Conductivity Of Nanowires Research Articles

Electrical characterization of an individual nanowire using flexible nanoprobes fabricated by atomic force microscopy-based manipulation

Nanowires have emerged as promising one-dimensional materials with which to construct various nanocircuits and nanosensors. However, measuring the electrical properties of individual nanowires directly remains challenging because of their small size, thereby hindering the comprehensive understanding of nanowire-based device performance. A crucial factor in achieving reliable electrical characterization is establishing well-determined contact conditions between the nanowire sample and the electrodes, which becomes particularly difficult for soft nanowires. Introduced here is a novel technique for measuring the conductivity of an individual nanowire with the aid of automated nanomanipulation using an atomic force microscope. In this method, two nanowire segments cut from the same silver nanowire are positioned onto a pair of gold electrodes, serving as flexible nanoprobes to establish controllable contact with the sample. By changing the contact points along the nanowire sample, conductivity measurements can be performed on different regions, thereby eliminating the influence of contact resistance by analyzing multiple current–voltage curves. Using this approach, the resistivity of a 100-nm-diameter silver nanowire is determined to be 3.49 × 10−8 Ω m.

First principles study on the thermoelectric properties of GaN nanowires with CN point defects

In this paper, the effects of CN point defects on the thermoelectric properties of GaN nanowires (NWs) were investigated by using first principles calculation. It is found that the CN point defects can increase the electronic density of states (DOS) near the Fermi level of GaN NWs. The calculation results indicate that CN point defects are beneficial for improving the power factor (PF) of GaN NWs. In addition, it was found that CN point defects can increase the electrical conductivity of NWs. At the same time, it also has impact on the thermal conductivity and Seebeck coefficient of NWs. CN point defects will increase the electrical conductivity of GaN NWs from 0.41 × 10 14Wm−1k−1s−1 to 1.15 × 10 14Wm−1k−1s−1 at T = 700 K. In addition, it's also found that as the temperature increases, CN will cause the Seebeck coefficient decreased from 0.001 VK−1 to 0.0008 VK−1 when T = 700 K. It’s useful for further understanding the thermoelectric properties of wide bandgap semiconductor materials and improving the performance of thermoelectric devices.

Size and kink effects on thermal conductivity in nickel nanowires

The potential applications of nanowires in thermal management and thermoelectric energy conversion have sparked extensive research on thermal transport in various nanowires. Nickel nanowires, with their unique properties and promising applications, have been extensively studied. However, the influence of size, particularly the impact of kink structures, on the thermal transport behavior in nickel nanowires remains unclear. In this paper, we employed electron-beam lithography and liftoff techniques to fabricate suspended nickel nanowires with varying sizes and kinks to experimentally investigate the size and kink effect on the thermal conductivity. The experimental results revealed that the thermal transport behavior of nickel nanowires is significantly influenced by both size and kink effects. Notably, as the nanowire size decreases, the thermal conductivity also decreases. Furthermore, we discovered that the thermal conductivity can be adjusted by altering the number and angle of kinks. Increasing the number of kinks from 18 to 36 resulted in a significant decrease in thermal conductivity. In contrast, as the kink angle decreased from 157° to 90°, the thermal conductivity also decreased. However, intriguingly, when the kink angle was further decreased from 90° to 43°, the thermal conductivity increases. This non-monotonic change in thermal conductivity with the kink angle provides an interesting insight into the intricate behavior of heat carriers in kinked nickel nanowires. Additionally, we found that varying the alloy elements can profoundly alter the thermal conductivity of nanowires with kinks. These results offer valuable insights into the behaviors of heat carriers, including electrons and phonons, during heat transfer in nickel nanowires.

Remarkable Thermal Conductivity Reduction of Silicon Nanowires during the Bending Process.

The one-dimensional geometry of silicon nanowire helps to overcome the rigid and brittle nature of bulk silicon and enables it to withstand substantial bending stresses. This provides exciting opportunities for the development of flexible electronics. The bending strain introduces atomic displacement in the lattice structure, which inherently has a significant impact on the thermal conductivity. The strain-dependent thermal conductivity of silicon nanowire is crucial to the thermal management and performance of flexible electronic devices. However, in situ thermal conductivity measurement of bending silicon nanowires remains challenging and unreported due to the varying thermal contact resistances between the sample and sensor/heat sink. In this study, the Raman spectroscopy-assisted steady state thermal conductivity measurement method is coupled with a micromanipulation system to successively monitor the thermal conductivity variation of silicon nanowires during the bending process. The result shows that the thermal conductivity of silicon nanowires steeply decreases 55-78% owing to the strain-induced structural deformation during bending. Furthermore, the proposed in situ thermal conductivity measurement method can also be extended to other nanomaterials.

