Porous Wires Research Articles

Controllable Fabrication of Sn/Sb Nanodomains Improved Sb2SnO5 Anodes for Sodium Ion Batteries

AbstractEmbedding the metal phase and modifying the microstructure is an important way to improve the storage capability of Sb2SnO5 (SSO) anodes. Pertaining to sodium‐ion batteries (SIBs), we design and fabricate Sb and Sn embedding porous carbon wires (PCWs) with SSO encapsulated (SSO@Sn/Sb‐PCWs) composite as a high capability anode in this study. Not only accelerate the Na+ ions diffusion, but also augment the stress resistance and the electrochemical reaction reversibility for the multiphase composite. Furthermore, the porous structure finely increases the ions diffusion kinetics, preventing the aggregation of Sn, Sb, and SSO particles, which achieves high reversible capacity while eliminating structure damage. As a consequence, the fabricated SSO@Sn/Sb‐PCWs electrode exhibited exceptional cycling stability, maintaining a high reversible capacity of 448 mAh g−1 after 150 charge/discharge cycles, and good rate capability with current density up to 5.0 A g−1. This new composite material studied in current work could shed light for the creation of sodium ion batteries with high specific energies in the near future.

H2-mediated reduction of GeO2 and chemical vapor deposition of polycrystalline Ge porous films

Hydrogen reduction of metal oxides has received considerable attention owing to no direct emissions of pollutants or greenhouse gasses. In this study, the reduction behavior of GeO2 in H2 flow was investigated in the temperature range 800 K to 1200 K in order to grow Ge films/wires by chemical vapor deposition (CVD) technique at 723 K. A slight oxide reduction was observed at 800 K due to sluggish reaction kinetics. The mass loss from GeO2 increased and exceeded that corresponding to the removal of O2 in GeO2 as the temperature was raised to 1200 K. The excessive loss was attributed to the formation of gaseous GeO species predicted by the thermodynamic calculation. At 900–1000 K, the GeO2 reduction to Ge was nearly complete, close to the thermodynamic prediction. The experimental losses were higher than the predicted ones at 1100 and 1150 K. The discrepancy was explained by a mass-transport theory involving a boundary layer in the gas phase over the powder bed. At 1200 K, the reduction process was close to the equilibrium. It was found that the Ge-containing species in-situ generated by the upstream reaction of GeO2 with H2 at 1100 K and 1200 K sufficed to grow polycrystalline Ge porous films on a Si (400) substrate held downstream at 723 K. Ge wires were also obtained on the Si substrate that was initially covered with an Au film. This exploratory study demonstrates that polycrystalline Ge porous films and wires can be deposited on a Si substrate by CVD technique using environmentally friendly H2 and solid GeO2 precursors.

Synthesis of arrays nanostructured porous silicon wires in electron conductivity type silicon with crystallographic orientation (111)

The method of modified metal-assisted electrochemical etching was proposed and arrays of nanostructured porous silicon wires on n-type monocrystalline silicon substrate with crystallographic orientation (111) were obtained. The influence of the electrolyte composition at the second stage of obtaining on the morphology of silicon wires by scanning electron microscopy methods was revealed. The phase composition of porous silicon wires was controlled by Raman spectroscopy. Keywords: Porous silicon,porous Silicon nanowires, MACE, Nanomaterials, Raman spectroscopy.

Синтез массивов наноструктурированных пористых кремниевых стержней в кремнии электронного типа электропроводности с кристаллографической ориентацией (111)

The method of modified metal-assisted electrochemical etching was proposed and arrays of nanostructured porous silicon wires on n-type monocrystalline silicon substrate with crystallographic orientation (111) were obtained. The influence of the electrolyte composition at the second stage of obtaining on the morphology of silicon wires by scanning electron microscopy methods was revealed. The phase composition of porous silicon wires was controlled by Raman spectroscopy.

