Showing papers on "Nanowire published in 2008"

Enhanced thermoelectric performance of rough silicon nanowires

Abstract: Approximately 90 per cent of the world's power is generated by heat engines that use fossil fuel combustion as a heat source and typically operate at 30-40 per cent efficiency, such that roughly 15 terawatts of heat is lost to the environment. Thermoelectric modules could potentially convert part of this low-grade waste heat to electricity. Their efficiency depends on the thermoelectric figure of merit ZT of their material components, which is a function of the Seebeck coefficient, electrical resistivity, thermal conductivity and absolute temperature. Over the past five decades it has been challenging to increase ZT > 1, since the parameters of ZT are generally interdependent. While nanostructured thermoelectric materials can increase ZT > 1 (refs 2-4), the materials (Bi, Te, Pb, Sb, and Ag) and processes used are not often easy to scale to practically useful dimensions. Here we report the electrochemical synthesis of large-area, wafer-scale arrays of rough Si nanowires that are 20-300 nm in diameter. These nanowires have Seebeck coefficient and electrical resistivity values that are the same as doped bulk Si, but those with diameters of about 50 nm exhibit 100-fold reduction in thermal conductivity, yielding ZT = 0.6 at room temperature. For such nanowires, the lattice contribution to thermal conductivity approaches the amorphous limit for Si, which cannot be explained by current theories. Although bulk Si is a poor thermoelectric material, by greatly reducing thermal conductivity without much affecting the Seebeck coefficient and electrical resistivity, Si nanowire arrays show promise as high-performance, scalable thermoelectric materials.

Silicon nanowires as efficient thermoelectric materials

Abstract: Thermoelectric materials, capable of converting a thermal gradient to an electric field and vice versa, could be useful in power generation and refrigeration. But the fabrication of the available high-performance thermoelectric materials is not easily scaled up to the volumes needed for large-scale heat energy scavenging applications. Nanostructuring improves thermoelectric capabilities of some materials, but good thermoelectric materials tend not to take readily to nanostructuring. How about silicon? It can be processed on a large scale but has poor thermoelectric properties. Two groups now show that silicon's thermoelectric properties can be vastly improved by structuring it into arrays of nanowires and carefully controlling nanowire morphology and doping. So with more development, silicon may have potential as a thermoelectric material. Thermoelectric materials interconvert thermal gradients and electric fields for power generation or for refrigeration1,2. Thermoelectrics currently find only niche applications because of their limited efficiency, which is measured by the dimensionless parameter ZT—a function of the Seebeck coefficient or thermoelectric power, and of the electrical and thermal conductivities. Maximizing ZT is challenging because optimizing one physical parameter often adversely affects another3. Several groups have achieved significant improvements in ZT through multi-component nanostructured thermoelectrics4,5,6, such as Bi2Te3/Sb2Te3 thin-film superlattices, or embedded PbSeTe quantum dot superlattices. Here we report efficient thermoelectric performance from the single-component system of silicon nanowires for cross-sectional areas of 10 nm × 20 nm and 20 nm × 20 nm. By varying the nanowire size and impurity doping levels, ZT values representing an approximately 100-fold improvement over bulk Si are achieved over a broad temperature range, including ZT ≈ 1 at 200 K. Independent measurements of the Seebeck coefficient, the electrical conductivity and the thermal conductivity, combined with theory, indicate that the improved efficiency originates from phonon effects. These results are expected to apply to other classes of semiconductor nanomaterials.

Solution-processed metal nanowire mesh transparent electrodes.

Abstract: Transparent conductive electrodes are important components of thin-film solar cells, light-emitting diodes, and many display technologies. Doped metal oxides are commonly used, but their optical transparency is limited for films with a low sheet resistance. Furthermore, they are prone to cracking when deposited on flexible substrates, are costly, and require a high-temperature step for the best performance. We demonstrate solution-processed transparent electrodes consisting of random meshes of metal nanowires that exhibit an optical transparency equivalent to or better than that of metal-oxide thin films for the same sheet resistance. Organic solar cells deposited on these electrodes show a performance equivalent to that of devices based on a conventional metal-oxide transparent electrode.