Length dependent thermal conductivity of silicon and copper nanowire: a molecular dynamics study

The miniaturization and higher power density of modern electronics pose a significant challenge in thermal management. A key focus in addressing this challenge revolves around the advancement of thermal interfaces within microchip packaging, aiming to enhance thermal energy dissipation and optimization of performance. Copper nanowires are extensively employed in the chip industry as interconnects for signal transmission and thermal management purposes. Investigating the impact of reduced cross-section on the thermal transport properties of nanowires is crucial. In this study, the thermal conductivity of copper and silicon nanowires is studied with variations in the length of the nanowires. The simulation is conducted with the Equilibrium Molecular Dynamics (EMD) process. The cross-section of the nanowire is kept fixed (10 × 10 nm) and with the increase in length, its thermal conductivity is studied. At room temperature for a 50 nm length, the lattice thermal conductivity value is 1.68 and 0.037 W m − 1 K − 1 for silicon and copper nanowires, respectively. We further studied the phonon scattering, mean free path, and group velocity of silicon and copper lattices. Our study may help to design more thermally efficient microchips and innovate new cooling methods of microelectronics.

Thermal Conductivity of 3C/4H-SiC Nanowires by Molecular Dynamics Simulation.

Silicon carbide (SiC) is a promising material for thermoelectric power generation. The characterization of thermal transport properties is essential to understanding their applications in thermoelectric devices. The existence of stacking faults, which originate from the "wrong" stacking sequences of Si-C bilayers, is a general feature of SiC. However, the effects of stacking faults on the thermal properties of SiC are not well understood. In this study, we evaluated the accuracy of Tersoff, MEAM, and GW potentials in describing the thermal transport of SiC. Additionally, the thermal conductivity of 3C/4H-SiC nanowires was investigated using non-equilibrium molecular dynamics simulations (NEMD). Our results show that thermal conductivity exhibits an increase and then saturation as the total lengths of the 3C/4H-SiC nanowires vary from 23.9 nm to 95.6 nm, showing the size effect of molecular dynamics simulations of the thermal conductivity. There is a minimum thermal conductivity, as a function of uniform period length, of the 3C/4H-SiC nanowires. However, the thermal conductivities of nanowires weakly depend on the gradient period lengths and the ratio of 3C/4H. Additionally, the thermal conductivity of 3C/4H-SiC nanowires decreases continuously from compressive strain to tensile strain. The reduction in thermal conductivity suggests that 3C/4H-SiC nanowires have potential applications in advanced thermoelectric devices. Our study provides insights into the thermal transport properties of SiC nanowires and can guide the development of SiC-based thermoelectric materials.

Structural, Photophysical, and Transport Properties of Porous MAPbBr3 Single Nanowire and Nanodevice for Electrochemical Sensing

In this paper, we report synthesis of porous methylammonium lead tribromide (MAPbBr3) nanowires via self-template-directed method with dimensions of 13 ± 3 μm in length and 700 ± 100 nm in width. The perovskite single nanowires with correct compositions are demonstrated uniform in crystallinity and high in porosity by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The current-voltage (I-V) characteristics of a single nanowire display a linear behavior (Ohmic contact) from 300 K to 83 K with an average conductivity of 57.82 ± 4.8 S cm−1, a hole concentration of 5.98 × 1018 cm−3, and hole mobility of 60.33 cm2V−1S−1 at 300 K. The single porous nanowire not only displays resistivity of approximately five orders of magnitude lower than those of previous reported values but is also stable and insensitive to the environment’s effects. Moreover, conductivity of porous nanowires can be modulated via the doping or substituting mechanisms when encountering heavy metal ions. The single nanowire device is applied as an electrochemical sensor in detecting four metal ions (Cu2+, Co2+, Hg2+, and Fe3+). The wide dynamic range in electrical conductivity of this porous single nanowire makes it a potential candidate for metal ion sensing with great sensitivity.