Fabrication of a 3D Porous Silver Wire Based on a Template-Assisted Electroless Deposition Method

Porous metal wires are promising in various applications, such as catalysis, energy storage and conversion, electrochemical sensing, and so forth. However, controllable fabrication and structural tuning of porous metal wires remains a daunting challenge. Here, we report the fabrication of 3D porous silver wires based on a template-assisted electroless deposition (ELD) method using an electrospinning-derived elastomer yarn as the template. After the calcination, the elastomer yarn with the deposition of silver nanoparticles can be converted into a 3D porous metallic silver wire with a conductivity higher than 3600 S/cm and a porosity of 86%. The porous structure of the wire could be tuned by changing the repeating cycles of the ELD process for loading silver nanoparticles. More importantly, the electrospinning-based fabrication strategy enables us to incorporate an insulating fibrous layer on the silver wire to impart advanced functionalities. As a proof of concept, a porous silver wire containing a concentric layer of SiO2 microfibers was prepared, and its application as a wire-shaped capacitor for liquid sensing was demonstrated. Benefitting from its completely inorganic nature, high porosity, and chemical stability, the composite wire could sense various organic solvents as well as aqueous solutions with high sensitivity, reliability, and long-term-use stability.

Wires with Continuous Sabal Leaf-Patterned Micropores Constructed by Freeze Printing for a Wearable Sensor Responsible to Multiple Deformations.

The design of porous structure in wearable sensors is very important for the detection of mechanical signals. However, it remains challenging to construct a porous structure capable of detecting all kinds of mechanical signals. Here, round wire with long-range orientated micropores (RW-LOM) is fabricated by a newly established freeze printing technique and constructed into a wearable sensor by the incorporation of carbon nanotubes and polydimethylsiloxane. The Sabal leaf-like lamellar structure in RW-LOM is realized and can be tuned by the proper coordination of slurry concentration and the printing parameters. The fine structures in RW-LOM allow the wearable sensor to detect compression, stretching, twisting, and bending with a high sensitivity, stability, and broad detecting range. This work not only provides a wearable sensor with high stability and high sensitivity but also establishes a technique to construct porous wires that could find applications in the fields like intelligent industry and healthcare.

Alkyl Silica Hybrid Nanowire Assembly in Improved Superhydrophobic Membranes for RO Filtration.

Alkyl silica membranes and wires were synthesized by a sol–gel method, which has the capacity to control the size of the particles or membranes by controlling the reactions. Trimethoxyoctylsilane (C8TMOS) was used as a chemical surfactant; poly(vinylpyrrolidone) (PVP) as an emulsifier, dissolved in butanol for emulsion; and tetraethylorthosilicate (TEOS) as a precursor and a source of silica. An assembly of silica wires was fabricated on glass and cotton substrates by the dip-coating technique. Porous membranes and silica wires were observed using scanning electron microscopy (SEM) images. The contact angles of all of the samples were in the range of 140–154° as measured by ImageJ software, which confirmed the hydrophobic nature of the samples. The contact angle was increased by increasing the amount of the surfactant. Phase changes of silica wires and membranes were investigated by thermogravimetric analysis. Chemical bonds of the sample were studied using Fourier transform infrared (FTIR) spectroscopy. The band gap of silica nanowires was measured to be 3.8–3.4 eV using the UV–visible spectrum and decreased as compared to that of bulk silica. These silica-based porous membranes with enhanced transport properties can be used in filtration and separation techniques. This fabricated hybrid silica membrane showed ∼96% salt rejection within a permeation flux of 3.04 L/m2 h.

Dps protein localization studies in nanostructured silicon matrix by scanning electron microscopy

The present work is related to the microscopic studies of the morphology of the planar and inner part of silicon nanowires arrays before and after immobilization with a natural nanomaterial, Dps protein of bacterial origin. Silicon nanowires were formed by metal-assisted wet chemical etching. To obtain the recombinant protein, Escherichia coli cells were used as excretion strain and purification were carried out using chromatography. The combination of silicon nanowires with protein molecules was carried out by layering at laboratory conditions followed by drying under air. The resulting hybrid material was studied by high-resolution scanning electron microscopy. Studies of the developed surface of the nanowires array were carried out before and after combining with the bioculture. The initial arrays of silicon wireshave a sharp boundaries in the planar part and in the depth of the array, transition layers are not observed. The diameter of the silicon nanowires is about 100 nm, the height is over a micrometer, while the distances between the nanowires are several hundred of nanometers. The pores formed in this way are available for filling with protein during the immobilization of protein.The effectiveness of using the scanning electron microscopy to study the surface morphology of the hybrid material “silicon wires – bacterial protein Dps” has been demonstrated. It is shown that the pores with an extremely developed surface can be combined with a bio-material by deposition deep into cavities. The protein molecules can easily penetrate through whole porous wires matrix array. The obtained results demonstrate the possibility of efficient immobilization of nanoscaled Dps protein molecules into an accessible and controllably developed surface of silicon nanowires.

