Morphology Of Nanowires Research Articles

Highly improved toluene gas-sensing performance of mesoporous Co3O4 nanowires and physical mechanism

Mesoporous Co3O4 nanowires were synthesized with the nanocasting method, and then the dispersed Co3O4 nanowires (Co3O4-DNWs) were separated from the bundled Co3O4 nanowires (Co3O4-BNWs) by the centrifugation technique. From the characterization with TEM, X-ray diffraction, UV–vis spectra and nitrogen adsorption-desorption isotherm, both samples present the same mesoporous-structure, diameter and the similar defects due to the same synthesis conditions. All results indicate that the microstructures and morphology of Co3O4 nanowires greatly affect the toluene gas sensing performance. Owing to the mesoporous-structures with the high surface area, the sensitivities of both samples are higher than others’. Co3O4-DNWs exhibit the higher specific surface area (44.98 m2g−1) than Co3O4-BNWs, leading to the excellent gas-sensing properties to toluene gas at the optimized operating temperature of 210℃. Moreover, both samples present the excellent stability and selectivity to toluene gas. The gas-sensing mechanism results from the surface oxygen and toluene gas adsorption through comparing the sensitivity of Co3O4-DNWs and Co3O4-BNWs.

Fabrication of platinum nanowires by centrifugal electrospinning method for proton exchange membrane fuel cell

The centrifugal electrospinning method is employed to fabricate platinum (Pt) nanowires and its application for proton exchange membrane fuel cell (PEMFC) is evaluated. The nanowires are produced from a polymer solution containing hexachloroplatinic acid hydrate as Pt precursor and polyvinyl pyrrolidone (PVP). The effects of system parameters on the morphology of Pt nanowires are studied including the PVP concentration, rotation speed of spinneret, and applied electric field. The electrochemically active surface area (ESA) of the Pt nanowires is characterized by cyclic voltammetry tests. The produced Pt nanowires are also used as electrocatalysts in the cathode of PEMFC and the cell performance is tested. Results show the centrifugal electrospinning method can successfully produce Pt nanowires with mean diameter of 54 ± 14 nm and ESA of 5.64m2g-1, which are comparable to those of traditional electrospun Pt nanowires. The production rate of Pt nanowires can be improved greatly in comparison with the conventional electrospinning technique. It is also found that by the accelerated degradation tests, Pt nanowires demonstrate better durability than commercial Pt/C and the employment of Pt nanowires as electrocatalysts mixed with Pt/C can enhance the fuel cell performance. The present results reveal the centrifugal electrospinning method is an efficient approach to fabricate Pt nanowires for the application in PEMFCs. Novelty statement A centrifugal electrospinning device was designed to fabricate Pt nanowires successfully with good morphology. The production rate of Pt nanowires is enhanced greatly in comparison with the conventional electrospinning method. Electrocatalysts composed of the produced Pt nanowires and Pt/C is found to be able to improve the performance of PEMFC.

Simulation of optical absorption in conical nanowires.

The optical absorptance from arrays of GaAs nanowires (NWs) was examined by the finite element method. Absorptance in cylindrical NWs, frustum nanocones (with base wider than the top) and inverted frustum nanocones (with top wider than the base) was compared. The introduction of higher order HE1n modes, the red-shift of the HE1n modes along the NW length due to NW tapering, and the red-shift of the modes due to increase of the overall NW diameter all contribute to a broadening of the absorption spectrum in conical NWs as compared to NWs with a constant diameter. The optical reflectance versus NW top diameter shows a minimum due to a balance between reflectance from the top of the NWs and reflectance from the substrate between NWs. The optimum geometry for photovoltaic energy conversion was determined from the total photocurrent. An optimum photocurrent of 26.5 mAcm-2 was obtained, corresponding to a conical NW morphology with base diameter of 200 nm, top diameter of 110 nm, and length of 2000 nm. An optimized inverse tapered conical morphology gave comparable performance.