The effect of nanoelectrodes number and length on enhancing the THz photomixer performance

Abstract: Despite the distinct features of the continuous wave (CW) Terahertz (THz) emitter using photomixing technique, it suffers from the relatively low radiation output power. Therefore, one of effective ways to improve the photomixer emitter performance was using nanodimensions electrodes inside the optical active region of the device. Due to the nanodimension sizes and good electrical conductivity of silver nanowires (Ag-NWs), they have been exploited as THz emitter electrodes. The excited surface plasmon polariton waves (SPPs) on the surface of nanowire enhances the incident excitation signal. Therefore, the photomixer based Ag-NW compared to conventional one significantly exhibits higher THz output signal. In this work, the effect of Ag-NWs dimensions and number on the incident optical field is investigated by utilizing the Computer Simulation Technology (CST) Studio Suite. The simulation results show that increasing Ag-NWs length to SPP propagation length ratio plays a significant role on the incident field increment due to its effect on reducing the SPP propagation losses. The increment of Ag-NWs number and length in the nanoelectrodes based photomixer can contribute to increase the electric field in the active region by 1.5 times at the longer excitation wavelength (850 nm). As a result of this increment, the THz output power and the conversion efficiency are expected to be enhanced by a factor of five

Flexible, anisotropic strain sensor based on interdigital capacitance for multi-direction discrimination

The direction information of strain plays a pivotal role in practical applications such as soft robots and human-machine interfaces. However, most of the multi-directional strain sensors studied before are integrated devices, which accomplish the strain direction discrimination through the signal difference of independent sensing units when they are stretched, thus increasing the complexity of the detection system. In this article, a multi-directional flexible strain sensor based on an interdigital capacitance structure is reported. The structure enables opposite variation of the capacitance changes in the orthogonal direction because the device exhibits different structural deformation depending on the direction of strain, thus detecting multiple direction strain by a single device. This sensor is fabricated by a one-step transfer method, which takes advantage of the excellent electrical conductivity of silver nanowires and the extremely low surface adhesion of the release film. The strain range of this sensor can be up to 60%. The influence of the structural parameters of the sensor on the gauge factor (GF) is explored to optimize capacitance structure parameters. The device shows good stability dynamic response (0.1–1.0 Hz). When the angle of strain direction changes from 0° to 90°, the GF changes from 1.1 to -0.56. Furthermore, owing to the high sensitivity and excellent stability of the sensor, human motion such as the bending direction of the wrist, can be accurately detected by this sensor.

Thermal transport in kinked nanowires through simulation.

The thermal conductance of nanowires is an oft-explored quantity, but its dependence on the nanowire shape is not completely understood. The behaviour of the conductance is examined as kinks of varying angular intensity are included into nanowires. The effects on thermal transport are evaluated through molecular dynamics simulations, phonon Monte Carlo simulations and classical solutions of the Fourier equation. A detailed look is taken at the nature of heat flux within said systems. The effects of the kink angle are found to be complex, influenced by multiple factors including crystal orientation, details of transport modelling, and the ratio of mean free path to characteristic system lengths. The effect of varying phonon reflection specularity on the heat flux is also examined. It is found that, in general, the flow of heat through systems simulated through phonon Monte Carlo methods is concentrated into a channel smaller than the wire dimensions, while this is not the case in the classical solutions of the Fourier model.

The Tortuosity Effect on the Thermal Conductivity of Si Nanowires

ABSTRACT The thermal conductivity of tortuous silicon nanowires with constant cross section at room temperature was investigated in use of full-spectrum Monte-Carlo simulations. Various geometric features that can be possibly used to describe the tortuosity of the nanowires were studied and their relationships with the thermal conductivity were explored. Comparison of simulation results with experimental data shows similar magnitudes and variation trend of the thermal conductivity against the nanowire hydraulic diameter. The more tortuous, the smaller the thermal conductivity is. Among all, data collapse is best when shown against the surface-to-volume ratio and the correlation length of the surface roughness does not affect the thermal conductivity at all. By taking the surface-to-volume ratio into account for the boundary scattering rate, which also depends on the phonon frequency indirectly through the phonon group velocity, we are able to obtain satisfactory predictions based on a linear spectral model, not only about the thermal conductivity but also about the spectral heat flux density distribution. The model also shows that the relative reduction caused by tortuosity decreases with increasing frequency. For highly tortuous nanowires of diameter 22 nm, simply increasing the tortuosity is sufficient to obtain simulated thermal conductivities that are smaller than the experimentally measured value.

