Resistance Of Nanowires Research Articles

One-pot synthesis of copper nanowire decorated by reduced graphene oxide with excellent oxidation resistance and stability

It is crucial to enhance anti-oxidation resistance of copper nanowires (Cu NWs) without degrading their transparent conductive characteristics. Here, reduced graphene oxide/copper nanowires (RGO/Cu NWs) with coating nanostructures were synthesized by a facile one-pot hydrothermal method. The copper nanowire was prepared by using copper (I) chloride as the precursor while the graphene oxide (GO) was reduced using the polyols as the reducing agent in order to obtain the coating structure, abandoning conventional tedious multi-step preparation processes. The microstructure and morphology of RGO/Cu NWs were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected-area electronic diffraction (SEAD) and X-ray photoelectron spectroscopy (XPS). The as-synthesized RGO/Cu NWs nanostructure is found to be almost coating structure of particle-free, high aspect ratio (L/D≈890) Cu NWs decorated with reduced graphene oxide (RGO), which accounts for the outstanding oxidation resistance. The stability tests show that the sheet resistance (RS) of the RGO/Cu NWs is almost unchanged over 20 days at room temperature or 5 h at 60 °C. What’s more, the sheet resistance of the RGO/Cu NWs with coating structure only increases to 2.48 times after being heated for 150 min at 100 °C, which can directly indicate that the RGO/Cu NWs nanostructure has excellent anti-oxidation resistance and temporal stability. Also, the as-prepared RGO/Cu NWs transparent electrode has both low sheet resistance of 58.36 Ω/sq and high optical transmittance (87.12% @550 nm). The composite materials provide a better strategy to resolve the problem of being easily oxidized for Cu NWs and promote their wide practical applications.

Pulse-Width and Temperature Effect on the Switching Behavior of an Etch-Stop-on-MgO-Barrier Spin-Orbit Torque MRAM Cell

In this letter, we present a novel step spin-orbit torque magnetic random access memory (SOT-MRAM) cell structure and its switching behavior. A special stop-on-MgO etch etches away the hard mask and the pinned layer while retaining the free layer (FL) and MgO as part of the cell. The extended Ta/CoFeB/MgO layer is proved to be more tolerant to the etching non-uniformity of the Ta nanowire and improve etching yield. Although etching stops on MgO, the FL underneath the thin MgO has been rendered non-magnetic by the etching process. Recessed Cu pads were added to the Ta nanowire, which substantially reduces the overall resistance of the Ta nanowire. The general switching behavior of the step SOT-MRAM cells, such as pulse-width and temperature dependence of the switching currents, resembles that of a spin-transfer torque MRAM cell.

Oxidation and erosion resistance of multi-layer SiC nanowires reinforced SiC coating prepared by CVD on C/C composites in static and aerodynamic oxidation environments

A multi-layer SiC nanowires reinforced SiC (SiCnws-SiC) coating was prepared in-situ on carbon/carbon (C/C) composites by three chemical vapor deposition (CVD) processes. The microstructure and phase composition of the nanowires fabricated on the first-layer SiCnws-SiC coating and the coatings were examined by SEM, TEM, and XRD. The bamboo-like SiC nanowires with a 50 nm diameter and a length of several tens of micrometers are straight, randomly orientated and distributed like a net on the first-layer SiCnws-SiC coating. The growth direction is [111], and the growth mechanism is VS. The multi-layer SiCnws-SiC coating has three layers: the thickness of the first-layer is roughly 400 µm, and the outer two layers are about 200 µm. Each layer has a sandwich structure. The isothermal oxidation and erosion resistance of the multi-layer SiCnws-SiC coating were investigated in an electrical furnace and a high temperature wind tunnel. The results indicated that the weight loss of the multi-layer SiCnws-SiC coated C/C composites was only 1.8% after oxidation in static air at 1773 K for 361 h. Further, the coated sample failed due to fracture of the coating at the clamping position (i.e. 80 mm) after erosion at 1873 K for 130 h in the wind tunnel. The weight loss of the coated C/C composites occurred due to the formation of penetrating cracks in the coating during the oxidation thermal shock. The maximum bending moment and the larger clamping force caused the coating fracture and resulted in intense oxidation of the substrate and the failure of the specimen.

