanowires (PANI NWs) on the surface of elastic sponge. Due to the flexible deformation of sponge, it can harvest the kinetic energy of disordered motion with different amplitudes and from variable directions. As the triboelectric layer of ES-TENG, the porous sponge and polyaniline nanowires on its surface can provide a large contact area and improve the triboelectric efficiency. At the same time, the conductive polyaniline coating on the surface of sponge can also be used as the electrode of ES-TENG to conduct electrons and generate an output of 540 V and 6 μA respectively, which can be used on various flexible object surfaces to collect irregular and random mechanical energy ubiquitous in daily life. In addition, based on the NH3-sensing performance and the three-dimensional reticular structure of the polyaniline nanowires on the elastic sponge, the ES-TENG can make it work as self-powered sensor for detecting toxic NH3 with the detection limit up to 1 ppm and the response time less than 3 s. In view of the microporous and nanowire structures, elasticity, conductivity and easy fabrication of the conductive elastic sponge, the ES-TENG has promising applications in various irregular and random mechanical energy harvesting and self-powered NH3 sensors.

Width-induced metal–insulator transition in SrVO3 lateral nanowires spontaneously formed on the ultrathin film

We investigated lateral nanowires at the topmost layer of SrVO3 (001) ultrathin films using in situ low-temperature scanning tunneling microscopy and spectroscopy. The nanowires were spontaneously formed in the topmost layer of SrVO3 with a (√2 × √2)-R45° reconstruction on the terrace of a (√5 × √5)-R26.6° reconstruction. The electronic states of nanowires were significantly influenced by the nanowire width. With reducing the nanowire width from 5.5 nm to 1.7 nm, the zero-bias conductance of nanowires steeply decreased toward zero, exhibiting a metal–insulator transition possibly driven by dimensional crossover, previously observed in thickness-reduced SrVO3 ultrathin films.

Pseudocapacitance of chemically stable MnO2-NiO mixture layer on highly conductive Sb doped SnO2 nanowire arrays

We report the electrochemical properties of MnO2–NiO mixture layer that is coated on highly conductive SnO2 nanowires. In this study, the effect of the nanowire conductivity and coating composition on the pseudocapacitic performance was systematically examined. To control the electric conductivity of the nanowire, Sb was doped into SnO2 during vapor–liquid-solid (VLS) process. Subsequently, pure or NiO added MnO2 layer was electrochemically deposited on SnO2 nanowire arrays. Structural studies show that the electrodeposition layer uniformly and conformally covered the nanowires. Low concentration Sb doping (up to 5 at%) increases the electric conductivity of the nanowires which work as an electron transport layer of the pseudocapacitor. Electrochemical studies indicate that the addition of NiO to MnO2 promotes a charging/discharging process through Faraday reaction by changing the oxidation mechanism of MnO2. These results guide a design of the metal oxide mixture for the pseudocapacitor application.

Range Determination of the Influence of Carrier Concentration on Lattice Thermal Conductivity for Bulk Si and Nanowires

Mathematical modeling has been extended to simulate some physical systems to calculate some parameters that may need a sophisticated cost or may have some obstacles to be measured directly with an experimental method. In this study, the Modified Callaway Model has been used to calculate size dependence lattice thermal conductivity (LTC), and the influence of carrier concentration for bulk Si and its nanowires (NWs) with diameters of 22, 37, 56, and 115 nm has been investigated. Calculations were performed from 3K to 1600K for all cases. The effects of carrier concentration on LTC has found to begin from (1016 cm-1) for the bulk state and that increased to (1024 cm-1) for the NW with a diameter of 22 nm. The temperature that the maximum effect of carrier concentration can occur, has found to be at (10 K) for the bulk, and that increased to (340 K) for the (22 nm) Si NW.

Monte Carlo simulations for understanding the transport properties of metallic nanowires

We report the conductance calculation of metallic nanowires of different metals under the application of a tensile force. The elongation induced by the tensile force was simulated by means of the canonical Monte Carlo method combined with the embedded atom method to compute the energy of the system. We studied nanowires composed of Ag, Au, Pt and Cu. The conductance was calculated by means of the Landauer formula and the non-equilibrium Green function formalism. As previously verified experimentally and using other simulation techniques, the conductance is quantized. In addition to this, we have found that there is a strong correlation between the magnitude of the conductance and the width of the nanowire at its thinnest point. Conductance histograms were analyzed for all the different metals. • Conductance of metallic nanowires was calculated. • The nanowires were simulated by canonical Monte Carlo methods. • The relationship between the quantized conductance and the width was studied. • Conductance histograms were analyzed.

Synthesis dynamics of silver nanowires galvanically displaced by platinum salts: a fabrication route for oxygen reduction electrocatalysts and metal electrodeposition electrodes

The advancement of conductive and flexible thin films is relevant to an assortment of energy applications ranging from organic photovoltaics, fuel cells, lithium ion batteries, and dynamic windows. Here, we develop an inexpensive, fast, and adjustable method to yield nanowire arrays on flexible polyethylene terephthalate substrates for the alkaline oxygen reduction reaction and for reversible metal electrodeposition. Ag nanowires serve as a non-sacrificial template for Pt deposition and allow for the synthesis of bimetallic Pt/Ag nanowires. When not properly controlled, the galvanic displacement reaction occurring at the solid–liquid interface between Ag nanowires and aqueous Pt ions results in nonuniform nucleation and growth profiles, which creates micron-sized gaps in the nanowire arrays. These gaps, which result in poorly conducting thin films, increase in prevalence when immersion length and Pt concentration are increased. Multiple cycles of 10-min immersions in 10 mM K2PtCl4 yield bimetallic Pt/Ag nanowires that maintain the high aspect ratios and conductivities of the initial Ag nanowires, while the added Pt improves electrocatalytic performance and electrochemical durability.