The Impact of Hydrostatic Pressure on Thermal Conductivity of Nanostructured Bi

In this study, a simulation of theoretical calculation of Lattice thermal conductivity of Bismuth bulk and nanowires with diameters of 98, 115, and 327 nm in the temperature range of 10 ‒ 300 K and pressure range of 0 ‒ 1.6 GPa was investigated. These calculations were achieved by using the Morelli Callaway model and the Clapeyron equation that both longitudinal and transverse modes are taken into account. Melting temperature, mass density, unit cell volume, mean bond length, lattice parameter, group velocity, and longitudinal and transverse Debye temperature for all transverse and longitudinal modes were calculated for each NW diameter mentioned.

Influence of tin oxide decoration on the junction conductivity of silver nanowires

Flexible electrodes using nanowires (NWs) suffer from challenges of long-term stability and high junction resistance which limit their fields of applications. Welding via thermal annealing is a common strategy to enhance the conductivity of percolated NW networks, however, it affects the structural and mechanical integrity of the NWs. In this study we show that the decoration of NWs with an ultrathin metal oxide is a potential alternative procedure which not only enhances the thermal and chemical stability but, moreover, provides a totally different mechanism to reduce the junction resistance upon heat treatment. Here, we analyze the effect of SnO x decoration on the conductance of silver NWs and NW junctions by using a four-probe measurement setup inside a scanning electron microscope. Dedicated transmission electron microscopy analysis in plan-view and cross-section geometry are carried out to characterize the nanowires and the microstructure of the junctions. Upon heat treatment the junction resistance of both plain silver NWs and SnO x -decorated NWs is reduced by around 80%. While plain silver NWs show characteristic junction welding during annealing, the SnO x -decoration reduces junction resistance by a solder-like process which does not affect the mechanical integrity of the NW junction and is therefore expected to be superior for applications.

Preparation method and application of silicon nanowires

In recent years, silicon nanowires have become a hot spot in the new material industry. As a kind of nanomaterial, silicon nanowires have excellent physical and chemical properties. However, the preparation method of silicon nanowires is not mature enough, which limits its further application. This paper mainly analyses the mechanism, advantages and disadvantages of several mainstream silicon nanowires preparation methods, and discusses the application of silicon nanowires and the future development direction. The results show that the chemical vapor deposition method can be used for large-scale preparation of silicon nanowires, while the laser ablation method can produce silicon nanowires with higher purity, and the electron beam lithography method has the advantages of high flexibility. However, the efficiency of these three methods is not high, and the cost is high, which is also the problem that the silicon nanowire preparation industry is looking forward to solve. Relying on the excellent conductivity, thermal conductivity and other characteristics of silicon nanowires, silicon nanowires can be applied to a variety of new energy industries. Based on the properties of silicon nanowires, this paper analyses the application of silicon nanowires in lithium batteries, solar cells, biosensors and thermoelectric materials in recent years, and forecasts its development trend, so as to provide a certain reference for researchers to further explore the research of silicon nanowires.

Structure of Geobacter cytochrome OmcZ identifies mechanism of nanowire assembly and conductivity.

OmcZ nanowires produced by Geobacter species have high electron conductivity (>30 S cm-1). Of 111 cytochromes present in G. sulfurreducens, OmcZ is the only known nanowire-forming cytochrome essential for the formation of high-current-density biofilms that require long-distance (>10 µm) extracellular electron transport. However, the mechanisms underlying OmcZ nanowire assembly and high conductivity are unknown. Here we report a 3.5-Å-resolution cryogenic electron microscopy structure for OmcZ nanowires. Our structure reveals linear and closely stacked haems that may account for conductivity. Surface-exposed haems and charge interactions explain how OmcZ nanowires bind to diverse extracellular electron acceptors and how organization of nanowire network re-arranges in different biochemical environments. In vitro studies explain how G. sulfurreducens employ a serine protease to control the assembly of OmcZ monomers into nanowires. We find that both OmcZ and serine protease are widespread in environmentally important bacteria and archaea, thus establishing a prevalence of nanowire biogenesis across diverse species and environments.