Oxidation resistance of SiC nanowires reinforced SiC coating prepared by a CVD process on SiC‐coated C/C composites

AbstractOxidation protective SiC nanowires‐reinforced SiC (SiCNWs‐SiC) coating was prepared on pack cementation (PC) SiC‐coated carbon/carbon (C/C) composites by a simple chemical vapor deposition (CVD) process. This double‐layer SiCNWs‐SiC/PC SiC‐coating system on C/C composites not only has the advantages of SiC buffer layer but also has the toughening effects of SiCNWs. The microstructure and phase composition of the nanowires and the coatings were examined by SEM, TEM, and XRD. The single‐crystalline β‐SiC nanowires with twins and stacking faults were deposited uniformly and oriented randomly with diameter of 50‐200 nm and length ranging from several to tens micrometers. The dense SiCNWs‐SiC coating with some closed pores was obtained by SiC nanocrystals stacked tightly with each other on the surface of SiCNWs. After introducing SiCNWs in the coating system, the oxidation resistance is effectively improved. The oxidation test results showed that the weight loss of the SiCNWs‐SiC/PC SiC‐coated samples was 4.91% and 1.61% after oxidation at 1073 K for 8 hours and at 1473 K for 276 hours, respectively. No matter oxidation at which temperature, the SiCNWs‐SiC/PC SiC‐coating system has better anti‐oxidation property than the single‐layer PC SiC coating or the double‐layer CVD SiC/PC SiC coating without SiCNWs.

Diagnosis of phosphorus monolayer doping in silicon based on nanowire electrical characterisation

The advent of high surface-to-volume ratio devices has necessitated a revised approach to parameter extraction and process evaluation in field-effect transistor technologies. In this work, active doping concentrations are extracted from the electrical analysis of Si nanowire devices with high surface-to-volume ratios. Nanowire resistance and Si resistivity are extracted, by first extracting and subtracting out the contact resistance. Resistivity (ρ) is selected as the benchmark parameter to compare different doping processes with each other. The impacts of nanowire diameter scaling to 10 nm and of nanowire spacing scaling to <20 nm are extracted for monolayer doping and beam-line ion implantation. Despite introducing significant crystal damage, P beam-line ion implantation beats allyldiphenylphosphine (ADP) P monolayer doping with a SiO2 cap in terms of lower Si resistivity and higher dopant activation, with dependencies on the nanowire width greater than on nanowire spacing. Limitations in ADP P monolayer doping with a SiO2 cap are due to the difficulties in dopant incorporation, as it is based on in-diffusion, and P atoms must overcome a potential barrier on the Si surface.

In situ study on surface roughening in radiation-resistant Ag nanowires

Metallic materials subjected to heavy ion irradiation experience significant radiation damage. Free surface is a type of effective defect sinks to improve the radiation resistance in metallic materials. However, the radiation resistance of metallic nanowires (NWs) is largely unknown. Here we show, via in situ Kr ion irradiations in a transmission electron microscope, Ag NWs exhibited much better radiation resistance than coarse-grained Ag. Irradiation-induced prominent surface roughening in Ag NWs provides direct evidence for interaction between defect clusters and free surface. Diameter dependent variation of the surface roughness in irradiated Ag NWs has also been observed. This study provides insight on mechanisms of enhanced radiation resistance via free surfaces in metallic NWs.

Vertically Stacked Cantilever n-Type Poly-Si Junctionless Nanowire Transistor and Its Series Resistance Limit

We had successfully suspended the vertically stacked cantilever (VSC) nanowire by two approaches: 1) inserting a SiN layer as reinforcement to sustain the gate-stack thermal budget and 2) adopting high- ${k}$ metal gate low-temperature process and realizing gate-all-around structure, which shows better subthreshold characteristics. Feasibility of improving current level within the same footprint and without degrading subthreshold performance is demonstrated. Series resistance limit is pointed out as a bottle neck for current increment with respect to layers of channels. Further investigation of reducing the series resistance of VSC nanowire is needed for any future circuit integration.

Electrical and thermal properties of silver nanowire fabricated on a flexible substrate by two-beam laser direct writing for designing a thermometer

Accurate knowledge of electrical conductivity and thermal conductivity temperature dependence plays a crucial role in the design of a thermometer. Here, by using a two-beam laser direct writing system, an individual silver nanowire (AgNW) with well-defined dimensions is fabricated on a polyethylene terephthalate (PET) substrate. The temperature dependence of the resistivity of the fabricated AgNW is measured ranging from 10 to 300 K, and fitted with the Bloch–Grüneisen formula. The residual resistivity ((1.62 ± 0.20) × 10−7 Ω m) of the AgNW is larger than that of the bulk material (1 × 10−11 Ω m). The electron–phonon coupling constant of the AgNW is (1.08 ± 0.13) × 10−7 Ω m, which is larger than that of the bulk silver (5.24 × 10−8 Ω m). Moreover, the Debye temperature of the AgNW is 199.30 K and is lower than that of the bulk silver (235 K). The Lorenz number of the fabricated AgNW is found to decrease as the temperature increases. Besides, the Lorenz number (2.66 × 10−7 W Ω K−2) is larger than the Sommerfeld value (2.44 × 10−8 W Ω K−2) at room temperature. The measurement results allow one to design a thermometer in the temperature range 40–300 K. The flexibility of the AgNW is also excellent, and the resistance increase of the AgNW is only 2.58% when the AgNW bending about 1000 times with a bending radius of 1 mm.