Glucose biosensor electrode fabrication based on CuO /ZnO nanostructures

Zinc oxide nanowires (ZnO NWs) were successfully synthesized by Zn-metal evaporation and deposition of a thin metal film about 20 µm on quartz substrates. Followed by the subsequent oxidation process in the air at 550 oC for 4h. Copper oxide nanoparticles (CuO NPs) were then deposited on ZnO NWs, using the drop-casting technique. The crystal structure and morphology of ZnO nanowires were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results of XRD confirmed that the ZnO has the Wurtizite polycrystalline structure along [101] direction. The SEM images revealed that the highest density of ZnO nanowires was distributed over a large area of the substrate with many wrinkles. The current response to glucose of the CuO/ZnO/Qz electrode gives a linear dependence range from 50 µM to 500 µM of glucose. The typical sample of CuO/ZnO NWs was used for a glucose biosensor electrode. It was found that CuO NPs layer on ZnO NWs has well improved the performance of the electrode and increased the electrocatalytic ability towards glucose oxidation.

Surface characterization and resistance changes of silver-nanowire networks upon atmospheric plasma treatment

Highly conductive silver-nanowire (Ag-NW) networks are used in composite materials as conductive channels. Their resistance tuning can be accomplished by changing the Ag-NW concentration, and, therefore, changing the network structure. In this study, an alternative pathway to resistance engineering of conductive Ag-NW networks by local atmospheric plasma treatment is employed. The corresponding changes in nanowire network morphology and crystallinity as a function of plasma etching time are investigated by time-resolved grazing-incidence X-ray scattering, field-effect scanning electron microscopy, and X-ray photoelectron spectroscopy. Three characteristic etching phases are identified. The first two phases enable the controlled engineering of the electrical properties with different rates of resistance change, which results from changes in nanowire shape, network morphology, and different oxidation rates. Phase III is characterized by pronounced fragmentation and destruction of the Ag-NW networks. These results show the feasibility of atmospheric plasma treatments to tune the local electrical properties of conductive Ag-NW networks. Furthermore, we present a physical Monte Carlo model explaining the electrical network properties as a function of plasma etching time based on the network connectivity and a constant plasma etching rate of 570 ng s−1 cm−2.

Ultrafast Synthesis of Wavy Gold‐Silver Alloy Nanowires with Tunable Diameters in the Range of 2‐10 nm via a Seed‐Mediated Co‐Reduction

AbstractWe report an ultrafast synthesis of wavy gold‐silver (AuAg) nanowires with tunable diameters via a seed‐mediated co‐reduction. The success of current strategy relies on the use of an elevated reaction temperature to accelerate the synthesis to be completed within several minutes and the use of Au seeds with controlled sizes to enable the manipulation over their diameters in the range of 2–10 nm. The presence of chloride‐contained quaternary ammonium surfactant and excessive reductant have been demonstrated to be critical for the high‐yield formation of AuAg products with the unique morphology of wavy nanowire. Due to the advantage in size control, the size effect on the plasmonic behavior of AuAg alloy wavy nanowires is investigated, where the products with sub‐5 nm diameter exhibit a broad shoulder absorbance peak in their spectrum.

Morphology of Ga2O3 Nanowires and Their Sensitivity to Volatile Organic Compounds

Gas sensitive structures made of nanowires exhibit extremally large specific surface area, and a great number of chemically active centres that can react with the ambient atmosphere. This makes the use of nanomaterials promising for super sensitive gas sensor applications. Monoclinic β-Ga2O3 nanowires (NWs) were synthesized from metallic gallium at atmospheric pressure in the presence of nitrogen and water vapor. The nanowires were grown directly on interdigitated gold electrodes screen printed on Al2O3 substrates, which constituted the gas sensor structure. The observations made with transmission electron microscope (TEM) have shown that the nanowires are monocrystalline and their diameters vary from 80 to 300 nm with the average value of approximately 170 nm. Au droplets were found to be anchored at the tips of the nanowires which may indicate that the nanowires followed the Vapor–Liquid–Solid (VLS) mechanism of growth. The conductivity of β-Ga2O3 NWs increases in the presence of volatile organic compounds (VOC) even in the temperature below 600 °C. The gas sensor based on the synthesized β-Ga2O3 NWs shows peak sensitivity to 100 ppm of ethanol of 75.1 at 760 °C, while peak sensitivity to 100 ppm of acetone is 27.5 at 690 °C.