Vertically aligned single crystal TiO2 nanowire arrays grown directly on transparent conducting oxide coated glass: synthesis details and applications

Abstract: Single-crystal one-dimensional (1D) semiconductor architectures are important in materials-based applications requiring a large surface area, morphological control, and superior charge transport. Titania has widespread utility in applications including photocatalysis, photochromism, photovoltaics, and gas sensors. While considerable efforts have focused on the preparation of 1D TiO2, no methods have been available to grow crystalline nanowire arrays directly onto transparent conducting oxide (TCO) substrates, greatly limiting the performance of TiO2 photoelectrochemical devices. Herein, we present a straightforward low temperature method to prepare single crystal rutile TiO2 nanowire arrays up to 5 microm long on TCO glass via a non-polar solvent/hydrophilic substrate interfacial reaction under mild hydrothermal conditions. The as-prepared densely packed nanowires grow vertically oriented from the TCO glass substrate along the (110) crystal plane with a preferred (001) orientation. In a dye sensitized solar cell, N719 dye, using TiO2 nanowire arrays 2-3 microm long we achieve an AM 1.5 photoconversion efficiency of 5.02%.

High Capacity Li Ion Battery Anodes Using Ge Nanowires

Abstract: Ge nanowire electrodes fabricated by using vapor−liquid−solid growth on metallic current collector substrates were found to have good performance during cycling with Li. An initial discharge capacity of 1141 mA·h/g was found to be stable over 20 cycles at the C/20 rate. High power rates were also observed up to 2C with Coulombic efficiency > 99%. Structural characterization revealed that the Ge nanowires remain intact and connected to the current collector after cycling. Nanowires connected directly to the current collector have facile strain relaxation and material durability, short Li diffusion distances, and good electronic conduction. Thus, Ge nanowire anodes are promising candidates for the development of high-energy-density lithium batteries.

Multi-quantum-well nanowire heterostructures for wavelength-controlled lasers.

Abstract: Rational design and synthesis of nanowires with increasingly complex structures can yield enhanced and/or novel electronic and photonic functions. For example, Ge/Si core/shell nanowires have exhibited substantially higher performance as field-effect transistors and low-temperature quantum devices compared with homogeneous materials, and nano-roughened Si nanowires were recently shown to have an unusually high thermoelectric figure of merit. Here, we report the first multi-quantum-well (MQW) core/shell nanowire heterostructures based on well-defined III-nitride materials that enable lasing over a broad range of wavelengths at room temperature. Transmission electron microscopy studies show that the triangular GaN nanowire cores enable epitaxial and dislocation-free growth of highly uniform (InGaN/GaN)n quantum wells with n=3, 13 and 26 and InGaN well thicknesses of 1-3 nm. Optical excitation of individual MQW nanowire structures yielded lasing with InGaN quantum-well composition-dependent emission from 365 to 494 nm, and threshold dependent on quantum well number, n. Our work demonstrates a new level of complexity in nanowire structures, which potentially can yield free-standing injection nanolasers.

Current-controlled magnetic domain-wall nanowire shift register.

Abstract: The controlled motion of a series of domain walls along magnetic nanowires using spin-polarized current pulses is the essential ingredient of the proposed magnetic racetrack memory, a new class of potential non-volatile storage-class memories. Using permalloy nanowires, we achieved the successive creation, motion, and detection of domain walls by using sequences of properly timed, nanosecond-long, spin-polarized current pulses. The cycle time for the writing and shifting of the domain walls was a few tens of nanoseconds. Our results illustrate the basic concept of a magnetic shift register that relies on the phenomenon of spin-momentum transfer to move series of closely spaced domain walls.

Gas sensing properties of defect-controlled ZnO-nanowire gas sensor

Abstract: The effect of oxygen-vacancy-related defects on gas-sensing properties of ZnO-nanowire gas sensors was investigated. Gas sensors were fabricated by growing ZnO nanowires bridging the gap between two prepatterned Au catalysts. The sensor displayed fast response and recovery behavior with a maximum sensitivity to NO2 gas at 225 °C. Gas sensitivity was found to be linearly proportional to the photoluminescence intensity of oxygen-vacancy-related defects in both as-fabricated and defect-controlled gas sensors by postannealing in Ar and H2 atmosphere. This result agrees well with previous theoretical prediction that oxygen vacancies play a role of preferential adsorption sites for NO2 molecules.