Temperature dependence of electrical properties of electrodeposited Ni-based nanowires

The influence of annealing on the microstructure and the electrical properties of cylindrical nickel-based nanowires has been investigated. Nanowires of nickel of nominally 200 nm diameter and of permalloy (Py) of nominally 70 nm were fabricated by electrochemical deposition into nanoporous templates of polycarbonate and anodic alumina, respectively. Characterization was carried out on as-grown nanowires and nanowires heat treated at 650°C. Transmission electron microscopy and diffraction imaging of as-grown and annealed nanowires showed temperature-correlated grain growth of an initially nano-crystalline structure with ≤8 nm (Ni) and ≤20 nm (Py) grains towards coarser poly-crystallinity with grain sizes up to about 160 nm (Ni) and 70 nm (Py), latter being limited by the nanowire width. The electrical conductivity of individual as-grown and annealed Ni nanowires was measured in situ within a scanning electron microscope environment. At low current densities, the conductivity of annealed nanowires was estimated to have risen by a factor of about two over as-grown nanowires. We attribute this increase, at least in part, to the observed grain growth. The annealed nanowire was subsequently subjected to increasing current densities. Above 120 kA mm-2 the nanowire resistance started to rise. At 450 kA mm-2 the nanowire melted and current flow ceased.

A Nose for Hydrogen Gas: Fast, Sensitive H2 Sensors Using Electrodeposited Nanomaterials.

Hydrogen gas (H2) is odorless and flammable at concentrations above 4% (v/v) in air. Sensors capable of detecting it rapidly at lower concentrations are needed to "sniff" for leaked H2 wherever it is used. Electrical H2 sensors are attractive because of their simplicity and low cost: Such sensors consist of a metal (usually palladium, Pd) resistor. Exposure to H2 causes a resistance increase, as Pd metal is converted into more resistive palladium hydride (PdHx). Sensors based upon Pd alloy films, developed in the early 1990s, were both too slow and too insensitive to meet the requirements of H2 safety sensing. In this Account, we describe the development of H2 sensors that are based upon electrodeposited nanomaterials. This story begins with the rise to prominence of nanowire-based sensors in 2001 and our demonstration that year of the first nanowire-based H2 sensor. The Pd nanowires used in these experiments were prepared by electrodepositing Pd at linear step-edge defects on a graphite electrode surface. In 2005, lithographically patterned nanowire electrodeposition (LPNE) provided the capability to pattern single Pd nanowires on dielectrics using electrodeposition. LPNE also provided control over the nanowire thickness (±1 nm) and width (±10-15%). Using single Pd nanowires, it was demonstrated in 2010 that smaller nanowires responded more rapidly to H2 exposure. Heating the nanowire using Joule self-heating (2010) also dramatically accelerated sensor response and recovery, leading to the conclusion that thermally activated H2 chemisorption and desorption of H2 were rate-limiting steps in sensor response to and recovery from H2 exposure. Platinum (Pt) nanowires, studied in 2012, showed an inverted resistance response to H2 exposure, that is, the resistance of Pt nanowires decreased instead of increased upon H2 exposure. H2 dissociatively chemisorbs at a Pt surface to form Pt-H, but in contrast to Pd, it stays on the Pt surface. Pt nanowires showed a faster response to H2 exposure than Pd nanowires operating at the same elevated temperature, but they had a surprising disadvantage: The resistance change observed for Pt nanowires was exactly the same for all H2 concentrations. Electron surface scattering was implicated in the mechanism for these sensors. Work on Pt nanowires lead in 2015 to the preparation of Pd nanowires that were electrochemically modified with thin Pt layers (Pd@Pt nanowires). Relative to Pd nanowires, Pt@Pd nanowires showed accelerated response and recovery to H2 while retaining the same high sensitivity to H2 concentration seen for sensors based upon pure Pd nanowires. A new chapter in H2 sensing (2017) involves the replacement of metal nanowires with carbon nanotube ropes decorated with electrodeposited Pd nanoparticles (NPs). Even higher sensitivity and faster sensor response and recovery are enabled by this sensor architecture. Sensor properties are strongly dependent on the size and size monodispersity of the Pd NPs, with smaller NPs yielding higher sensitivity and more rapid response/recovery. We hope the lessons learned from this science over 15 years will catalyze the development of sensors based upon electrodeposited nanomaterials for gases other than H2.

