Nanowire Clusters Research Articles

Growth of Aluminum Catalyzed AlGaAs Nanowires on Silicon Substrate

Aluminum catalyzed AlGaAs nanowires were fabricated on Si (111) substrates using metal-organic chemical vapor deposition (MOCVD) technique at a low growth temperature of 450 degrees C. Grown structures were characterized by field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDS) and photoluminescence (PL) techniques. Nanowire clusters were observed all over the substrate. Multiprong root-grown AlGaAs nanowire clusters as well as catalyst particle terminated growth was observed. The growth is explained by Vapor-Solid-Solid (VSS) and Vapor-Solid (VS) growth mechanisms using Al-Si binary phase diagram. EDS and PL measurement confirm the formation of AlGaAs nanowires.

Preparation and Growth Mechanism of Chrysanthemum-Like ZnO Nanowire Clusters

With sodium hydroxide (NaOH), ammonia water (NH3 x H2O) and hexamethylenetetramine (HMT, C6H12N4) respectively as alkaline source material, a simple hydrothermal process was employed to prepare chrysanthemum-like ZnO nanowire clusters. The morphologies and crystalline structures of the as-prepared products were investigated by X-ray diffractometer (XRD), field emission environment scanning electron microscope (SEM), and high-resolution transmission electron microscopy (TEM). The experimental results indicate that the as-prepared products all have three-dimensional chrysanthemum-like structure in which the petal-like nanowires are ZnO single crystalline with hexagonal wurtzite structure, that the flower bud saturation degree F(d) is slightly different under different alkaline source materials, and that the proposed growth mechanism of chrysanthemum-like ZnO nanowire clusters is reasonable.

High-performance supercapacitor and lithium-ion battery based on 3D hierarchical NH4F-induced nickel cobaltate nanosheet–nanowire cluster arrays as self-supported electrodes

A facile hydrothermal method is developed for large-scale production of three-dimensional (3D) hierarchical porous nickel cobaltate nanowire cluster arrays derived from nanosheet arrays with robust adhesion on Ni foam. Based on the morphology evolution upon reaction time, a possible formation process is proposed. The role of NH4F in formation of the structure has also been investigated based on different NH4F amounts. This unique structure significantly enhances the electroactive surface areas of the NiCo2O4 arrays, leading to better interfacial/chemical distributions at the nanoscale, fast ion and electron transfer and good strain accommodation. Thus, when it is used for supercapacitor testing, a specific capacitance of 1069 F g(-1) at a very high current density of 100 A g(-1) was obtained. Even after more than 10,000 cycles at various large current densities, a capacitance of 2000 F g(-1) at 10 A g(-1) with 93.8% retention can be achieved. It also exhibits a high-power density (26.1 kW kg(-1)) at a discharge current density of 80 A g(-1). When used as an anode material for lithium-ion batteries (LIBs), it presents a high reversible capacity of 976 mA h g(-1) at a rate of 200 mA g(-1) with good cycling stability and rate capability. This array material is rarely used as an anode material. Our results show that this unique 3D hierarchical porous nickel cobaltite is promising for electrochemical energy applications.

Effect of Sb-doping on the morphology and dielectric properties of chrysanthemum-like ZnO nanowire clusters

Chrysanthemum-like ZnO nanowire clusters with different Sb-doping concentrations were prepared using a hydrothermal process. The microstructures, morphologies, and dielectric properties of the as-prepared products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field emission environment scanning electron microscope (FEESEM), and microwave vector network analyzer respectively. The results indicate that the as-prepared products are Sb-doped ZnO single crystallines with a hexagonal wurtzite structure, the flower bud saturation degree Fd is obviously different from that of the pure ZnO nanowire clusters, the good dielectric loss property is found in Sb-doped ZnO products with low density, and the dielectric loss tangent tanδe increases with the increase of the Sb-doping concentration in a certain concentration range.

Substrate-Assisted Self-Organization of Radial β-AgVO3Nanowire Clusters for High Rate Rechargeable Lithium Batteries

Rational assembly of unique complex nanostructures is one of the facile techniques to improve the electrochemical performance of electrode materials. Here, a substrate-assisted hydrothermal method was designed and applied in synthesizing moundlily like radial β-AgVO(3) nanowire clusters. Gravitation and F(-) ions have been demonstrated to play important roles in the growth of β-AgVO(3) nanowires (NWs) on substrates. The results of cyclic voltammetry (CV) measurement and X-ray diffraction (XRD) characterization proved the phase transformation from β-AgVO(3) to Ag(1.92)V(4)O(11) during the redox reaction. Further electrochemical investigation showed that the moundlily like β-AgVO(3) nanowire cathode has a high discharge capacity and excellent cycling performance, mainly due to the reduced self-aggregation. The capacity fading per cycle from 3rd to 51st is 0.17% under the current density of 500 mA/g, which is much better than 1.46% under that of 20 mA/g. This phenomenon may be related to the Li(+) diffusion and related kinetics of the electrode. This method is shown to be an effective and facile technique for improving the electrochemical performance for applications in rechargeable Li batteries or Li ion batteries.