Twinning superlattices in indium phosphide nanowires

Abstract: In most superconductors, the pairing-up of electrons responsible for resistance-free conductivity is driven by vibrations of the solid's crystal lattice. But there are other superconducting materials in which the 'glue' responsible for binding electrons is thought to have a very different origin: quantum fluctuations of spin or charge. An unusually 'violent' generalization of such a pairing mechanisms, in which spin and charge instabilities combine forces, has been identified in the unconventional superconductor CeRhIn5. These intimately coupled fluctuations significantly disrupt the flow of electrons in their normal unpaired state, yet also provide the quantum-mechanical glue necessary for generating superconducting pairs. In this paper, the crystal structure and stacking fault density of semiconducting nanowires composed of the same material are controlled by doping, leading to twinning superlattices. Periodic arrays of rotational dislocations lead to crystal heterostructures in indium phosphide and gallium phosphide nanowires. Semiconducting nanowires offer the possibility of nearly unlimited complex bottom-up design1,2, which allows for new device concepts3,4. However, essential parameters that determine the electronic quality of the wires, and which have not been controlled yet for the III–V compound semiconductors, are the wire crystal structure and the stacking fault density5. In addition, a significant feature would be to have a constant spacing between rotational twins in the wires such that a twinning superlattice is formed, as this is predicted to induce a direct bandgap in normally indirect bandgap semiconductors6,7, such as silicon and gallium phosphide. Optically active versions of these technologically relevant semiconductors could have a significant impact on the electronics8 and optics9 industry. Here we show first that we can control the crystal structure of indium phosphide (InP) nanowires by using impurity dopants. We have found that zinc decreases the activation barrier for two-dimensional nucleation growth of zinc-blende InP and therefore promotes crystallization of the InP nanowires in the zinc-blende, instead of the commonly found wurtzite, crystal structure10. More importantly, we then demonstrate that we can, once we have enforced the zinc-blende crystal structure, induce twinning superlattices with long-range order in InP nanowires. We can tune the spacing of the superlattices by changing the wire diameter and the zinc concentration, and we present a model based on the distortion of the catalyst droplet in response to the evolution of the cross-sectional shape of the nanowires to quantitatively explain the formation of the periodic twinning.

MnO2/poly(3,4-ethylenedioxythiophene) coaxial nanowires by one-step coelectrodeposition for electrochemical energy storage.

Abstract: We introduce a simple one-step method to synthesize MnO2/poly(3,4-ethylenedioxythiophene) (PEDOT) coaxial nanowires by coelectrodeposition in a porous alumina template. Constant potential (typically 0.75 V vs Ag/AgCl) is applied on the bottom electrodes in the pores of the alumina template in aqueous solution containing manganese acetate (10 mM) and EDOT monomers (80 mM). We can easily control the structures of coaxial nanowires such as PEDOT shell thickness and nanowire length by varying the applied potential. Electrochemical properties of the coaxial nanowires were investigated for an electrochemical supercapacitor. Coaxial nanowires not only exhibit high specific capacitance values but also maintain them well at high current density. The well-maintained specific capacitance is mainly due to short paths of ion diffusion in the nanowires. Therefore, even at high current density (high power demand), the nanowire materials can be fully utilized. The porous nature of the PEDOT shell allows such fast ion dif...

High-resolution detection of Au catalyst atoms in Si nanowires

Abstract: The potential for the metal nanocatalyst to contaminate vapour–liquid–solid grown semiconductor nanowires has been a long-standing concern, because the most common catalyst material, Au, is highly detrimental to the performance of minority carrier electronic devices. We have detected single Au atoms in Si nanowires grown using Au nanocatalyst particles in a vapour–liquid–solid process. Using high-angle annular dark-field scanning transmission electron microscopy, Au atoms were observed in higher numbers than expected from a simple extrapolation of the bulk solubility to the low growth temperature. Direct measurements of the minority carrier diffusion length versus nanowire diameter, however, demonstrate that surface recombination controls minority carrier transport in as-grown n-type nanowires; the influence of Au is negligible. These results advance the quantitative correlation of atomic-scale structure with the properties of nanomaterials and can provide essential guidance to the development of nanowire-based device technologies.

Photovoltaic Measurements in Single-Nanowire Silicon Solar Cells

Abstract: Single-nanowire solar cells were created by forming rectifying junctions in electrically contacted vapor-liquid-solid-grown Si nanowires. The nanowires had diameters in the range of 200 nm to 1.5 microm. Dark and light current-voltage measurements were made under simulated Air Mass 1.5 global illumination. Photovoltaic spectral response measurements were also performed. Scanning photocurrent microscopy indicated that the Si nanowire devices had minority carrier diffusion lengths of approximately 2 microm. Assuming bulk-dominated recombination, this value corresponds to a minimum carrier lifetime of approximately 15 ns, or assuming surface-dominated recombination, to a maximum surface recombination velocity of approximately 1350 cm s(-1). The methods described herein comprise a valuable platform for measuring the properties of semiconductor nanowires, and are expected to be instrumental when designing an efficient macroscopic solar cell based on arrays of such nanostructures.