Synthesis of MoTe2 nanowire as an efficient hydrogen evolution reaction material

Ultrathin MoTe2 nanowire was directly synthesized from a mesoporous silica SBA-15 template via nanocasting strategy. The TEM and SEM observations reveal that the as-synthesized MoTe2 has a nanowire morphology with a diameter of 5–6 nm. UV–Vis absorption spectrum shows that there is a broad absorption in the near ultraviolet and visible light range. The bandgap Eg of the monolayered MoTe2 nanowire has been deduced to 1.60 eV, which demonstrates that it is a potential visible-light active material. The electrochemical test shows that MoTe2 nanowire presents a smaller overpotential of 0.41 V at 10 mA/cm2. The Tafel slope of the material is only 58 mV/dec, which is one of the best values for TMD materials without noble metal doping.

Highly selective H2S gas sensor based on WO3-coated SnO2 nanowires

The enhancement of the H2S gas-sensing performance of SnO2 nanowires is vital for practical application. In this study, H2S gas sensors based on WO3-coated SnO2 nanowires were fabricated through a two-step process, namely, the chemical vapor deposition of SnO2 nanowires and then coating with WO3 by sputtering method. The morphology and crystal structures of the SnO2 nanowires coated with WO3 were investigated by field-emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The H2S gas-sensing properties of the fabricated sensors were tested at temperatures of 150–250 °C. The SnO2 nanowires coated with 5 nm WO3 showed the best response to low-concentration H2S gas (0.1–1 ppm). At the optimal working temperature of 200 °C, the sensor had a sensitivity of 177 toward 1 ppm H2S with good selectivity over the contamination of NO2, NH3, H2, and CO gases. We also discussed the gas-sensing mechanism of the fabricated sensor based on the n–n heterojunction between n-type SnO2 and n-type WO3, which formed a thick depletion layer and thus enhanced the sensitivity to H2S.

PREPARATION AND CHARACTERIZATION OF VISIBLE-LIGHT-DRIVEN Ce-DOPED CdS NANOWIRES FOR PHOTODEGRADATION OF RHODAMINE B

Visible-light-driven Ce-doped CdS nanowires were synthesized by a solvothermal method. Phase and morphology of Ce-doped CdS nanowires were investigated by XRD and SEM analyses. The analytical results certified that both CdS and Ce-doped CdS samples were uniform pure phase of hexagonal CdS nanowires. The photocatalytic activities of CdS and Ce-doped CdS nanowires were investigated through the photodegradation of rhodamine B (RhB) under visible light irradiation. The 3% Ce-doped CdS nanowires have the highest photocatalytic efficiency of 95.75% within 120 min and are the promising material used for wastewater treatment.

Theoretical and experimental investigations of Co-Cu bimetallic alloys-incorporated carbon nanowires as an efficient bi-functional electrocatalyst for water splitting