Self‐Supported Interconnected Pt Nanoassemblies as Highly Stable Electrocatalysts for Low‐Temperature Fuel Cells

In it for the long haul: Clusters of Pt nanowires (3D Pt nanoassemblies, Pt NA) serve as an electrocatalyst for low-temperature fuel cells. These Pt nanoassemblies exhibit remarkably high stability following thousands of voltage cycles and good catalytic activity, when compared with a commercial Pt catalyst and 20 % wt Pt catalyst supported on carbon black (20 % Pt/CB).

Modulation of surface wettability of superhydrophobic substrates using Si nanowire arrays and capillary-force-induced nanocohesion

We describe a new scalable method to fabricate large-area hybrid superhydrophobic surfaces with selective adhesion properties on silicon (Si) nanowire array substrates by exploiting liquid-medium-dependent capillary-force-induced nanocohesion. Gold (Au) nanoparticles were deposited on Si by glancing angle deposition followed by metal-assisted chemical etching of Si to form Si nanowire arrays. The surfaces were dried in either deionized (DI) water, 2-propanol or methanol to vary the capillary forces exerted on the Si nanowires during the drying process in order to tune the extent of clustering of nanowires and hence the adhesion properties of the resulting superhydrophobic surfaces. Here, we exploit the combined effects of surface tension and Young's contact angle to modulate the degree of clustering of the Si nanowires during capillary-force-induced nanocohesion. These surfaces were chemically modified and rendered hydrophobic by fluorosilane deposition. Drying in DI water resulted in small clusters of nanowires which produce a low-hysteresis superhydrophobic surface that mimics a lotus leaf. Drying in methanol resulted in large nanowire clusters that lead to a high-hysteresis superhydrophobic surface. Further, we demonstrate the ability to fabricate both small and large nanowire clusters by controlling the drying of the nanowire arrays in order to selectively define and modulate adhesion of water on the same superhydrophobic substrate. The simplicity of our process to tune surface wettability on single substrates paves the way for future applications in lab-on-chip devices and platforms for chemical and biological analyses.

Transformation of hydrothermally derived nanowire cluster intermediates into CdSiO3 nanobelts

In this communication, we demonstrate that cadmium metasilicate nanobelts could be fabricated via a facile, eco-friendly, low cost hydrothermal treatment in the absence of surfactants and organic additives, followed by calcination. The monoclinic phase formation of the sample is described in detail by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and fourier transform infrared (FT-IR) studies. The field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) measurements of as-formed samples and samples calcined at 600 °C for 3 h indicate that the as-formed CdSiO3 sample consists of entangled nano-wire bundles with diameters ranging from 20 to 80 nm and lengths in the order of several micrometers. The calcined sample consists of nanobelts of slightly increased diameter and increased length compared to the as-formed samples. The selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) images reflect the polycrystalline nature of nanobelts. The probable mechanism for the formation of nanobelts is also discussed.

Water-evaporation-induced self-assembly of α-MnO2 hierarchical hollow nanospheres and their applications in ammonia gas sensing

In this work, α-MnO2 hierarchical hollow nanospheres with diameters of 1–2.5μm, which are composed of densely aligned nanowires with diameters of 10–15nm and length of about 1μm on the shell, have been prepared via a simple water-evaporation-induced self-assembly (WEISA) route. MnSO4·H2O and (NH4)2S2O8 have been used as raw materials with the presence of Ag+ ions in the reaction system. Experiments reveal that α-MnO2 hierarchical hollow nanospheres derive from solid nanospheres composed of nanowire clusters shortly after evaporation (0.5h) and finally split into randomly dispersed nanowires with longer evaporation time (8h). The process can be explained with Ostwald ripening mechanism. In addition to the evaporation time, the existence of Ag+ ions plays an important role in controlling the phase and morphology of the evaporation product. Furthermore, the ammonia gas sensing properties of the as-prepared samples have been investigated at room temperature with a simply adapted resistance-type gas sensor. The sensors exhibit good sensing performances with quick response and recovery, good repeatability and no need for heat regeneration. The results indicate that the sensor based on α-MnO2 hierarchical hollow nanospheres exhibits higher response to ammonia gas than the one based on α-MnO2 nanowires.