Wafer-scale assembly of highly ordered semiconductor nanowire arrays by contact printing.

Abstract: Controlled and uniform assembly of “bottom-up” nanowire (NW) materials with high scalability presents one of the significant bottleneck challenges facing the integration of nanowires for electronic...

Growth of nanowires

Abstract: The tremendous interest in nanoscale structures such as quantum dots (zero-dimension) and wires (quasi-one-dimension) stems from their size-dependent properties. One-dimensional (1D) semiconductor nanostructures are of particular interest because of their potential applications in nanoscale electronic and optoelectronic devices. For 1D semiconductor nanomaterials to have wide practical application, however, several areas require further development. In particular, the fabrication of desired 1D nanomaterials with tailored atomic structures and their assembly into functional devices are still major challenges for nanotechnologists. In this review, we focus on the status of research on the formation of nanowire structures via highly anisotropic growth of nanocrystals of semiconductor and metal oxide materials with an emphasis on the structural characterization of the nucleation, initial growth, defects and interface structures, as well as on theoretical analyses of nanocrystal formation, reactivity and stability. We review various methods used and mechanisms involved to generate 1D nanostructures from different material systems through self-organized growth techniques including vapor–liquid–solid growth, oxide-assisted chemical vapor deposition (without a metal catalyst), laser ablation, thermal evaporation, metal-catalyzed molecular beam epitaxy, chemical beam epitaxy and hydrothermal reaction. 1D nanostructures grown by these technologies have been observed to exhibit unusual growth phenomena and unexpected properties, e.g., diameter-dependent and temperature-dependent growth directions, structural transformation by enhanced photothermal effects and phase transformation induced by the point contact reaction in ultra-thin semiconductor nanowires. Recent progress in controlling growth directions, defects, interface structures, structural transformation, contacts and hetero-junctions in 1D nanostructures is addressed. Also reviewed are the quantitative explorations and predictions of some challenging 1D nanostructures and descriptions of the growth mechanisms of 1D nanostructures, based on the energetic, dynamic and kinetic behaviors of the building block nanostructures and their surfaces and/or interfaces.

Surface Effect on the Elastic Behavior of Static Bending Nanowires

Abstract: The surface effect from surface stress and surface elasticity on the elastic behavior of nanowires in static bending is incorporated into Euler-Bernoulli beam theory via the Young-Laplace equation. Explicit solutions are presented to study the dependence of the surface effect on the overall Young's modulus of nanowires for three different boundary conditions: cantilever, simply supported, and fixed-fixed. The solutions indicate that the cantilever nanowires behave as softer materials when deflected while the other structures behave like stiffer materials as the nanowire cross-sectional size decreases for positive surface stresses. These solutions agree with size dependent nanowire overall Young's moduli observed from static bending tests by other researchers. This study also discusses possible reasons for variations of nanowire overall Young's moduli observed.

Preparation of Large-Area Uniform Silicon Nanowires Arrays through Metal-Assisted Chemical Etching

Abstract: A facile fabricating method has been established for large-area uniform silicon nanowires arrays All silicon nanowires obtained were single crystals and epitaxial on the substrate Six kinds of silicon wafers with different types, surface orientations, and doping levels were utilized as starting materials With the catalysis of silver nanoparticles, room-temperature mild chemical etching was conducted in aqueous solution of hydrofluoric acid (HF) and hydrogen peroxide (H2O2) The corresponding silicon nanowires arrays with different morphologies were obtained The silicon nanowires possess the same type and same doping level of the starting wafer All nanowires on the substrate have the same orientation For instance, both (100)- and (111)-oriented p-type wafers produced silicon nanowires in the (100) direction For every kind of silicon wafer, the effect of etching conditions, such as components of etchant, temperature, and time, were systemically investigated This is an appropriate method to produce a

