Conductivity Of Nanowires Research Articles

Quantized Seebeck coefficient of quasi-ballistic gold nanowires

The behavior of the Seebeck coefficient in the intermediate regime between atomic scale ballistic conduction and bulk-like diffusive conduction remains unclear. To address this, we have developed a microscale device capable of simultaneously measuring the Seebeck coefficient and electrical conductance of gold nanowires in an adiabatic environment. The nanowires were made in situ by electromigration from lithographically prepared bow-tie electrodes, yielding a wide range of wire thicknesses down to a few hundred atoms. We observed quantization of the Seebeck coefficient, a phenomenon previously observed only at the Ångstrom scale, in relatively thick wires with a thickness of several tens of nanometers. The quantized Seebeck coefficient was proportional to the reciprocal of the electrical conductance with a slope of −47.8 μV/K, indicating that electrons are spatially confined due to the electronic shell structure of the nanowire, similar to the quantization of electrical conductance.

Tuning the thermal conductivity of silicon nanowires by surface passivation

Tuning the thermal conductivity of silicon nanowires by surface passivation

Numerical modelling of interspecies electron transfer in anaerobic digestion using multiple electron donors for methane production

Direct interspecies electron transfer (DIET) is an efficient approach to enhance methane production in syntrophic metabolism during anaerobic digestion; yet a quantitative understanding of DIET mechanisms between exoelectrogens and electrotrophic methanogens is still lacking. This study presents a novel diffusion–reaction multi-physics model to simulate interspecies electron transfer between rod-shaped exoelectrogens and spherical electrotrophic methanogens for the first time. The numerical results indicate that the electron transfer rate in DIET are 5.6 to 8.8 times higher than that in interspecies hydrogen transfer (IHT). The increase of substrate concentration (0.001 − 0.1 mol/L), nanowire conductivity (0.1 − 50 Ω⋅m), nanowire number (1 − 1.0 × 104) and redox cofactor number (10 − 1.0 × 104) significantly enhance electron transfer of DIET in syntrophic metabolism. Furthermore, the presence of conductive material can increase the electron transfer rates of DIET by up to 56.6–85.1 times compared to the control group. This study provides new insights into the optimization of DIET in the anaerobic digestion of organic wastes, offering a quantitative basis for improving methane production through targeted manipulation of system parameters.

Geometric Variability‐Aware Thermal Characteristics Modeling of Nanoscale Silicon Gate‐All‐around Nanowire Transistor

Thermal management becomes increasingly important in silicon gate‐all‐around (GAA) field‐effect transistor (FETs) for 3 nm technology node and beyond. The channel thermal conductivity significantly differs from bulk silicon. Precise determination of thermal conductivity is crucial for device evaluation and optimization. This study investigates the thermal conductivity of silicon nanowires, examining the complex interplay between size and channel orientation. The conventional nonequilibrium molecular dynamics (NEMD) method is used with the standard Stillinger–Weber potential at the atomic scale. The results indicate that the thermal conductivity of silicon nanowires along the [100] direction increases monotonically with both length (L) and cross‐sectional side length (D). Conversely, the [110] direction exhibits nonmonotonic variation in thermal conductivity with D, due to increased acoustic–optic phonon scattering. For GAA FET devices with a silicon nanowire channel of L = 20 nm and D = 5 nm, the NEMD calculations yield thermal conductivities of 10.8 W m·K−1 for the [100] direction and 25.3 W m·K−1 for the [110] direction. Subsequently, the self‐heating effect (SHE) in silicon nanowire GAA FETs by technology computer‐aided design with the modified channel conductivity is analyzed. The results suggest that silicon nanowires with the [110] transport direction are more suitable for device design.

Atomistic wave packet investigation of phonon scattering at rough surfaces

Investigating the phonon-surface scattering mechanism is essential for the evaluation of thermal transport in nanostructures. The theoretical description to quantify this mechanism remains to be developed at the atomic scale. This work presents a phonon wave packet method to study the phonon-surface scattering behavior at rough surfaces. We obtain the specularity distribution dependent on phonon polarization, wavelength, and surface roughness. The reflection of the diffuse wave packet is primarily attributed to the surface shadowing effect at a higher incident angle, surface disorder, and surface-induced localized modes. Taking the wavevector-dependent specularity data as input, the thermal conductivity of silicon nanowires is calculated based on the Boltzmann Transport Equation. Our specularity model provides an accurate evaluation for predicting thermal conductivity. This work offers an atomic-level analysis for phonon-surface interaction, which is helpful for the understanding of thermal transport in nanostructures.