NiMoO4 nanowires supported on Ni/C nanosheets as high-performance cathode for stable aqueous rechargeable nickel-zinc battery

Nickel-based oxides for aqueous rechargeable nickel-zinc (denoted as Ni//Zn) batteries typically suffer from the low capacity and inferior stability due to their slow electron/ion transportation rate and poor electrochemical reversibility. Here, we rationally design a free-standing Ni/C nanosheets (NC) from Ni metal-organic framework as conductive scaffold for NiMoO4 nanowires (NiMoO4-NC), achieving exceptionally high capacity and rate capability. Furthermore, with the use of a new MoO42−-based electrolyte, a stable aqueous Ni//Zn battery with impressive electrochemical performance is also demonstrated based on this NiMoO4-NC cathode. Experimental results reveal that the NC skeleton can dramatically improve the conductivity and ion diffusion rate of the NiMoO4 nanowires, while the addition of MoO42− into electrolyte can effectively suppress the dissolution and structural destruction of NiMoO4 nanowires. As a consequence, a remarkable capacity (229.2 mAh g−1 at 3.4 A g−1) and excellent durability (85.9% capacity retention after 3000 cycles) are delivered by this Ni//Zn battery, outperforming most reported Ni//Zn batteries. Also, this Ni//Zn battery displays an admirable energy density of 407.8 Wh kg−1, together with a remarkable power density of 18.1 kW kg−1, which is of great significance for future electronic application.

Ultra-low thermal conductivity of roughened silicon nanowires: Role of phonon-surface bond order imperfection scattering**Project supported by the National Natural Science Foundation of China (Grant No. 11874145).

The ultra-low thermal conductivity of roughened silicon nanowires (SiNWs) can not be explained by the classical phonon–surface scattering mechanism. Although there have been several efforts at developing theories of phonon–surface scattering to interpret it, but the underlying reason is still debatable. We consider that the bond order loss and correlative bond hardening on the surface of roughened SiNWs will deeply influence the thermal transport because of their ultra-high surface-to-volume ratio. By combining this mechanism with the phonon Boltzmann transport equation, we explicate that the suppression of high-frequency phonons results in the obvious reduction of thermal conductivity of roughened SiNWs. Moreover, we verify that the roughness amplitude has more remarkable influence on thermal conductivity of SiNWs than the roughness correlation length, and the surface-to-volume ratio is a nearly universal gauge for thermal conductivity of roughened SiNWs.

Impact of Polymer-Constrained Annealing on the Properties of DNA Origami-Templated Gold Nanowires.

DNA origami-templated fabrication enables bottom-up fabrication of nanoscale structures from a variety of functional materials, including metal nanowires. We studied the impact of low-temperature annealing on the morphology and conductance of DNA-templated nanowires. Nanowires were formed by selective seeding of gold nanorods on DNA origami and gold electroless plating of the seeded structures. At low annealing temperatures (160 °C for seeded-only and 180 °C for plated), the wires broke up and separated into multiple, isolated islands. Through the use of polymer-constrained annealing, the island formation in plated wires was suppressed up to annealing temperatures of 210 °C. Four-point electrical measurements showed that the wires remained conductive after a polymer-constrained annealing at 200 °C.

Thermal conductivity of one-dimensional organic nanowires: effect of mass difference phonon scattering

We report the thermal conductivity of π-stacked metallophthalocyanine nanowires using the thermal bridge method. In the temperature range of 20–300 K, the thermal conductivity of copper phthalocyanine nanowires (CuPc NWs) and iron phthalocyanine nanowires (FePc NWs) increases with temperature and reaches a peak value at around T = 40 K, then decreases at a higher temperature following T−1 behavior. For three FePc NWs, the peak values are 7.1 ± 1.21, 8.3 ± 1.33, and 7.6 ± 1.42 Wm−1 K−1, respectively. The peak thermal conductivity is 6.6 ± 0.67 and 6.6 ± 0.51 Wm−1 K−1 for the two CuPc nanowires. The thermal conductivity of FePc NWs is slightly larger than that of CuPc NWs, which is believed to result from the different mass of metal atoms in the phthalocyanine centers, indicating a phonon mass-difference scattering effect. Meanwhile, the thermal contact conductance of the FePc-Pt interface is measured, which will benefit from a better understanding of the thermal transport across dissimilar interfaces.

Role of geometry and surface roughness in reducing phonon mean free path and lattice thermal conductivity of modulated nanowires

Phonon transport simulations were performed to investigate the effects of geometry and surface roughness on the thermal conductivity of modulated nanowires. The finite volume method and ray tracing method were utilized to determine the phonon mean free path. The simulation results showed that the mean free path of the nanowire can be reduced by fabricating intricate structures under a constant ratio of surface area to volume. Then the specularity of the parts of the surfaces of the modulated nanowires was tuned. The simulations revealed that the impact of the specularity on the mean free path depends on the location of the surface whose specularity was tuned; in particular, the mean free path was sensitive to the specularity of the surfaces of neck parts but insensitive to that of other parts. Finally, the thermal conductivity was evaluated by using the simulated mean free path and other phonon transport properties obtained from first-principle calculations. It was found that optimization of the geometry and surface roughness can reduce sufficiently large thermal conductivities; this effect is beneficial in some semiconductor devices.