Amorphous Nanowires Research Articles

Growth of SiO2 nanowires co-catalyzed by carbon and nickel particles

By method of the pulsed laser deposition of Ni/C bilayer precursor films and annealing in N2, ambient amorphous SiO2 nanowires were prepared on fused quartz substrates. Field emission scanning electron microscopy images reveal that after annealing at the temperature of 1200°C for 1 h, the Ni/C films turn into dense nanowires with lengths and widths of several micrometers and tens of nanometers, respectively. Results of transmission electron microscopy, high resolution transmission electron microscopy, and energy dispersive X-ray spectroscopy fitted on it show that the nanowires are amorphous SiO2 nanowires and that they are grown in the Ni-leading solid-liquid-solid mechanism. Besides, C particles can promote SiO2 nanowires to grow longer in the forms of carbon and carbon monoxide.

Amorphous Bimetallic Nanowires with High-Performance Microwave Absorption: A Case for FeCo Nanowires

Amorphous FeCo nanowires (NWs) with the average diameter of 120[Formula: see text]nm were successfully prepared with a magnetic-field-assisted (MFA) hydrothermal method. Rapid reaction time was adopted to obtain amorphous FeCo NWs, being checked by XRD and TEM. Tuning the stoichiometric ratio of Fe/Co content meets the optimal impedance matching under different absorption frequency, making both improved intensities and frequency ranges of microwave absorption. For example, under 3[Formula: see text]mm coating thickness, the reflection loss (RL) peaks of Fe3Co7, Fe5Co5 and Fe7Co3 NWs are [Formula: see text]25.88[Formula: see text]dB at 4[Formula: see text]GHz, [Formula: see text]19.06[Formula: see text]dB at 4.24[Formula: see text]GHz and [Formula: see text]21.98[Formula: see text]dB at 5.44[Formula: see text]GHz. The related efficient absorption bandwidths ([Formula: see text]10 dB) of Fe3Co7 NWs, Fe5Co5 NWs and Fe7Co3 NWs are 5.40[Formula: see text]GHz, 3.52[Formula: see text]GHz and 4.91[Formula: see text]GHz, respectively. It is ascribed to integrating enhanced dielectric/conductive losses, negligible damages from eddy current effect and good impedance matching for high-performance FeCo NWs absorbers. This work paves a new path on synthesizing bimetallic wire-like nanostructures for microwave absorption demands.

The Blocking Temperature of an Amorphous Alternate A and B Layers Cylindrical Nanowire

The blocking temperature of an amorphous cylindrical nanowire of length L and radius R is studied within the framework of Monte Carlo simulation based on Metropolis algorithm. The nanowire is formed by alternate layers of atoms A and B. The interlayer coupling JAB is ferromagnetic. The effects of the exchange couplings JB and JAB, the plane anisotropy Dxy, and the amorphization α on the blocking temperature of the system are investigated. We found that the blocking temperature increases with increasing the value of the exchange couplings JB and JAB and decreases with increasing the plane anisotropy Dxy and the degree of the amorphization α.

Propagation of amorphous oxide nanowires via the VLS mechanism: growth kinetics.

This work reports the growth kinetics of amorphous nanowires (NWs) developed by the vapour–liquid–solid (VLS) mechanism. The model presented here incorporates all atomistic processes contributing to the growth of amorphous oxide NWs having diameters in the 5–100 nm range. The steady state growth condition has been described by balancing the key atomistic process steps. It is found that the 2D nano-catalyst liquid and NW solid (L–S) interface plays a central role in the kinetic analysis. The balance between the 2D Si layer crystallization and oxidation rate is quantitatively examined and compared with experimental values. The atomistic process dependencies of the NW growth rate, supersaturation (C/C0), desolvation energy (QD) barrier and NW diameter have been analyzed in detail. The model successfully predicts the reported NW growth rate to be in the range of 1–10 μm s−1. A novel seed/catalyst metal-based synthesis strategy for the preparation of amorphous silica NWs is reported. A nickel thin film on Si is used as a seed metal for the Au assisted VLS growth of silica NWs. The experimental results provide evidence of the creation of SiO under the given conditions followed by Si injection in the Au–Si nano-catalyst solution. The usage of seed metal was observed to reduce the growth temperature compared to the methods reported in the literature and obtain similar growth rates. The technique presented here holds promise for the synthesis of sub-100 nm diameter NWs.