A silicon nanowire heater and thermometer

In the thermal conductivity measurements of thermoelectric materials, heaters and thermometers made of the same semiconducting materials under test, forming a homogeneous system, will significantly simplify fabrication and integration. In this work, we demonstrate a high-performance heater and thermometer made of single silicon nanowires (SiNWs). The SiNWs are patterned out of a silicon-on-insulator wafer by CMOS-compatible fabrication processes. The electronic properties of the nanowires are characterized by four-probe and low temperature Hall effect measurements. The I-V curves of the nanowires are linear at small voltage bias. The temperature dependence of the nanowire resistance allows the nanowire to be used as a highly sensitive thermometer. At high voltage bias, the I-V curves of the nanowire become nonlinear due to the effect of Joule heating. The temperature of the nanowire heater can be accurately monitored by the nanowire itself as a thermometer.

Dynamic response of shear thickening fluid reinforced with SiC nanowires under high strain rates

In this letter, SiC nanowires were adopted to reinforce the nanoparticle-based shear thickening fluid (STF) to improve its rheological properties. The reinforced STF showed a significant increase in viscosity. A Split-Hopkinson pressure bar was implemented to evaluate the dynamic response of STF at strain rates in the range of 3 × 103–1.2 × 104/s. For the pure STF, the flow stress reaches a saturation value with increasing strain rates and shows almost no strain rate sensitivity, whereas the flow stress of the reinforced STF increases with strain rates, and the strain rate sensitivity to flow stress is obvious owing to the resistance of nanowires. The essence of this study is to reveal that there is a limiting value of the flow stress of traditional nanoparticle-based STF at high strain rates due to the lubrication force among particles. SiC nanowires can be used to break this limitation of the nanoparticle-based STF.

A molecular dynamics simulation study of irradiation induced defects in gold nanowire

Displacement cascade in gold nanowires was studied using molecular dynamics computer simulations. Primary knock-on atoms (PKAs) with different kinetic energies were initiated either at the surface or at the center of the nanowires. We found three kinds of defects that were induced by the cascade, including point defects, stacking faults and crater at the surface. The starting points of PKAs influence the number of residual point defects, and this consequently affect the boundary of anti-radiation window which was proposed by calculation of diffusion of point defects to the free surface of nanowires. Formation of stacking faults that expanded the whole cross-section of gold nanowires was observed when the PKA’s kinetic energy was higher than 5keV. Increasing the PKA’s kinetic energy up to more than 10keV may lead to the formation of crater at the surface of nanowires due to microexplosion of hot atoms. At this energy, PKAs started from the center of nanowires can also result in the creation of crater because length of cascade region is comparable to diameter of nanowires. Both the two factors, namely initial positions of PKAs as well as the craters induced by higher energy irradiation, would influence the ability of radiation resistance of metal nanowires.

Electron beam dose dependence of surface recombination velocity and surface space charge in semiconductor nanowires

The characterization of nanowires (NWs) often requires the use of scanning electron beam techniques because of their high spatial resolution. However, the impact of the high energetic electron beam on the physical parameters under investigation is rarely taken into account. In this work, a combination of optical and electrical techniques is involved for the measurement of the electron beam dose (EBD) dependence of cathodoluminescence intensity, exciton diffusion length and electrical resistance in ZnO NWs. Large EBD dependences of these key parameters are observed and their reversibility is investigated. The results are discussed in terms of bulk and surface reversible modifications. In particular, the behaviors of surface recombination velocity and surface space charge under electron beam exposure are determined and simulated. This study points out that caution must be taken and experimental protocols must be well defined when measuring physical parameters of NWs using electron beam techniques.

Influence of magnetic properties on electric resistivity of iron-group elements

A novel effective method of distinguishing between phonon and magnetic contributions into the total resistivity of 3d metals is presented. The method allows for the nonlinear character of interatomic forces and their change with temperature. Obtained results are important for quantitative estimates of the magnetic properties of ferromagnetic materials, including the nanostructured. This is illustrated by a calculation of the temperature behavior of s–d exchange interaction energy in 3d metals and by description of the temperature dependence of the resistivity of a one-threaded ferromagnetic nanowire made of Ni.