Optical Properties of Porous Silicon p-Si (100)

In this paper the reflectance spectra and transmission spectra of p-Si (100) porous silicon (PS) and silicon wires in the spectral range of 200 ÷ 1800 nm were investigated. Pore size of PS was 5 μm (lpor Si layer) and 50 μm (lpor Si layer) with porosity of 45 %, 55 % and 65 %. The length of silicon wires varies from 5.5 μm, to 50 μm with a porosity of 60 %. The decrease in the band gap of p-Si (100) porous silicon and silicon wires which grown on both sides of p-Si (100) as compared to the single crystal p-Si (100) is explained by the quantum-sized effect that occurs in the investigated objects.

Spontaneous and Directional Bubble Transport on Porous Copper Wires with Complex Shapes in Aqueous Media.

Manipulation of gas bubble behaviors is crucial for gas bubble-related applications. Generally, the manipulation of gas bubble behaviors generally takes advantage of their buoyancy force. It is very difficult to control the transportation of gas bubbles in a specific direction. Several approaches have been developed to collect and transport bubbles in aqueous media; however, most reliable and effective manipulation of gas bubbles in aqueous media occurs on the interfaces with simple shapes (i.e., cylinder and cone shapes). Reliable strategies for spontaneous and directional transport of gas bubbles on interfaces with complex shapes remain enormously challenging. Herein, a type of 3D gradient porous network was constructed on copper wire interfaces, with rectangle, wave, and helix shapes. The superhydrophobic copper wires were immersed in water, and continuous and stable gas films then formed on the interfaces. With the assistance of the Laplace pressure gradient between two bubbles, gas bubbles (including microscopic gas bubbles) in the aqueous media were subsequently transported, continuously and directionally, on the copper wires with complex shapes. The small gas bubbles always moved to the larger ones.

Porous Gold Nanowires: Plasmonic Response and Surface‐Enhanced Infrared Absorption

Because of its extended surface area porous gold is of potential interest for surface‐enhanced spectroscopy methods. Optical properties of porous and smooth gold nanowires of similar diameter are analyzed with infrared spectroscopy and modeled with finite‐difference time‐domain simulations. By electrochemical deposition in ion‐track etched polymer smooth gold and gold–silver alloy nanowires are synthesized. Porous gold nanowires are subsequently obtained by dealloying. The porosity clearly affects important plasmonic characteristics, resulting in a strong redshift of the resonant wavelength, and significant line broadening, which can be convincingly explained by effective Drude parameters related to a lowered average electron density and a higher electron scattering in the porous gold, respectively. Finally, the sensing performance of porous wires is tested by surface‐enhanced infrared absorption. The measurements show a similar vibrational signal contrast for smooth and porous wires. This is explained by simulations which reveal that the nanowire near‐field modeled with bulk gold data is higher and thus accordingly the vibrational signal is enhanced compared to nanowires modeled with the effective Drude parameters of porous gold. This means that the advantages offered by the larger surface of porous wires are counterbalanced by lower near‐field strength.

Fabrication And Plasmonic Characterization Of Au Nanowires With Controlled Surface Morphology

Gold nanowires are attracting great attention due to their ability to sustain surface plasmons and are thus promising candidates for sensing applications such as surface enhanced Raman and infrared spectroscopy. Controlling all nanowire parameters is crucial to adjust the resonance wavelengths and to obtain high electric field enhancements. We have fabricated Au nanowires with controlled dimensions and surface morphology by electro-deposition of Au and Au-Ag nanowires in the pores of ion-tracketched polymer templates. Smooth and rough nanowires are fabricated by the use of different polymer types. By dealloying of Au-Ag wires, porous Au wires are being created. In addition, we have analyzed the surface plasmonic properties of smooth and porous Au nanowires by scanning transmission electron microscopy combined with electron energy-loss spectroscopy. Our results reveal the excitation of five different longitudinal modes in the smooth as well as in the porous Au wire. The resonance energies of the porous wire are red-shifted compared to the energies of a smooth Au wire with same dimensions, which demonstrates that the surface morphology of the nanowire is an important parameter to tune the multipole surface plasmon modes to specific energies. Knowledge on the plasmonic properties of nanowires dependent on their surface morphology is indispensable for their efficient application for sensor technology. Copyright © 2015 VBRI press.

Nanostructured porous wires of iron cobaltite: novel positive electrode for high-performance hybrid energy storage devices

Nanostructured porous wires of FeCo2O4supported on nickel foam were synthesized and employed as binder/additive-free electrodes in asymmetric aqueous supercapacitors, showing a high energy density of 23 Wh kg−1.