Germanium catalyzed vapor–liquid–solid growth and characterization of amorphous silicon oxide nanotubes: comparison to the growth of its nanowires

One-dimensional (1D) nanostructures were grown with a simple technique using continuous-wave laser vaporization of a Ge target containing 5 at.% Si in high-pressure (up to 0.9 MPa) Ar gas atmosphere. A maximum amount (~ 30% of all products) of 1D nanostructures was obtained at 0.9 MPa and these nanostructures were identified as amorphous silicon oxide (SiOx) nanotubes (NTs) and attached with crystalline Ge-rich NPs with elongated prolate-like or sphere-like shapes at their tips by transmission electron microscopy (TEM), high-angle annular dark-field-scanning TEM, and energy dispersive X-ray line scan spectrometry. As the Ar pressure decreased from 0.9 to 0.03 MPa, the average diameters, wall thicknesses, and lengths of the NTs decreased from 57.9 to 22.9 nm, 13.2 to 6.7 nm, and 2.1 to 0.2 µm, respectively, and the tip NP size decreased from 139.0 to 41.7 nm. There was a strong correlation among the diameters, wall thicknesses, and lengths of the NTs and tip Ge NP sizes, indicating the role of molten Ge NPs as catalyst seeds for the precipitation of SiOx in a vapor–liquid–solid growth mechanism at high temperature. The SiOx precipitation quantities from the seed NPs for the NTs were compared with those of amorphous SiOx nanowires (NWs) at 0.1–0.9 MPa to clarify the growth mechanism of the NTs. We argue that smaller precipitation quantities of SiOx than those for the NWs play a critical role in the formation of cap structures with different sizes and shapes from the molten Ge NPs and the growth of the NTs.

Amorphous iron sulfide nanowires as an efficient adsorbent for toxic dye effluents remediation.

Environmental and health concerns arising from the toxicity of organic dye effluents is still the issue of the twenty-first century. In that regard, this study presents iron sulfide (FeS2) for its use in environmental remediation application. Amorphous phase FeS2 nanowires were synthesized by PVP-assisted solvothermal reaction and were characterized using XRD, XPS, BET, FE-SEM, and EDS techniques. The amorphous phase FeS2 is attractive from material synthesis point of view as its synthesis does not require delicate control over the process parameters, unlike the crystalline phase. The 1-D nanowire FeS2 had a high surface-to-volume ratio with negative zeta potential within a wide pH range. Having those surface and microstructural properties, these nanowires exhibited excellent adsorption property towards model organic dyes, Congo red (anionic), and methylene blue (cationic), with theoretical adsorption capacity of 118.86 and 48.82mgg-1, respectively. Adsorption kinetics and isotherm models were implemented to study the adsorption processes at different adsorption conditions (pH, adsorbent loading, initial adsorbate concentration). The pH dependence of the adsorption and FT-IR analysis evidenced the prevalence of both physisorption and chemisorption during the adsorption of Congo red. Recyclability test proved the excellent performance of this amorphous FeS2 nanowire adsorbent for three consecutive cycles. Considering its ease of synthesis, excellent adsorption property, and cyclic performance, the as-prepared adsorbent could be a promising material for dye effluents treatment.

Athermal coalescence of two parallel and contacting amorphous SiOx nanowires as induced by uniform e-beam irradiation

The coalescence of two parallel and contacting amorphous SiOx nanowires (a-SiOx NWs) as induced by uniform electron beam irradiation was in-situ studied at room temperature in a transmission electron microscope. It was observed that during the irradiation the two parallel and contacting NWs exhibited a rapid athermal coalescence at and near the contacting surface and finally evolved into a single NW with a bigger diameter where atom loss during the coalescence process was not observed. Based on atom diffusion and plastic flow driven by effect of nanocurature of the a-SiOx NWs, and effect of athermal activation induced by the electron beam, a new mechanism was proposed to elucidate the experimental phenomena.

Nickel-carbonate nanowire array: An efficient and durable electrocatalyst for water oxidation under nearly neutral conditions

It is highly attractive but still remains a great challenge to develop an efficient electrocatalyst for oxygen evolution reaction under nearly neutral conditions. In this work, we report the transformation of Ni3S2 nanowire array on nickel foam into the amorphous nickel carbonate nanowire array on nickel foam (NiCO3/NF). The resulting NiCO3/NF shows high electrocatalytic activity towards water oxidation and affords current density of 50 mA∙cm‒2 at overpotential of 395 mV in 1.0 mol∙L‒1 KHCO3. Moreover, this NiCO3/NF is also durable with a long-term electrochemical durability of 60 h. This catalyst electrode achieves a high turnover frequency of 0.21 mol O2∙s‒1 at the overpotential of 500 mV.