Application of noble metal-free electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) during electrocatalytic water splitting is crucial for clean energy conversion and has drawn extensive attention. However, the development of highly active and low cost electrocatalysts is a considerable challenge. Herein, Co-Cu alloy nanoparticles-incorporated carbon nanowires electrocatalyst was synthesized and evaluated for both OER and HER. The nanomaterials were fabricated by facile electrospinning of sol-gel composed of cobalt acetate, copper acetate, and poly(vinyl alcohol) followed by calcination in an inert environment. Adjusting the composition of the metallic counterpart was found to significantly enhance electrochemical properties of the catalyst. Furthermore, the unique nanowire morphology and structural properties of incorporated Co-Cu alloy, the (Co0.95Cu0.05@CNWs) composition exhibits good electrocatalytic performance for both OER and HER in the alkaline medium. Physicochemical characterizations using X-ray diffraction, X-ray photoelectron spectroscope, scanning electron microscopy, and transmission electron microscopy have confirmed the formation of alloy structure and nanowire morphology. The optimum composition (Co0.95Cu0.05@CNWs) requires small overpotential, ɳ10 of ∼285 mV for oxygen evolution reaction (OER) and ∼160 mV for hydrogen evolution reaction (HER) with the corresponding Tafel slope of 92 mV dec−1 and 172 mV dec−1 versus the reversible hydrogen electrode, respectively. In addition, only negligible loss in activity was observed after 1000 cycles and prodeces cell voltage of 1.58 V at current of 10 mA/cm2 and 1.72 V at current density of 50 mA/cm2 in two electrode system. Density Functional Theory (DFT) calculations were employed to verify experimental results. Electronic density of states (DOS) results reveal an increase in electronic states near the Fermi level upon Co-Cu heterojunctioning with CNWs. This is indicative of improved catalytic activity and more favorable binding energies of HER and OER intermediates. Reaction coordinate diagrams for HER and OER were developed, which aided in identifying thermodynamically limiting steps. This work may provide a feasible approach for incorporating other transition metals to design low-cost and high-performance bifunctional electrocatalysts for overall water splitting.

Influence of sub-10 nm anodic alumina nanowire morphology formed by two-step anodizing aluminum on water wettability and slipping behavior

The influence of the nanomorphology of alumina nanowires (ANWs) fabricated by a two-step anodizing process on the superhydrophobicity was investigated through advancing contact angle (ACA) and receding contact angle (RCA) measurements. Aluminum nanobowl specimens were anodized in pyrophosphoric acid to fabricate an ordered ANW structure with an average diameter of 7.1 nm, and the outermost surface of the ANWs was chemically bonded with fluorinated self-assembled monolayers. The growing ANWs bent immediately their own weight, and pyramidal ANW structures were formed as they joined the surrounding nanowires together. The ACA value increased with the number density of pyramidal ANW structures due to the reducing area fraction of ANWs, and an increased superhydrophobicity with a contact angle of approximately 165° was measured on the low-density pyramidal structure with a density of 8.1 × 1011 m−2. Additional anodizing led to complete nanowire bending; thus, the advancing contact angle decreased. The pyramidal nanowire structure exhibited a large slipping property with a contact angle hysteresis (CAH) < 10°, whereas the bent nanowire structure exhibited a decreased slipping property with a CAH > 100°. Superhydrophobic surfaces with opposite water slipping properties were demonstrated by a water dropping experiment.

Template-less Synthesis of Coded Au Nanowires.

Morphological coding of nanostructures represents a capability in rapid modulation of structural features and most importantly, the transcription of information into nanoscale. Exploiting the regioselectivity in the template-less electrochemical synthesis of ultrathin Au nanowires, we show that rapid alternation of applied potential would cause corresponding change in the width of the emerging nanowire segments. By understanding the growth kinetics, a strong correlation between the nanowire morphologies and the deposition potential is established and applied in emulating the Morse code.

Self-Catalyzed InSb/InAs Quantum Dot Nanowires.

The nanowire platform offers great opportunities for improving the quality and range of applications of semiconductor quantum wells and dots. Here, we present the self-catalyzed growth of InAs/InSb/InAs axial heterostructured nanowires with a single defect-free InSb quantum dot, on Si substrates, by chemical beam epitaxy. A systematic variation of the growth parameters for the InAs top segment has been investigated and the resulting nanowire morphology analyzed. We found that the growth temperature strongly influences the axial and radial growth rates of the top InAs segment. As a consequence, we can reduce the InAs shell thickness around the InSb quantum dot by increasing the InAs growth temperature. Moreover, we observed that both axial and radial growth rates are enhanced by the As line pressure as long as the In droplet on the top of the nanowire is preserved. Finally, the time evolution of the diameter along the entire length of the nanowires allowed us to understand that there are two In diffusion paths contributing to the radial InAs growth and that the interplay of these two mechanisms together with the total length of the nanowires determine the final shape of the nanowires. This study provides insights in understanding the growth mechanisms of self-catalyzed InSb/InAs quantum dot nanowires, and our results can be extended also to the growth of other self-catalyzed heterostructured nanowires, providing useful guidelines for the realization of quantum structures with the desired morphology and properties.