Hierarchical Macro‐mesoporous Pt Deposits on Gold Microwires for Efficient Methanol Oxidation

AbstractHierarchically ordered macro‐mesoporous Pt films have been synthesized on gold microwires by filling the void space of a colloidal crystal template with mesoporous Pt through electrodepositing the metal in the presence of self‐assembled surfactant molecules, followed by a dissolution of the template. The network of interconnected macro‐ and mesopores in the homogeneous films was characterized using microscopy (SEM, TEM) and electrochemical techniques. The active surface areas of the porous wires increased by more than three orders of magnitude compared to nonporous samples. These high surface‐to‐volume ratios resulted in a high electrocatalytic activity for methanol oxidation.

Hydrogen template assisted electrodeposition of sub-micrometer wires composing honeycomb-like porous Pb films

High surface area porous Pb films are electrodeposited using a hydrogen bubble dynamic template. The influence of the experimental parameters on the morphology features such as the pore size, wall thickness, and sub-micrometer size features is investigated. Two structural transformations between sub-micrometer wires and particles obtained by adjusting the HClO4 concentration are observed. At a low HClO4 concentration, the growth of sub-micrometer wires is favored. The deposition of particles or wires covered by particles is observed at higher H+ concentrations. The addition of sodium citrate as an additive facilitates the preservation of Pb in the form of wires. Adjusting the concentration of Pb(ClO4)2·3H2O influences the mass transfer of Pb and affects its morphology. At low concentrations, the deposition of porous Pb films composed of porous wires is shown. The additional deposition of particles on wires is observed at high concentrations. The formation process of honeycomb-like porous structures is revealed by analysis of films deposited during different deposition time. The influence of the current density on the micro and sub-micrometer scale morphologies is presented.

Biopolymer Networks for the Solid‐State Production of Porous Magnetic Beads and Wires

AbstractAqueous solutions of sodium carboxymethyl cellulose are used for the morphosynthesis of spherical and wire‐shaped biopolymer networks, in which Fe3+ cations serve as a crosslinking and hardening agent. Their morphology remains intact upon drying, resulting in monolithic beads (1 mm) and wires (ca. 80 μm), which are exploited as reaction vessels to pre‐encapsulate poly(ethylene glycol) 400 (PEG 400) and cobalt cations. A solid‐state reaction in an inert atmosphere at 600 °C affords porous carbonaceous xerogels, macroscopically shaped as beads or wires and decorated with nanocrystalline magnetic iron oxide, metallic iron, or iron–cobalt alloy particles, thus imparting magnetic properties to the products. As such the reduction of Fe3+ species to α‐Fe nanoparticles can be achieved without H2 treatment, since poly(ethylene glycol) serves as a reducing agent and the encapsulated Co2+ aids in the subsequent growth of the metallic iron particles. Particularly interesting are the magnetic properties of the carbon–α‐Fe composite, in which the size of the magnetic particles, estimated near the boundaries of the single magnetic domain, gives rise to increased coercivity compared with that of bulk iron.

Synthesis of porous wires from directed assemblies of nanospheres.

A method is reported for the fabrication of wires with extended pore structures. Nanospheres are initially infiltrated into the one-dimensional channels of alumina or polymer porous membranes. Metal is then electrochemically deposited within the channels. Removal of the membrane and nanospheres results in porous wires. The production of 1-mum diameter wires with 300- or 500-nm diameter pores and 300-nm diameter wires with 140-nm pores illustrates the utility of this approach. Contacts between the spheres and the channel wall result in openings on the surface of the wires, and contacts between the spheres themselves produce openings between adjacent pores. Some short-range ordering of the spheres within the channels, as reflected in the wire pore structure, is evident. Characterization of the porous wires by electron microscopy is presented, and the potential applications of materials is discussed.

Identity of the light-emitting states in porous silicon wires

We present empirical pseudopotential calculations of the electronic structure of [001] silicon quantum wires, aiming at identification of the states that couple radiatively to the valence-band maximum. We find that the near-gap wave functions differ qualitatively from effective-mass depictions. Instead, they can be described as off-Γ bulk states. The effects of H chemisorption on the wire energies and wave functions are studied. We find that the Si skeleton dominates the emission. The resulting lifetimes versus energy relation agrees with the experimental measurements only if one assumes coexistence of quantum wires with quantum dots.