Sub-two nanometer single crystal Au nanowires

Abstract: Ultrathin single crystal Au nanowires with diameter of approximately 1.6 nm and length of few micrometers were synthesized with high yield by simply mixing HAuCl 4 and oleylamine at room temperature. High resolution transmission electron microscopy studies revealed that all of these nanowires are single crystalline and grew along the [111] direction. The valency evolution of the gold species during the synthesis was studied by X-ray photoelectron spectroscopy, which showed a clear Au (3+) --> Au (+) --> Au stepwise reduction at different reaction stages. Small angle X-ray scattering and small-angle X-ray diffraction suggest mesostructure formation upon HAuCl 4 and oleylamine mixing. The slow in situ reduction of this mesostructure leads to the formation of ultrathin nanowires in solution. This novel nanowire growth mechanism relies on cooperative interaction, organization, and reaction between inorganic precursor salts and oleylamine.

Electronic properties of semiconductor nanowires.

Abstract: This paper provides a review of the state-of-the-art electronic-structure calculations of semiconductor nanowires. Results obtained using empirical k.p, empirical tight-binding, semi-empirical pseudopotential, and with ab initio methods are compared. For conciseness, we will restrict our detailed discussions to free-standing plain and modulated nanowires. Connections to relevant experimental data, particularly band gaps and polarization anisotropy, will be made since these results depend crucially on the electronic properties. For completeness, a brief review on the synthesis of nanowires is included.

Dislocation-Driven Nanowire Growth and Eshelby Twist

Abstract: Hierarchical nanostructures of lead sulfide nanowires resembling pine trees were synthesized by chemical vapor deposition. Structural characterization revealed a screwlike dislocation in the nanowire trunks with helically rotating epitaxial branch nanowires. It is suggested that the screw component of an axial dislocation provides the self-perpetuating steps to enable one-dimensional crystal growth, in contrast to mechanisms that require metal catalysts. The rotating trunks and branches are the consequence of the Eshelby twist of screw dislocations with a dislocation Burgers vector along the 〈110〉 directions having an estimated magnitude of 6 ± 2 angstroms for the screw component. The results confirm the Eshelby theory of dislocations, and the proposed nanowire growth mechanism could be general to many materials.

Design of light scattering in nanowire materials for photovoltaic applications

Abstract: We experimentally investigate the optical properties of layers of InP, Si, and GaP nanowires, relevant for applications in solar cells. The nanowires are strongly photonic, resulting in a significant coupling mismatch with incident light due to multiple scattering. We identify a design principle for the effective suppression of reflective losses, based on the ratio of the nondiffusive absorption and diffusive scattering lengths. Using this principle, we demonstrate successful suppression of the hemispherical diffuse reflectance of InP nanowires to below that of the corresponding transparent effective medium. The design of light scattering in nanowire materials is of large importance for optimization of the external efficiency of nanowire-based photovoltaic devices.

Functionalization of Electrospun TiO2 Nanofibers with Pt Nanoparticles and Nanowires for Catalytic Applications

Abstract: This paper reports a simple procedure for derivatizing the surface of anatase TiO2 nanofibers with Pt nanoparticles and then Pt nanowires. The nanofibers were prepared in the form of a nonwoven mat by electrospinning with a solution containing both poly(vinyl pyrrolidone) and titanium tetraisopropoxide, followed by calcination in air at 510 degrees C. The fiber mat was then immersed in a polyol reduction bath to coat the surface of anatase fibers with Pt nanoparticles of 2-5 nm in size with controllable density of coverage. Furthermore, the coated fibers could serve as a three-dimensional scaffold upon which Pt nanowires of roughly 7 nm in diameter could be grown at a high density and with a length up to 125 nm. The fiber membranes functionalized with Pt nanoparticles and nanowires are interesting for a number of catalytic applications. It was found to show excellent catalytic activity for the hydrogenation of azo bonds in methyl red, which could be operated in a continuous mode by passing the dye solution through the membrane at a flow rate of 0.5 mL/s.

Ultrathin gold nanowires can be obtained by reducing polymeric strands of oleylamine-AuCl complexes formed via aurophilic interaction.

Abstract: This Communication describes a facile route to the preparation of ultrathin gold nanowires using linear chains formed from [(oleylamine)AuCl] complex via aurophilic interaction. The linear chains, with AuI···AuI bonds as the backbone and surrounded by oleylamines, can group together to form bundles of polymeric strands. When the AuI was reduced to Au0 by reacting with Ag nanoparticles in hexane, the polymeric strands functioned as both the source of Au and the template to mediate the nucleation and growth of Au nanowires. Using this method, we were able to produce Au nanowires with an average diameter of ∼1.8 nm and an aspect ratio of >1000 in high yields (∼70%).