Cu(In,Ga)S2 nanowire arrays: Self-templated synthesis and application for photoelectrochemical water splitting

Polycrystalline Cu(In,Ga)S2 (CIGS) nanowire arrays (NWAs) are synthesized for the first time via a solvothermal method using Cu2S NWAs as self-sacrificial templates. The average diameter and length of the as-synthesized CIGS nanowires are 350 nm and 5 μm, respectively. Based on the experimental results, a novel cation-exchange growth mechanism is proposed. The In3+ and Ga3+ ions diffuse inward while the Cu+ ions outward during the solvothermal reaction, resulting in the formation of CIGS with keeping the original nanowire morphology. We have also investigated the photoelectrochemical performance of CIGS NWAs compared with the pristine Cu2S templates. The photocurrent density and optimal incident photon to current efficiency of CIGS NWAs are 0.39 mA cm−2 and 6% at 450 nm, respectively, which are much higher than those of the Cu2S templates. The reported method will lay a foundation for the synthesis of other multi-compound (ternary and above) metal chalcogenides for PEC applications.

Self‐Poled Sausage‐Like PVDF Nanowires Produced by Confined Phase Inversion as Novel Piezoelectric Nanogenerators

AbstractPiezoelectric poly(vinylidene fluoride) (PVDF) nanowires are of particular interest for energy harvesting as they are ultra‐sensitive to small vibrations. Here, a new, cost‐effective, and scalable approach to producing PVDF nanowires with strongly enhanced power output is presented. The method combines template‐wetting in cylindrical nano‐confinement with anisotropic solvent‐nonsolvent phase inversion to yield a fully novel nanowire morphology consisting of “sausage‐like” strings of nano‐domains. Dynamic numerical simulations of the phase inversion reveal the formation of these structures to be subject to a very rich and complex phenomenology. The simulated dependence of the feature size on the degree of confinement agrees with the experimentally observed trend. It is unambiguously demonstrated that the sausage‐like nano‐generators upsurge the power density to 280% compared to normal nanowires. Finite element modeling explains how the higher deformability of the sausage‐like nanostructures gives rise to this significant enhancement in piezoelectric performance.

Application of two morphologies of Mn2O3 for efficient catalytic ortho-methylation of 4-chlorophenol.

Vapor phase ortho-methylation of 4-chlorophenol with methanol was studied over Mn2O3 catalyst with two kinds of morphologies. Here, Mn2O3 was prepared by a precipitation and hydrothermal method, and showed the morphology of nanoparticles and nanowires, respectively. XRD characterization and BET results showed that, with the increase of calcination temperature, Mn2O3 had a higher crystallinity and a smaller specific surface area. N2 adsorption/desorption and TPD measurements indicated that Mn2O3 nanowires possessed larger external surface areas and more abundant acid and base sites. Simultaneously, in the fixed bed reactor, methanol was used as the methylation reagent for the ortho-methylation reaction of 4-chlorophenol. XRD, XPS, TG-MS and other characterizations made it clear that methanol reduced 4-chlorophenol and its methide, which were the main side-reactions. And Mn3+ was reduced to Mn2+ under the reaction conditions. Changing the carrier gas N2 to a H2/Ar mixture further verified that the hydrogen generated by the decomposition of methanol was not the reason for dechlorination of 4-chlorophenol compounds. Here we summarized the progress of 4-chlorophenol methylation based on the methylation of phenol. Also, we proposed a mechanism of the 4-chlorophenol dechlorination effect which was similar to the Meerwein–Ponndorf–Verley-type (MPV) reaction. The crystal phase and carbon deposition were investigated in different reaction periods by XRD and TG-DTA. The reaction conditions for the two kinds of morphologies of the Mn2O3 catalyst such as calcination temperature, reaction temperature, phenol–methanol ratio and reaction space velocity were optimized.