Novel amorphous nanowires from solution processed Ge25Se65Sb10 chalcogenide glass

Amorphous nanowires were synthesised from bulk GeSeSb Chalcogenide glass using ethylenediamine/ethanolamine solvent by means of a novel one step method. The synthesized nanowires were characterised by XRD, SEM, XPS, EDS and UV–VIS–NIR spectroscopy. Inspite of having same morphology, it was manifested that the nanowire dimension and bandgap Eg could be tuned with solute concentration which helps for synthesis of chalcogenide glass nanowires with controllable characteristics.

Synthesis of Amorphous InSb Nanowires and a Study of the Effects of Laser Radiation and Thermal Annealing on Nanowire Crystallinity.

Although various synthesis and characterization strategies have been employed for the synthesis of crystalline nanowires, there is very little work done on development of low-dimensional amorphous semiconductors. This paper presents a simple strategy to grow amorphous (a-) nanowires (NWs) in a chemical vapor deposition (CVD) system. The NWs were grown on substrate coated with indium film and the lack of crystallinity in the as-grown stoichiometric NWs was ascertained by Raman spectroscopy and electron transport measurements. A model proposed to explain the amorphous NW growth mechanism takes into account the fact that NW growth was carried out at the high temperature ramp-up rate of 75 C/min. This high rate is believed to affect the growth kinematics and determine the arrangement of atoms in the growing NW. Raman spectrum of the as-grown sample shows a broad peak around 155 cm, indicative of the presence of high density of homopolar - bonds in the amorphous matrix. It was also found that high intensity laser light induces localized crystallization of the NW, most likely due to radiation-stimulated diffusion of defects in a-. The nonlinear trend of the current-voltage characteristics for individually contacted a- NWs was analyzed to prove that the non-linearity is not induced by Schottky contacts. At high bias fields, space charge limited conduction was the proposed electron transport mechanism. Post-growth annealing of the as-grown a- NWs was found to be very effective in causing the NWs to undergo a phase transition from amorphous to crystalline.

Amorphous FeCoPOx nanowires coupled to g-C3N4 nanosheets with enhanced interfacial electronic transfer for boosting photocatalytic hydrogen production

The building of an optimized interface between the cocatalyst and the photoactive materials is significant for understanding the charge transfer mechanism and designing high-performance catalysts at atomic level, however, still a great challenge. Herein, we develop a new method to synthesize a class of hybrid photocatalyst by coupling amorphous FeCoPOxnanowires (FeCoPOx(NWs)) tog-C3N4 photocataysts (denote as FeCoPOx(NWs)-C3N4) for greatly boosting the photocatalytic activity, which shows 3.5-fold higher H2-production activity than the state-of-art crystalline FeCoPOy nanoparticles/g-C3N4 hybrid photocataysts (denote as FeCoPOy(NPs)-C3N4). The structure analysis by X-ray absorption fine structure (XAFS) reveals that the Fe species in FeCoPOx(NWs)-C3N4 owns a lower coordination number than that in FeCoPOy(NPs)-C3N4, which can contribute to the formation of strong interface between FeCoPOx(NWs) and g-C3N4. The first-principles simulation confirms that the amorphous FeCoPOx(NWs) not only can build a stable interface with g-C3N4 by forming more Fe-N bonds, but also own an optimized electronic properties for enhancing electron transfer from g-C3N4 to FeCoPOx(NWs). The strong interfacial electronic effect of FeCoPOx(NWs)-C3N4 contributes to its high H2-production activity.This work not only develops a new method to prepare the high-performance low-cost cocatalyst as Pt alternative for H2 production, but also provide a new insight into optimizing the interface between cocatalyst and photocatalyst for photocatalytic reaction.

Novel bimodal ZnO (amorphous)/ZnO NPs (crystalline) electrospun 1D nanostructure and their optical characteristic

The aim of presented study were to produce amorphous ZnO nanowires filler by crystalline ZnO nanoparticles via the electrospinning process from a polyvinylpyrrolidone (PVP)/zinc nitrate (Zn(NO3)2/dimethylformamide (DMF) and ethanol (EtOH) solution. The as obtained nanofibers were calcined at temperatures ranging from 400 to 600 °C to remove the organic phase. The 1D bimodal ZnO NWs were studied using a scanning and a transmission electron microscope (SEM, TEM) to analyse the morphology and structure of obtained materials. In order to examine the chemical structure of nanowires, the energy dispersive spectrometry (EDX) was used. Besides, a thermogravimetric analysis (TGA) was performed to show the polymer concentration loss in a function of temperature in order to obtain pure zinc oxide nanowires. The optical property analysis was performed on the basis of UV–Vis spectra of absorbance as a function of the wavelength. Using the modified Swanepoel method, which the authors proposed, and the recorded absorbance spectra determined the banded refractive index n, real n' and imaginary k part of the refractive index as a function of the wavelength, complex dielectric permeability ε, real and imaginary part εr and εi of the dielectric permeability as a function of the radiation energy of the produced ZnO nanowires.