Single and tandem axial p-i-n nanowire photovoltaic devices.

Abstract: Nanowires represent a promising class of materials for exploring new concepts in solar energy conversion. Here we report the first experimental realization of axial modulation-doped p-i-n and tandem p-i-n(+) -p(+)-i-n silicon nanowire (SiNW) photovoltaic elements. Scanning electron microscopy images of selectively etched nanowires demonstrate excellent synthetic control over doping and lengths of distinct regions in the diode structures. Current-voltage (I-V) characteristics reveal clear and reproducible diode characteristics for the p-i-n and p-n SiNW devices. Under simulated one-sun solar conditions (AM 1.5G), optimized p-i-n SiNW devices exhibited an open circuit voltage (Voc) of 0.29 V, a maximum short-circuit current density of 3.5 mA/cm(2), and a maximum efficiency of 0.5%. The response of the short-circuit current versus Voc under varying illumination intensities shows that the diode quality factor is improved from n=1.78 to n=1.28 by insertion of the i-type SiNW segment. The temperature dependence of Voc scales as -2.97 mV/K and extrapolates to the crystalline Si band gap at 0 K, which is in excellent agreement with bulk properties. Finally, a novel single SiNW tandem solar cell consisting of synthetic integration of two photovoltaic elements with an overall p-i-n(+) -p(+)-i-n structure was prepared and shown to exhibit a Voc that is on average 57% larger than that of the single p-i-n device. Fundamental studies of such well-defined nanowire photovoltaics will enable their intrinsic performance limits to be defined.

Enhanced Thermoelectric Performance of Rough Silicon Nanowires.

Abstract: Approximately 90 per cent of the world's power is generated by heat engines that use fossil fuel combustion as a heat source and typically operate at 30-40 per cent efficiency, such that roughly 15 terawatts of heat is lost to the environment. Thermoelectric modules could potentially convert part of this low-grade waste heat to electricity. Their efficiency depends on the thermoelectric figure of merit ZT of their material components, which is a function of the Seebeck coefficient, electrical resistivity, thermal conductivity and absolute temperature. Over the past five decades it has been challenging to increase ZT > 1, since the parameters of ZT are generally interdependent. While nanostructured thermoelectric materials can increase ZT > 1 (refs 2-4), the materials (Bi, Te, Pb, Sb, and Ag) and processes used are not often easy to scale to practically useful dimensions. Here we report the electrochemical synthesis of large-area, wafer-scale arrays of rough Si nanowires that are 20-300 nm in diameter. These nanowires have Seebeck coefficient and electrical resistivity values that are the same as doped bulk Si, but those with diameters of about 50 nm exhibit 100-fold reduction in thermal conductivity, yielding ZT = 0.6 at room temperature. For such nanowires, the lattice contribution to thermal conductivity approaches the amorphous limit for Si, which cannot be explained by current theories. Although bulk Si is a poor thermoelectric material, by greatly reducing thermal conductivity without much affecting the Seebeck coefficient and electrical resistivity, Si nanowire arrays show promise as high-performance, scalable thermoelectric materials.

Ultrathin Au nanowires and their transport properties.

Abstract: This paper presents a facile synthesis of single-crystalline Au nanowires by reduction of HAuCl4 in oleic acid and oleylamine. The diameter of these micron-meter-long Au nanowires is controlled to be 3 and 9 nm by volume ratio of oleylamine and oleic acid. When linked between two gold electrodes, the 9 nm Au nanowire shows good electron conductivity with its breakdown current density reaching 3.5 × 1012 A/m2. This demonstrates that the chemically made ultrathin Au nanowires can be used as a molecular-scale interconnect for nanoelectronic applications.

A Review on the Electrochemical Sensors and Biosensors Composed of Nanowires as Sensing Material.

Abstract: The development and application of nanowires for electrochemical sensors and biosensors are reviewed in this article. Next generation sensor platforms will require significant improvements in sensitivity, specificity and parallelism in order to meet the future needs in variety of fields. Sensors made of nanowires exploit some fundamental nanoscopic effect in order to meet these requirements. Nanowires are new materials, which have the characteristic of low weight with extraordinary mechanical, electrical, thermal and multifunctional properties. The advantages such as size scale, aspect ratio and other properties of nanowires are especially apparent in the use of electrical sensors such as electrochemical sensors and in the use of field-effect transistors. The preparation methods of nanowires and their properties are discussed along with their advantages towards electrochemical sensors and biosensors. Some key results from each article are summarized, relating the concept and mechanism behind each sensor, with experimental conditions as well as their behavior at different conditions.