An Alkaline Al–H2O2 Semi‐Fuel Cell Based on a Nickel Foam Supported Co3O4 Nanowire Arrays Cathode

AbstractThe electrode of Co3O4 nanowire arrays directly grown on nickel foam is prepared via a facile one‐step method. The electrode is characterised by scanning and transmission electron microscopy and tested as the cathode of an Al–H2O2 semi‐fuel cell. We found that Co3O4 forms clusters of nanowires with length up to around 15 μm and diameter around 250 nm. The nanowire is composed of interconnected nanoparticles. Effects of H2O2 concentrations, catholyte KOH concentration, catholyte flow rate and operation temperature on the cell performance are investigated. The cell exhibited an open circuit voltage of 1.4 V, and peak power densities of 85 and 137 mW cm–2 at 25 and 65 °C, respectively, while running on 0.4 mol L–1 H2O2 at a flow rate of 80 mL min–1.

Effect of Mn-doping on the growth mechanism and electromagnetic properties of chrysanthemum-like ZnO nanowire clusters

Chrysanthemum-like ZnO nanowire clusters with different Mn-doping concentrations are prepared by a hydrothermal process. The microstructure, morphology and electromagnetic properties are characterized by x-ray diffractometer high-resolution transmission electron microscopy (HRTEM), a field emission environment scanning electron microscope (FEESEM) and a microwave vector network analyser respectively. The experimental results indicate that the as-prepared products are Mn-doped ZnO single crystalline with a hexagonal wurtzite structure, that the growth habit changes due to Mn-doping and that a good magnetic loss property is found in the Mn-doped ZnO products, and the average magnetic loss tangent tanδm is up to 0.170099 for 3% Mn-doping, while the dielectric loss tangent tanδe is weakened, owing to the fact that ions Mn2+ enter the crystal lattice of ZnO.

Study on the annealing-dependent photoluminescence properties of SnO2 cluster-system structures

SnO 2 cluster-system structures were synthesized via a two-step temperature-rising thermal evaporation method with short oxidation time. Field emission scanning electron microscopy, X-ray diffraction and transmission electron microscopy were used to characterize the morphological and structural feature of the product as nanowire cluster and nanoparticle cluster. The photoluminescence spectra exhibit that, as annealing time in air increases, the intensity of the newly found strong ultra-violet emission decreases while the green emission is increased. Raman spectrum and X-ray photoelectron spectroscopy investigations reveal that the relatively decreasing intensity was dominated by the increasing oxygen vacancy. Further calculation based on the SnO 2 crystal lattices with H 2 O molecules at different steps in evaporation process was performed. The result of this calculation confirms that, rather than the influence of H 2 O molecules from air, the decreasing intensity is the result of the combined action of the formation of oxygen vacancy and the energetic oxygen compensation in annealing treatment.

Organization of matter into one-dimensional units on designed media

Abstract The organization of magnetic materials into one-dimensional micro- and nanowires on designed media is discussed, exemplified by two experiments on the microscale and nanoscale, with regard to particles as basic building blocks for the growth and development of matter. In the first organizational experiments, cobalt (Co) micro-particles are assembled on patterned media with perpendicular magnetization by acoustic vibrations onto designed shapes reflecting macroscopically the parent material. In the second experiments, semiconductor Germanium-Dysprosium (Ge98Dy2) matter is assembled on gold (Au) catalytic nuclei in a tube reactor by physical vapor transport as clusters of nanowires. The underlying mechanisms of organization are described, and similarities and distinctive features in the processes are discussed. The role of the energy-input in the form of mechanical vibrations and heat is outlined with its similar impact on the assembly and growth of matter on surfaces. The description of these experiments in view of organization allows more control over the processes of planned arrangement on designed media. Routes for further progress in this direction are briefly outlined.

Nucleation and coalescence effects on the density of self-induced GaN nanowires grown by molecular beam epitaxy

The evolution of the density of self-induced GaN nanowires as a function of the growth time, gallium rate, and growth temperature has been investigated by scanning and transmission electron microscopy. Nucleation and coalescence effects have been disentangled and quantified by distinguishing between single nanowires and nanowire clusters. Owing to the very specific nanowire nucleation mechanism involving a shape transition from spherical-cap-shaped islands, the nanowire density does not follow the standard island nucleation theory. Furthermore, the detrimental nanowire coalescence process can be significantly reduced by raising the growth temperature.

Temperature-Dependent Resistive Switching in Bulk Silver Nanowire−Polystyrene Composites

We describe the temperature-dependent characterization of resistive switching behavior in bulk silver nanowire−polystyrene composites between 10 and 300 K. We propose that the resistive switching behavior is caused by the electroformation of silver filaments between adjacent nanowire clusters, resulting in an extension of the electrical percolation network in the on state. This process is reversible above 200 K, and irreversible below 100 K. The switching fields are shown to depend strongly on sample composition (i.e., proximity to the electrical percolation threshold), as well as measurement temperature.