Manufacturing process, characterization and optical investigation of amorphous 1D zinc oxide nanostructures

The purpose of this article was to produce amorphous ZnO nanowires via the electrospinning process from a polyvinylpyrrolidone (PVP)/zinc acetate dihydrate (Zn(COOH)2)/dimethylformamide (DMF) and ethanol (EtOH) solution. The as obtained nanofibers were calcined at temperatures ranging from 400 to 600 °C to remove the organic phase. The one-dimensional zinc oxide nanostructures were studied using a scanning electron microscope (SEM) and a transmission electron microscope (TEM) to analyse the influence of the used temperature on the morphology and structures of the obtained ceramic nanomaterials. In order to examine the chemical structure of nanowires, the energy dispersive spectrometry (EDX) was used. Besides, a thermogravimetric analysis (TGA) was performed to show the polymer concentration loss in a function of temperature in order to obtain pure zinc oxide nanowires. The optical property analysis was performed on the basis of UV–vis spectra of absorbance as a function of the wavelength. Using the modified Swanepoel method, which the authors proposed, and the recorded absorbance spectra determined the banded refractive index n, real n′ and imaginary k part of the refractive index as a function of the wavelength, complex dielectric permeability ɛ, real and imaginary part εr and εi of the dielectric permeability as a function of the radiation energy of the produced ZnO nanowires.

Hydrothermal synthesis and characterization of silica nanowires using rice husk ash: an agricultural waste

One-dimensional structures are the smallest dimension structures that represent a unique system for analyzing phenomena at the Nanoscale. Nanowires, which can be used for space confined transport phenomena and enhanced optical properties, are believed to play significant role in the function and integration of Nano electronics and Nano optoelectronics devices. Nanowires with well controlled morphology and extremely high aspect ratio can be obtained by various complex techniques but the demand of upcoming future technology is to synthesize large scale 1D nanostructures with simple and efficient cost effective methods. With this view, in the present study, large scale amorphous silica nanowires (SiO2 NWs) were synthesized from rice husk ash using Fe2O3 assisted hydrothermal method and characterizations of these nanowires along with rice husk ash (RHA) containing porous silica, were done using various techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis spectroscopy and photoluminescence (PL). The structural study of silica nanowires were studied using XRD, indicating the amorphous phases of silica in both RHA as well as nanowires. The chemical composition along with symmetric or anti-symmetric starching bonds of amorphous SiO2 NWs and RHA was confirmed using FTIR. The morphological study was done using SEM and TEM. The SiO2 NWs so obtained have diameter in the range from 15 to 35 nm and length about 0.5 µm. In optical study, the enhanced band gap of amorphous SiO2 NWs as compared to RHA was observed using UV–Vis spectroscopy. PL spectroscopy shows strong blue light emission by silica nanowires as compare to RHA. This study opens up new areas for research to modulate optoelectronic properties of SiO2 nanowires for the novel device application.

Fabrication of amorphous silica nanowires via oxygen plasma treatment of polymers on silicon

We demonstrate a facile non-catalytic method of fabricating silica nanowires at room temperature. Different polymers including photoresists, parylene C and polystyrene are patterned into pedestals on the silicon substrates. The silica nanowires are obtained via the oxygen plasma treatment on those pedestals. Compared to traditional strategies of silica nanowire fabrication, this method is much simpler and low-cost. Through designing the proper initial patterns and plasma process parameters, the method can be used to fabricate various regiment nano-scale silica structure arrays in any laboratory with a regular oxygen-plasma-based cleaner or reactive-ion-etching equipment.