An improved sensitivity non-enzymatic glucose sensor based on a CuO nanowire modified Cu electrode

Abstract: CuO nanowires have been prepared and applied for the fabrication of glucose sensors with highly enhanced sensitivity. Cu(OH)(2) nanowires were initially synthesised by a simple and fast procedure, CuO nanowires were then formed simply by removing the water through heat treatment. The structures and morphologies of Cu(OH)(2) and CuO nanowires were characterised by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The direct electrocatalytic oxidation of glucose in alkaline medium at CuO nanowire modified electrodes has been investigated in detail. Compared to a bare Cu electrode, a substantial decrease in the overvoltage of the glucose oxidation was observed at the CuO nanowire electrodes with oxidation starting at ca. 0.10 V vs. Ag/AgCl (saturated KCl). At an applied potential of 0.33 V, CuO nanowire electrodes produce high and reproducible sensitivity to glucose with 0.49 microA/micromol dm(-3). Linear responses were obtained over a concentration range from 0.40 micromol dm(-3) to 2.0 mmol dm(-3) with a detection limit of 49 nmol dm(-3) (S/N = 3). The CuO nanowire modified electrode allows highly sensitive, low working potential, stable, and fast amperometric sensing of glucose, thus is promising for the future development of non-enzymatic glucose sensors.

Silicon nanowires for rechargeable lithium-ion battery anodes

Abstract: Large-area, wafer-scale silicon nanowire arrays prepared by metal-induced chemical etching are shown as promising scalable anode materials for rechargeable lithium battery. In addition to being low cost, large area, and easy to prepare, the electroless-etched silicon nanowires (SiNWs) have good conductivity and nanometer-scale rough surfaces; both features facilitate charge transport and insertion/extraction of Li ions. The electroless-etched SiNWs anode showed larger charge capacity and longer cycling stability than the conventional planar-polished Si wafer.

Motility of metal nanoparticles in silicon and induced anisotropic silicon etching

Abstract: The autonomous motion behavior of metal particles in Si, and the consequential anisotropic etching of silicon and production of Si nanostructures, in particular, Si nanowire arrays in oxidizing hydrofluoric acid solution, has been systematically investigated. It is found that the autonomous motion of metal particles (Ag and Au) in Si is highly uniform, yet directional and preferential along the [100] crystallographic orientation of Si, rather than always being normal to the silicon surface. An electrokinetic model has been formulated, which, for the first time, satisfactorily explains the microscopic dynamic origin of motility of metal particles in Si. According to this model, the power generated in the bipolar electrochemical reaction at a metal particle's surface can be directly converted into mechanical work to propel the tunneling motion of metal particles in Si. The mechanism of pore and wire formation and their dependence on the crystal orientation are discussed. These models not only provide fundamental interpretation of metal-induced formation of pits, porous silicon, and silicon nanowires and nanopores, they also reveal that metal particles in the metal/Si system could work as a self-propelled nanomotor. Significantly, it provides a facile approach to produce various Si nanostructures, especially ordered Si nanowire arrays from Si wafers of desired properties.

Langmuir-Blodgettry of nanocrystals and nanowires.

Abstract: Although nanocrystals and nanowires have proliferated new scientific avenues in the study of their physics and chemistries, the bottom-up assembly of these small-scale building blocks remains a formidable challenge for device fabrication and processing. An attractive nanoscale assembly strategy should be cheap, fast, defect tolerant, compatible with a variety of materials, and parallel in nature, ideally utilizing the self-assembly to generate the core of a device, such as a memory chip or optical display. Langmuir−Blodgett (LB) assembly is a good candidate for arranging vast numbers of nanostructures on solid surfaces. In the LB technique, uniaxial compression of a nanocrystal or nanowire monolayer floating on an aqueous subphase causes the nanostructures to assemble and pack over a large area. The ordered monolayer can then be transferred to a solid surface en masse and with fidelity. In this Account, we present the Langmuir−Blodgett technique as a low-cost method for the massively parallel, controlled ...