Synthesis and morphology of Ag nanowires by fiber template method

The synthesis of traditional silver nanowires often uses a polyol method. There are many factors that affect the structure of silver nanowires, such as silver ion concentration, type and amount of reducing agent, oxygen concentration, stirring speed, temperature, and time. The synthesis conditions are harsh and difficult to replicate. In this paper, natural fibers and synthetic fibers were used as templates to assist the polyol reduction method to obtain silver nanowires with uniform structure. The effect of fiber types on the structure of silver nanowires were studied, including hemp fibers, wheat straw fibers, tobacco stem fibers, and polycarbonate fibers. Polycarbonate fibers induced the synthesis of silver nanowires with the highest aspect ratio, highest yield, and most uniform diameter distribution. The effect of polycarbonate fibers concentrations on the morphology and conductivity of silver nanowires were also studied. When the polycarbonate mass concentration was 8.5 × 10−4 g/mL, the aspect ratio of silver nanowires was the highest. The effect of polycarbonate fibers length (2 mm\\5 mm\\7 mm) on the morphology of silver nanowires were also studied. When the length of the template polycarbonate fibers was 7 mm, the length to diameter ratio and conductivity of the nanowires obtained are the best. Furthermore, the reaction kinetics of the reaction were studied via multiple sampling of silver nanowire reaction solutions and characterized by using UV–visible spectroscopy and scanning electron microscopy. The synthesis method of silver nanowires using fiber template is simple and fast, and can be used to synthesize silver nanowires with uniform diameter distribution on a large scale, thus solving the bottleneck problem of harsh synthesis conditions for silver nanowires. The resulting silver nanowires were blended with carboxymethyl cellulose to prepare conductive inks, which were coated on paper and cured at 180 °C for 30 min to achieve good conductivity.

A novel flexible magnetoelastic biosensor with “sandwich” structure based on transferrin encapsulated gold nanoclusters for 5-hydroxytryptamine detection

5-hydroxytryptamine (5-HT), a mono-amine neurotransmitter, plays an important role in regulating the dynamics of neural circuits in the central nervous system and enteric nervous system. Accurate and sensitive monitoring of 5-HT will provide critical information for diagnosing many psychiatric and neurological disorders. However, there are no superior clinical assays for the detection of 5-HT, and existing methods of gas chromatographs and mass spectrometers are expensive, limiting portable and real-time monitoring as diagnostic approaches in the clinical setting. Therefore, a convenient, rapid, and low-cost method for the detection of 5-HT is still in demand in current clinical medicine. Herein, a novel flexible magnetoelastic (ME) biosensor with “sandwich” structure is proposed for 5-HT detection based on transferrin encapsulated gold nanoclusters (Tf-AuNCs). Combined with the magnetoelastic effect of CoFe2O4, the excellent conductivity of silver nanowires (AgNWs), and the fluorescence properties of Tf-AuNCs, the ME biosensor designed in this paper can achieve multi-signal recognition. Rapid and sensitive detection of 5-HT is achieved by a biosensing process that converts surface stress signal into magnetoelectric signals. The biosensor is capable of detecting 5-HT with different concentrations in a linear range of 10 ng/mL-100 μg/mL (R2 = 0.97119) with a lower detection limit (LOD) of 0.33 ng/mL. The accurate measurement results of 5-HT in human serum of clinical samples demonstrated the feasibility of the biosensor for 5-HT detection. This flexible ME biosensor was prepared in a simple process with great specificity and stability, providing a portable analytical device for the rapid and sensitive detection of 5-HT, which is of great significance for the clinical research of various neurological diseases.