Textural properties determined CO2 capture of tetraethylenepentamine loaded SiO2 nanowires from α-sepiolite

To understand the effect of porous parameters and chemical components on CO2 capturing performance of solid state amine absorbents and their kinetic parameters, a clay mineral-based CO2 absorbent was prepared by impregnating five different liquid amines onto SiO2 nanowire clusters from fibrous sepiolite (Sep). Characterization was conducted by XRD, SEM, FTIR, and N2 adsorption–desorption isotherm, CO2 adsorption performances were measured by TGA. After acid treatment, the raw Sep mineral changed into amorphous silica nanowires, and the largest SBET of the obtained SiO2 nanowires reached 320 m2/g, which was 8 times larger than the pristine mineral. Amongst the adapted amines, tetraethylenepentamine (TEPA) showed superiority in the CO2 adsorption capacity. The optimized adsorption capacity reached 3.7 mmol/g at 75 °C from a CO2 + N2 mixture on a ∼50 wt% TEPA loaded SiO2 sample, and the capacity remained 3.6 mmol/g after ten circles of adsorption/desorption tests. The pore size and pore structure of the matrix, rather than the surface area, will obviously affect the adsorption ability of the product. Kinetic parameters for the CO2 adsorption process fitted well with a fractional-order model, confirming that the CO2 adsorption process by the solid absorbent should be a combination of both physical and chemical reactions. Results in this article provide detailed parameters for preparing and understanding these clay mineral based solid state CO2 absorbents.

Metal passivation effect on focused beam-induced nonuniform structure changes of amorphous SiOx nanowire

In this paper, the passivation effect of Au nanoparticles (AuNPs) on the focused electron beam (e-beam) irradiation-induced nonuniform structure changes of amorphous SiOx nanowire (a-SiOx NW) is in-situ investigated at room temperature in a transmission electron microscope. It is found that the pristine a-SiOx NW demonstrates an accelerated necking at the nanoscale along with a fast, plastic elongation and a local S-type deformation in the axial direction. However, when the surface of a-SiOx NW is modified with uniform AuNPs, it becomes remarkably passivated and the processing transfers from a diffusion (or plastic flow)-dominated status to an evaporation (or ablation)-dominated status. As a result, the necking of the AuNPs-modified a-SiOx NW is greatly retarded with a much lower shrinking rate and there is no visible elongation and bending deformation observed. Further, the combined effects of nanocurvature and beam-induced soft mode and instability of atomic vibration are applied to elucidate the observed new phenomena.

Ni‐Catalyzed Growth of Silica Nanowires From Amorphous Silicon Films and Growth Mechanism

The fabrication of amorphous silica nanowires (NWs) using an amorphous silicon (a‐Si) film grown by plasma‐enhanced chemical vapor deposition is demonstrated. Fabrication is achieved by conventional high‐temperature annealing of an a‐Si layer coated with a thin Ni film. Annealing of the Ni (≈20 nm)/a‐Si (≈1 μm) structure at 1100 °C for 1 h is shown to clearly result in the formation of densely packed amorphous silica NWs with diameters in the range from 35 to 70 nm. A comparison of energy dispersive X‐ray analyses on the tip and body of an NW demonstrates that NW growth proceeded via the solid–liquid–solid mechanism.

Passivation Effect of Gold Nanoparticles on Uniform Beam-Induced Structural Changes of Amorphous SiOx Nanowire

The reshaping of amorphous SiOx nanowires (a-SiOx NWs) as purely induced by uniform electron beam (e-beam) irradiation was in-situ studied at room temperature in transmission electron microscope. It was observed that the axially straight NW kept its perfect straight cylinder-like wire shape and demonstrated a sequential uniform radial shrinkage with the increase of irradiation time. In contrast, the axially curved NW turned straight quickly accompanied with a uniform axial shrinkage and a uniform radial expansion intriguingly. It is expected that such a study especially on the straightening of axially curved NW has important implications for the nanoscale processing and stability of future NW-based structures or devices. More importantly, the findings demonstrate that the traditional knock-on mechanism and electron beam heating effect are inadequate to explain these processes while our proposed nanocurvature effect and energetic beam-induced athermal activation effect obviously dominate the processes.

Electrochemical synthesis of Fe-W and Fe-W-P magnetic amorphous films and Fe-W nanowires

Binary and ternary Fe-W and Fe-W-P films have been obtained electrochemically by using an alkaline stable bath of Fe(III) with a new complexing agent (nitrilotriacetic acid trisodium salt monohydrate-NTA), adequate to avoid carbon incorporation in the deposits and assure the bath durability. The different stages to obtain the alloy deposits through induced co-deposition have been proposed. Significant tungsten percentages in the deposits have been obtained, resulting stable amorphous films with soft-magnetic properties. However, it has been necessary to simplify the deposition process to obtain Fe-W alloy nanowires by means of induced co-deposition in the interior of polycarbonate membranes. For first time, Fe-W magnetic nanowires have been synthesised by templated induced co-deposition.