Enhanced phonon resonance by non-uniform surface nanopillars in Si nanowires

Based on the wave nature of phonons, the lattice thermal conductivity of nanowires can be regulated by phonon resonators such as surface nanopillars. In this study, the impact of the height and distance of the resonant nanopillars on the thermal conductivity of Si nanowires were investigated. The results calculated from the molecular dynamics simulations show that with increasing height of the nanopillars, the corresponding thermal conductivity decreases. We found that the nanopillars with non-uniform heights induce stronger phonon resonance effect and can further suppress the thermal conductivity, as compared to the models with nanopillars of uniform heights. On the other hand, changing the distance between two adjacent nanopillars does not obviously affect the phonon propagation. Phonon dispersion relations show the formation of flat bands, which confirms the occurrence of phonon resonances due to the nanopillars. When the heights of the nanopillars become non-uniform, more flat bands were generated, and the phonon group velocity further decreased. Analyses of phonon participation ratio indicate stronger phonon localization induced by the disorder stemming from the non-uniform nanopillar height. Our investigation yields new insights into the physical mechanisms governing heat transport in nanowires with phonon resonators, and thus opens potential new routes to the design of thermoelectric devices.

Tuning interfacial thermal conductance of GaN/AlN heterostructure nanowires by constructing core/shell structure

The ability to tune the interfacial thermal conductance of GaN/AlN heterojunction nanowires (NWs) with a core/shell structure is shown using molecular dynamics and non-equilibrium Green’s functions method. In particular, an increase in the shell thickness leads to a significant improvement of interfacial thermal conductance of GaN/AlN core/shell NWs. At room temperature (300 K), the interfacial thermal conductance of NWs with specific core/shell ratio can reach 0.608 nW K−1, which is about twice that of GaN/AlN heterojunction NWs due to the weak phonon scattering and phonon localization. Moreover, changing the core/shell type enables one to vary interfacial thermal conductance relative to that of GaN/AlN heterojunction NWs. The results of the study provide an important guidance for solving the thermal management problems of GaN-based devices.

Impact of Ge clustering on the thermal conductivity of SiGe nanowires: atomistic simulation study.

Using non-equilibrium molecular dynamics simulations, we demonstrate that the thermal conductivity of SiGe alloy nanowires is remarkably sensitive to inhomogeneous composition distributions. Specifically, the effects of Ge clustering on the thermal conductivity of SiGe nanowires are studied. The results showed that clustering Ge atoms can improve the thermal conductivity of SiGe alloy nanowires due to the reduction of random alloy scattering centers. When the number of Ge atoms in the nanocluster increases, the thermal conductivity of such nanowires grows monotonically compared with that of random alloy nanowires. To reveal the role of inhomogeneous Ge distributions on the thermal conductivity, we performed vibrational eigenmode analyses and found the remarkable delocalization of phonon modes after Ge clustering. Through such analyses, we found that the increase in thermal conductivity was correlated with the phonon delocalization in the SiGe nanowires, where stronger delocalization indicates a better thermal performance of the nanowires. Our results are helpful not only in understanding the clustering effects on heat transport but also in modulating the thermal conductivity of SiGe nanowires.

Effects of vacancies on the thermal conductivity of Si nanowires.

Point defects can be used to tailor the properties of semiconductors, but can also have undesired effects on electronic and thermal transport, particularly in ultrascaled nanostructures, such as nanowires. Here we use all-atom molecular dynamics to study the effect that different concentrations and spatial distributions of vacancies have on the thermal conductivity of Si nanowires, overcoming the limitations of previous studies. Although vacancies are not as effective as the nanovoids found in e.g. porous Si, they can still reduce the thermal conductivity in ultrathin Si nanowires by more than a factor of two, when found in concentrations smaller than 1%. We also present arguments against the so-called self-purification mechanism, which is sometimes suggested to take place and proposes that vacancies have no influence on transport phenomena in nanowires.

Electrical conductivity of diene and pheneMolecular Nanowires: A QTAIM approach

Electrical conductivity of diene and pheneMolecular Nanowires: A QTAIM approach