Investigation of the thermal conductivity of shape-modulated silicon nanowires by the Monte Carlo method combined with Green–Kubo formalism

Investigation of the thermal conductivity of shape-modulated silicon nanowires by the Monte Carlo method combined with Green–Kubo formalism

Non-enzymatic SnO2-nanowire/GCE amperometric sensor for H2O2 sensing

In this paper, SnO2-nanowire was synthesized and constructed as non enzymatic sensor to detect hydrogen peroxide (H2O2). In 0.1 M PBS, the prepared SnO2-nanowire/GCE amperometric sensor exhibits a well performance against H2O2, with the linear detection range of 1.4 μM ∼ 6.66 mM and detection limit of 0.34 μ M. This superior electrochemical sensing performance is mainly due to the mesoporous structure, large specific surface area, and high conductivity of the SnO2 nanowire. Theoretical calculations indicate that the adsorption capacity of SnO2 (110) crystal surface for H2O2 is superior to that of SnO2 (101) crystal surface. In addition, the sensor can detect hydrogen peroxide in tap water and orange juice, showing its potential applications.

Anisotropy of the conductivity of silicon nanowires

ABSTRACT This study reports the findings from an investigation into charge carrier transport within a silicon nanowire layer. The samples were prepared using the metal-assisted chemical etching method applied to crystalline silicon wafers with a resistance of 10–20 Ω·cm. The resulting silicon nanowires had a diameter of about 100 nm with a resistance of approximately 15 kΩ·cm. Electrical conductivity measurements were performed in both planar and sandwich configurations, revealing analogous conductivity mechanisms across different geometries. Frequency-dependent conductivity studies unveiled the presence of hopping conductivity. A hypothesis is proposed regarding the existence of a potential barrier at the interface between the nanowire layer and the substrate.

Highly-doped MBE-grown GaP nanowires: Synthesis, electrical study and modeling

Efficient doping of semiconductor nanowires remains a major challenge towards the commercialization of nanowire-based devices. In this work we investigate the growth regimes and electrical properties of MBE-grown p- and n-type gallium phosphide nanowires doped with Be and Si, respectively. Electrical conductivity of individual nanowires is quantitatively studied via atomic force microscopy supported with numerical analysis. Based on conductivity measurements, we provide growth strategies for achieving the doping level up to ND=5⋅1018 cm-3 and NA=2⋅1019 cm-3 for GaP:Si and GaP:Be nanowires respectively, which is high enough for technological applications.

Rational design of MoS2@M (M=Sn, Cu, Ni, Co) hybrid nanostructures for enhanced electrocatalytic hydrogen evolution reaction

MoS2 has attracted attraction in electrocatalytic hydrogen evolution reaction (HER). The low electrical conductivity and limited exposure of active sites hindered the electrocatalytic efficiency of MoS2. In this paper, we design MoS2@M (M = Sn, Cu, Ni, Co) hybrid nanostructures by growing MoS2 nanosheets on the surface of M (M = Sn, Cu, Ni, Co) nanowires. Due to the high conductivity of metal nanowires and the increased HER active sites, the MoS2@M (M = Sn, Cu, Ni, Co) hybrid nanostructures show a superior HER efficiency. In alkaline media, the MoS2@M (M = Sn, Cu, Ni, Co) hybrid nanostructures exhibit the low overpotential of 130–172 mV at the current density of 10 mA/cm2 and a small Tafel slope of 61–86 mV/dec. In addition, the MoS2@M (M = Sn, Cu, Ni, Co) hybrid nanostructures also possess excellent electrocatalytic durability. This work provides an efficient way to achieve highly efficient MoS2 based electrocatalysts for water splitting.

Effects of different atomic passivation on conductive and dielectric properties of silicon carbide nanowires

Based on the transport and polarization relaxation theories, the effects of hydrogen, fluorine, and chlorine atom passivation on the conductivity and dielectric properties of silicon carbide nanowires (SiCNWs) were numerically simulated. The results show that passivation can decrease the dark conductivity of SiCNWs and increase its ultraviolet photoconductivity. Among them, the photoconductivity of univalent (H) passivated SiCNWs is better than that of seven-valent (Cl, F) passivated SiCNWs. In terms of dielectric properties, the passivated SiCNWs exhibit a strong dielectric response in both deep ultraviolet and microwave regions. Hydrogen passivation SiCNWs produce the strongest dielectric response in deep ultraviolet, while fluorine passivation SiCNWs produce the strongest dielectric relaxation in the microwave band, which indicates that atomic passivation SiCNWs have a wide range of applications in ultraviolet optoelectronic devices and microwave absorption and shielding.