Controllable preparation of (200) facets preferential oriented silver nanowires for non-invasive detection of glucose in human sweat

(200) facets preferential oriented Ag nanowires were controllably prepared by a simple modified one-step polyol method, in which Cl ions and polyvinyl pyrrolidone (PVP) were employed as nucleating agent and crystal plane inducer, respectively. The evolution in morphology and structure of Ag nanowires were systematically studied by field emission scanning electron microcopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), from which the optimum synthesis conditions for (200) preferentially oriented Ag nanowires were obtained. Based on further electrochemical studies including cyclic voltammetry (CVs) and amperometry analyses, it is interesting found that the enrichment of (200) facets in the Ag nanowires display higher electrocatalytic activity than those of (111) facets towards glucose oxidation. This is attributed that dominant activity (200) facets of Ag nanowires have relatively higher surface energy and stronger adsorption capacity for glucose molecules, which can provide better electrocatalytic performance. The non-enzymatic glucose sensor based (200) facets preferential oriented Ag nanowires exhibits wide linear range of 0.5–3442 ​μM, low detection limit of 0.5 ​μM, and sensitivity is estimated to be 3246.74 ​μA ​cm−2 ​mM−1. Furthermore, the Ag nanowires based non-enzymatic sensor was successfully used for non-invasive detection of glucose in sweat with high accuracy.

Synthesis of cobalt nanowires with high shape anisotropy and crystallinity

Owning the high spontaneous magntization Ms, the Cobalt (Co) is known as one of the important 3d-transition metal elements used for developing soft magnetic materials. With the high value of Ms, Co should become an ideal hard magnetic material if it can be prepared in the form with a large shape anisotropy. This paper presents the results of synthesizing Co nanowires by reducting the carboxylate Co(II) precursor in the presence of RuCl3 functioned as a catalyst via the change of time in the solvothermal chemical process. The structure, morphology, and properties of the obtained Co nanowires were characterized by the X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM). The results revealed the great impacts of the solventhermal’s times and the reaction temperatures on the morphology and nucleations of Co nanowires. The prepared Co nanowires were well crystallized in the hexagonal close-packed (hcp) phase. The highest Ms value of prepared Co nanowires reached 166.9 emu/g by synthesizing at 225 oC for 20 hours. At 175 oC and for 20 hours, the prepared Co nanowire owns the best hard-magnetic performance characterized by the values of 164.3 emu/g and 2.97 kOe for Ms and iHc, respectively. With these results, in the next stage, the synthesized Co nanowires will be used in manufacturing free rare-earth permanent magnets. Keywords: cobalt nanowire, solvothermal, anisotropic shape, magnetic materials.

Highly Doped Si Single Crystal Nanowires via Metallic Flux Nanonucleation

Ever since the advent of scalable production of nanodevices, the search for optimal fabrication techniques of low dimensional materials has gained the attention of scientists and engineers all over the world. In particular, the fabrication of silicon nanowires is being increasingly investigated, due to their potential integration into novel technologies such as biological and optical sensors, solar cells, power generators, and transistors, among others. In this context, this work reports the single-step fabrication of Ga-doped Si bulk and nanowire single crystals. They were obtained through the Metallic Flux Nanonucleation (MFNN) technique, where a nanoporous alumina template was employed to define the nanowire morphology, while Ga was used as flux to both lower the Si melting point and dope the crystals. Our results show that Ga-doped silicon bulk crystals were successfully fabricated via MFNN. The carrier concentration was determined by probing the Hall effect and was found to be (2.5 ± 0.2) x 1019 cm−3. Silicon nanowires were simultaneously obtained, presenting an average wire diameter of 125 ± 26 nm and length up to several tens of microns. These results open the possibility to easily fabricate heavily doped intermetallic cylindrical nanowires, with versatility both on the nanowire composition and the doping element.