Resistive Switching in Bulk Silver Nanowire-Polystyrene Composites

Traditionally, bulk nanocomposites of electrically conducting particles and insulating polymers have been categorized as either insulating or conducting when the nanoparticle concentration is below or above the percolation threshold, respectively. Meanwhile, thin-film polymer nanocomposites can exhibit resistive switching behavior appropriate for digital memory applications. Here, we present the first report of reversible resistive switching in bulk, glassy polymer nanocomposites. At compositions close to the electrical percolation threshold measured at low voltage, silver nanowire-polystyrene nanocomposites demonstrate reversible resistive switching with increasing voltage at room temperature. Nanocomposites with compositions outside of this range exhibit either irreversible switching, or no switching at all. We propose that resistive switching in these materials is the result of the field-induced formation of silver filaments that bridge adjacent nanowire clusters, extending the percolation network and decreasing the sample’s bulk resistivity. These findings break from the usual dichotomy of insulating or conducting properties in polymer nanocomposites and could inspire new devices that capitalize on this responsive behavior in these versatile materials.

Spinel LiCo0.7Mn1.3O4 Nanowire Clusters as Electrode Materials

the presence of high-spin Mn 3 + :t2g 3 eg 1 ions—resulting in a huge change of volume and severe fading of the capacity. [7] The power density (rate capability) of these cathode materials with bulk sizes in the micrometer-regime is generally low due to the high level of polarization at high charge–discharge rates (above 2 C). This high polarization is believed to result from slow lithium diffusion or low electrical conductivity in the active material. Therefore, “nanostructuring” was introduced to overcome these shortcomings, through shortening the diffusion paths for mass transport and increasing the surface area for charge transfer. [8–10] In addition, electrode density is considered to be one of the factors that affects the energy density: a higher electrode density leads to a higher energy density. [11] A

Magnetotransport properties of Mn–Si–C based nanostructures

Boron-incorporated Mn5SiC nanowires were grown using chemical vapor deposition method. The nanowire cluster exhibits magnetic hysteresis loops at room temperature and the strength of the magnetic behavior depends on the concentration of the boron incorporation. Mn5SiC nanowire-based devices exhibit spin dependent transport properties which shows significant changes with boron content. Large magnetoresistance is observed in lightly boron-incorporated nanowire devices and it decreases with increase in boron content.

Micro- and nanoparticles of condensed DNA formed in a PCR with yeast genomic DNA as a template. Electron microscopy data

It has been previously found that in a PCR with yeast genomic DNA as a template, microparticles of condensed DNA are formed in the presence of KlenTaq polymerase. In the present work, the study of these microparticles was continued using electron microscopy. It was shown that along with standard electron-dense microspheres, microspheres of a low electron density with a few thorns or without any thorns are formed. Various types of nanoparticles were detected in the samples: nanowires, dot-like electron-absorbing particles (nanodots), and compact nanoparticles (nanoscales) of different shape and size. It was found that increasing the number of PCR cycles above the optimum leads to an abrupt rise in the amount of nanoparticles in the PCR mixture. Suspensions of microparticles after quick (5 min) heating at 94 degrees C were examined. The partial melting of the microspheres in the heated samples was established: they lost part of the DNA and decreased in size; simultaneously, abundant clusters of nanowires appeared. The effect of nuclease S1 on the DNA of microspheres was studied. The molecular mechanisms of the formation of micro- and nanoparticles are discussed.

Rotational Maneuver of Ferromagnetic Nanowires for Cell Manipulation

1-D magnetic nanowires provide a powerful tool for investigating biological systems because such nanomaterials possess unique magnetic properties, which allow effective manipulation of cellular and subcellular objects. In this study, we report the rotational maneuver of ferromagnetic nanowires and their applications in cell manipulation. The rotational maneuver is studied under two different suspension conditions. The rotation of nanowires in the fluid is analyzed using Stokes flow assumption. Experimental results show that when the nanowires develop contacts with the bottom surfaces, the rotational maneuver under a modest external magnetic field can generate rapid lateral motion. The floating nanowires, on the other hand, do not exhibit substantial lateral displacements. Cell manipulation using skeletal myoblasts C2C12 shows that living cells can be manipulated efficiently on the bottom surface by the rotational maneuver of the attached nanowires. We also demonstrate the use of rotational maneuver of nanowires for creating 3-D nanowire clusters and multicellular clusters. This study is expected to add to the knowledge of nanowire-based cell manipulation and contribute to a full spectrum of control strategies for efficient use of nanowires for micro-total-analysis. It may also facilitate mechanobiological studies at cellular level, and provide useful insights for development of 3-D in vivo-like multicellular models for various applications in tissue engineering.