Quasi-ballistic thermal transport in silicon carbide nanowires

Silicon carbide (SiC) is an important industrial material that enables the thermal stability of power electronics. However, the nanoscale phenomenon of ballistic thermal conduction, which may further improve the thermal performance, remains unexplored in SiC. Here, we reveal the length and temperature scales at which SiC exhibits quasi-ballistic thermal conduction. Our time-domain thermoreflectance measurements probe the thermal conductivity of SiC nanowires as a function of their length and temperature. The deviation of the thermal conductivity from the diffusive limit in nanowires shorter than a few micrometers indicates the transition into a quasi-ballistic thermal conduction regime. Naturally, the deviation is greater at lower temperatures, yet the effect persists even above room temperature. Our Monte Carlo simulations of phonon transport support our experimental results and show how phonons with long mean free paths carry a substantial amount of heat, causing quasi-ballistic conduction. These findings show that quasi-ballistic heat conduction can persist at the microscale at operating temperatures of power devices, and thus may help improve the thermal design in electronics based on SiC.

TEM-compatible microdevice for the complete thermoelectric characterization of epitaxially integrated Si-based nanowires.

Nanostructured materials present improved thermoelectric properties due to non-trivial effects at the nanoscale. However, the characterization of individual nanostructures, especially from the thermal point of view, is still an unsolved topic. This work presents the complete structural, morphological, and thermoelectrical evaluation of the selfsame individual bottom-up integrated nanowire employing an innovative micro-machined device compatible with transmission electron microscopy whose fabrication is also discussed. Thanks to a design that arranges the nanostructured samples completely suspended, detailed structural analysis using transmission electron microscopy is enabled. In the same device architecture, electrical collectors and isolated heaters are available at both ends of the trenches for thermoelectrical measurements of the nanowire i.e. thermal and electrical properties simultaneously. This allows the direct measurement of the nanowire power factor. Furthermore, micro-Raman thermometry measurements were performed to evaluate the thermal conductivity of the same suspended silicon nanowire. A thermal profile of the self-heating nanowire could be spatially resolved and used to compute the thermal conductivity. In this work, heavily-doped silicon nanowires were grown on this microdevices yielding a thermal conductivity of 30.8 ± 1.7 W Km-1 and a power factor of 2.8 mW mK-2 at an average nanowire temperature of 400 K. Notably, no thermal contact resistance was observed between the nanowire and the bulk, confirming the epitaxial attachment. The device presented here shows remarkable utility in the challenging thermoelectrical characterization of integrated nanostructures and in the development of multiple devices such as thermoelectric generators.

Pressure Impact on Lattice Thermal Conductivity and Its Related Parameters in CdSe Bulk, Nanowires, and Thin Film

The hydrostatic pressure effect on lattice thermal conductivity (LTC) in CdSe bulk, nanowires, and thin films was calculated. Values of LTC obtained through Callaway with that of Clapeyron equations are used to correlate those of the experimentally measured curves. Frequency‐dependent relaxation time approximation of phonon‐scattering processes was considered, which scattering due to boundary, imperfections, dislocations, electron, and other phonons via Umklapp and normal processes were used and clarified their effects. The impact of pressure on LTC is clarified according to both sample boundary dislocation concentrations. The influence of pressure is described, along with how the size dependence of the melting temperature, Debye temperature, and phonon group velocity of CdSe nanocrystals is affected. These parameters decrease as pressure increases.

High-Transconductance and Low-Leakage Current Single Aluminum Nitride Nanowire Field Effect Transistor

This study presents electrical transport properties of a catalyst-free grown single aluminum nitride nanowire field effect transistor (AlNNW-FET) exhibiting a very high transconductance of 26.9 pS, high on/off current ratio of 795.9, high conductivity of 9.8 x 10-4 Ω-1.cm-1, and a very low leakage current of 10 pA. The conductivity of AlN nanowire is two orders of magnitude higher than the reported studies. The AlNNW-FET reveals a dominant p-type conductivity. The p-type conductivity can be attributed to aluminum vacancies and complexes composed of Al vacancies and oxygen impurities. In consequence, the fabricated AlNNW-FET with high-performance, cost-effectiveness, and high-power efficiency is very well suited for use in low power and high temperature nanoelectronic and piezoelectric sensor applications, as well as integrated electro-optical devices including optomechanical devices and pyroelectric photodetectors.