3D Nanoprinting via laser-assisted electron beam induced deposition: growth kinetics, enhanced purity, and electrical resistivity.

We investigate the growth, purity, grain structure/morphology, and electrical resistivity of 3D platinum nanowires synthesized via electron beam induced deposition with and without an in situ pulsed laser assist process which photothermally couples to the growing Pt–C deposits. Notably, we demonstrate: 1) higher platinum concentration and a coalescence of the otherwise Pt–C nanogranular material, 2) a slight enhancement in the deposit resolution and 3) a 100-fold improvement in the conductivity of suspended nanowires grown with the in situ photothermal assist process, while retaining a high degree of shape fidelity.

Investigation of factors affecting electrical contacts on single germanium nanowires

We report an experimental investigation of the quality of electrical contacts made on single Germanium nanowires (grown using Au catalyst from vapor) using Cr/Au contact pads. The nanowires are single crystalline and have a thin layer of oxide on them. We find that a low specific contact resistivity of 10−6 Ω cm2 can be obtained in nanowires with low resistance and the contact resistance enhances almost linearly with the nanowire resistivity. The metal semiconductor junction shows an ideality factor close to unity. A low barrier height of 0.15 eV can be obtained in nanowires of lower resistivities which increase to nearly 0.3 eV for nanowires of higher resistivity. The experiments were carried down to 10 K, and junction characteristics as a function of temperature were evaluated. The specific contact resistance increases on cooling but the barrier shows suppression as the nanowire is cooled, along with an enhancement of the ideality factor. We analyze the temperature dependence of these parameters using a model that assumes a Gaussian distribution of barrier heights in the contact region. The temperature dependence predicted by the model was observed, and the relevant parameters were obtained from the data.

Theoretical modeling of electrical resistivity and Seebeck coefficient of bismuth nanowires by considering carrier mean free path limitation

In this study, the electrical resistivity and Seebeck coefficient of bismuth nanowires, several hundred nanometers in diameter, are calculated using the Boltzmann equation in the relaxation time approximation. The three-dimensional density of states and properties of single-crystalline bulk bismuth, such as carrier density, effective mass, and mobility, are used in the calculation without considering the quantum size effect. The relaxation times of the electrons and holes are calculated using Matthiessen's rule considering the carrier collisions at the wire boundary. The temperature, crystal orientation, and diameter dependence of the electrical resistivity and Seebeck coefficient are investigated. The calculation demonstrates that the electrical resistivity increases gradually with decreasing wire diameter, and the temperature coefficient of the electrical resistivity varies from positive to negative at low temperatures for thin wires with diameters less than approximately 500 nm. The diameter dependence of the electrical resistivity varies with the crystal orientation; the increase along the bisectrix axis is larger than that along the binary and trigonal axes. The temperature dependence of the Seebeck coefficient also strongly depends on the crystal orientation. The absolute value of the negative Seebeck coefficient along the bisectrix axis rapidly decreases with decreasing diameter and even changes sign from negative to positive at low temperatures despite the charge neutrality condition, while the Seebeck coefficients along the binary and trigonal axes do not differ significantly from those of single-crystalline bulk bismuth. We conclude that the thermoelectric properties of bismuth nanowires strongly depend not only on the wire diameter but also on the crystal orientation.

Doping top-down e-beam fabricated germanium nanowires using molecular monolayers

This paper describes molecular layer doping of Ge nanowires. Molecules containing dopant atoms are chemically bound to a germanium surface. Subsequent annealing enables the dopant atoms from the surface bound molecules to diffuse into the underlying substrate. Electrical and material characterization was carried out, including an assessment of the Ge surface, carrier concentrations and crystal quality. Significantly, the intrinsic resistance of Ge nanowires with widths down to 30nm, doped using MLD, was found to decrease by several orders of magnitude.

Variability and self-average of impurity-limited resistance in quasi-one dimensional nanowires

The impurity-limited resistance in quasi-one dimensional (quasi-1D) nanowires is studied under the framework of the Lippmann–Schwinger scattering theory. The resistance of cylindrical nanowires is calculated theoretically under various spatial configurations of localized impurities with a simplified short-range scattering potential. Then, the relationship between the phase interference and the variability in the impurity-limited resistances is clarified. We show that there are two different and independent mechanisms leading to the variability in impurity-limited resistances; incoherent and phase-coherent randomization processes. The latter is closely related to the so-called “self-average” and its physical origin under nanowire structures is clarified. We point out that the ensemble average also comes into play in the cases of long channel nanowires, which leads to the self-average resistance of multiple impurities.