Diameter-dependent ultra-high thermoelectric performance of ZnO nanowires

Zinc oxide (ZnO) shows great potential in electronics, but its large intrinsic thermal conductivity limits its thermoelectric applications. In this work, we explore the significant carrier transport capacity and diameter-dependent thermoelectric characteristics of wurtzite-ZnO 〈0001〉 nanowires based on first-principles and molecular dynamics simulations. Under the synergistic effect of band degeneracy and weak phonon–electron scattering, P-type (ZnO)73 nanowires achieve an ultra-high power factor above 1500 μW⋅cm−1⋅K−2 over a wide temperature range. The lattice thermal conductivity and carrier transport properties of ZnO nanowires exhibit a strong diameter size dependence. When the ZnO nanowire diameter exceeds 12.72 Å, the carrier transport properties increase significantly, while the thermal conductivity shows a slight increase with the diameter size, resulting in a ZT value of up to 6.4 at 700 K for P-type (ZnO)73. For the first time, the size effect is also illustrated by introducing two geometrical configurations of the ZnO nanowires. This work theoretically depicts the size optimization strategy for the thermoelectric conversion of ZnO nanowires.

Solvent Welding-Based Methods Gently and Effectively Enhance the Conductivity of a Silver Nanowire Network

To enhance the conductivity of a silver nanowire (Ag NW) network, a facile solvent welding method was developed. Soaking a Ag NW network in ethylene glycol (EG) or alcohol for less than 15 min decreased the resistance about 70%. Further combined solvent processing via a plasmonic welding approach decreased the resistance about 85%. This was achieved by simply exposing the EG-soaked Ag NW network to a low-power blue light (60 mW/cm2). Research results suggest that poly(vinylpyrrolidone) (PVP) dissolution by solvent brings nanowires into closer contact, and this reduced gap distance between nanowires enhances the plasmonic welding effect, hence further decreasing resistance. Aside from this dual combination of methods, a triple combination with Joule heating welding induced by applying a current to the Ag NW network decreased the resistance about 96%. Although conductivity was significantly enhanced, our results showed that the melting at Ag NW junctions was relatively negligible, which indicates that the enhancement in conductivity could be attributed to the removal of PVP layers. Moreover, the approaches were quite gentle so any potential damage to Ag NWs or polymer substrates by overheating (e.g., excessive Joule heating) was avoided entirely, making the approaches suitable for application in devices using heat-sensitive materials.

Electrical and Thermal Conductivities of Single CuxO Nanowires.

Copper oxide nanowires (NWs) are promising elements for the realization of a wide range of devices for low-power electronics, gas sensors, and energy storage applications, due to their high aspect ratio, low environmental impact, and cost-effective manufacturing. Here, we report on the electrical and thermal properties of copper oxide NWs synthetized through thermal growth directly on copper foil. Structural characterization revealed that the growth process resulted in the formation of vertically aligned NWs on the Cu growth substrate, while the investigation of chemical composition revealed that the NWs were composed of CuO rather than Cu2O. The electrical characterization of single-NW-based devices, in which single NWs were contacted by Cu electrodes, revealed that the NWs were characterized by a conductivity of 7.6 × 10-2 S∙cm-1. The effect of the metal-insulator interface at the NW-electrode contact was analyzed by comparing characterizations in two-terminal and four-terminal configurations. The effective thermal conductivity of single CuO NWs placed on a substrate was measured using Scanning Thermal Microscopy (SThM), providing a value of 2.6 W∙m-1∙K-1, and using a simple Finite Difference model, an estimate for the thermal conductivity of the nanowire itself was obtained as 3.1 W∙m-1∙K-1. By shedding new light on the electrical and thermal properties of single CuO NWs, these results can be exploited for the rational design of a wide range of optoelectronic devices based on NWs.