Average Diameter Of Nanowires Research Articles

Superhydrophilic PVDF nanofibrous membranes with hierarchical structure based on solution blow spinning for oil-water separation

Nanofibrous membranes (NFMs) are frequently used in oil-water separation thanks to their high porosity, controllable pore size, and convenience in modification to obtain super wettability. However, the low production rate and dense structure of NFMs have limited the industrial applications. In this work, zinc oxide (ZnO) seed loaded polyvinylidene fluoride (PVDF) NFMs with fluffy structure were prepared through solution blow spinning (SBS). Subsequently, ZnO nanowires (NWs) were synthesized based on the seeds through ultrasonic assisted hydrothermal reaction, constructing superhydrophilic surface with hierarchical structure. The u-ZnO-NWs/PVDF showed uniform morphology throughout the entire membrane with an average fiber diameter of 517.35 ± 158.72 nm and an average nanowire diameter of 72.55 ± 20.52 nm, which resulted in a low average pore size (4024.68 ± 393.40 nm), superhydrophilicity, and underwater oleophobicity. The nanowire equipped membrane revealed super high water flux (12960.77 ± 325.04 L·m−2·h−1·bar−1), which could be applied in the separation of oil-in-water emulsions with high separation efficiency (>97 %) and high flux (about 8000 L·m−2·h−1·bar−1) under gravity. Results indicated the potential of SBS u-ZnO-NWs/PVDF in the fields of oil-water separation, sewage treatment, as well as catalytic degradation.

Improving the photoelectrical characteristics of self-powered p-GaN film/n-ZnO nanowires heterojunction ultraviolet photodetectors through gallium and indium co-doping

ZnO, Ga-doped ZnO (GZO), In-doped ZnO (IZO), and Ga–In co-doped ZnO (GIZO) nanowire arrays were grown on a template of sapphire/p-GaN thin film by low-temperature hydrothermal method for fabricating self-powered p-GaN/n-ZnO heterojunction ultraviolet (UV) photodetectors. The authors investigated the effects of Ga or In single doping and Ga–In co-doping on the microstructural features and optical properties of hydrothermally synthesized ZnO nanowires and conducted a comparison study on the photosensing characteristics and photoelectrical response performances of four kinds of p-n heterojunction UV photodetectors. X-ray diffraction (XRD) examination showed that the as-synthesized ZnO-based nanowire arrays had a single-phase hexagonal wurtzite structure and exhibited a preferential orientation along the (002) plane. Scanning electron microscope (SEM) observation evidenced that the type of dopants modified the morphology and average diameter of the nanowires. The average diameter of ZnO-based nanowires was in the range of 61–101 nm. Room-temperature photoluminescence (PL) spectra revealed that these as-synthesized ZnO-based nanowires had high crystalline quality. The current-voltage (I–V) curves of heterojunction photodetectors based on p-GaN thin film/n-ZnO based nanowire arrays exhibited a rectification characteristic in darkness and under UV illumination. Under UV illumination, the GIZO device had the best photosensing characteristics of all the devices under 5 V bias. The light-to-dark current ratio was close to 6.0 at 5 V bias and the turn-on voltage was lower than 1.8 V. The presented p-GaN/n-GIZO heterojunction UV photodetector realized superior photoresponse performance at zero-bias voltage as compared to single-doped and un-doped ZnO devices.

Silver nanoprisms/graphene oxide/silicon nanowires composites for R6G surface-enhanced Raman spectroscopy sensor

In this study, Silver nanoprisms/Graphene Oxide/Silicon nanowires (AgNPr/GO/SiNWs) nanocomposites have been fabricated for Surface-Enhanced Raman Spectroscopy (SERS) of Rhodamine 6G (R6G). The SiNWs have been synthesized using the metal-assisted chemical etching method. The surface morphologies of the SiNWs samples have been investigated using scanning electron microscopy. By varying the etching time from 5 to 30 min, the nanowire lengths have been tuned from 2 to 10 µm. While the average nanowire diameter remained unaffected (30-60 nm) with the increase in etching time, increments of nanowires length were found to alter the bundle morphology. The final SERS structure is obtained by depositing the GO layer followed by AgNPr. The obtained SERS sensor exhibited an enhanced efficiency as compared to AgNPr/SiNW matrix. The results demonstrate that a maximum efficiency factor of 6.1×1010 could be achieved with sensor fabricated with 30 min etched SiNWs.

Finite-difference time-domain analysis of the tunability of Anderson localization of light in self-organized GaN nanowire arrays

The possibility of tuning the resonance frequency and photon lifetime corresponding to Anderson localized resonant modes is investigated using the finite-difference time-domain technique. Experimentally obtained dimensions of molecular beam epitaxy grown self-organized nanowires on silicon have been employed to systematically generate disordered patterns, where multiple-scattering mediated light trapping has been analyzed. The results of our analysis indicate that in spite of the inherent randomness of the scattering medium, it is possible to control the wavelength and strength of the localized modes by varying dimensional features of the nanowires. The localization wavelength in the medium can be tuned toward a higher wavelength by increasing the average diameter of nanowires, whereas cavity quality factors in the order of 105 can be attained by increasing the fill factor of the array. The observed behavior is explained and empirically modeled, and the relation is found to be in good agreement with the predicted localization characteristics for experimentally grown self-assembled nanowires. The results of the analysis indicate that in spite of the absence of periodicity, localization in this medium is related to interference effects resulting from Bragg-like diffractions, which in effect results in the observed systematic variation of localization characteristics as nanowire dimensions are varied.

Tuning of transport properties of the double-step chemical bath deposition grown zinc oxide (ZnO) nanowires by controlled annealing: An approach to generate p-type ZnO nanowires

ZnO nanowires/p-Si heterojunction diodes are fabricated by employing low temperature double-step chemical bath deposition technique. The grown samples are initially annealed at different temperatures in the range of 300 °C to 600 °C at 10 psi argon atmosphere for 30 min. Field emission scanning electron microscope images confirmed the growth of vertically oriented ZnO nanowires with average nanowire diameter and height of 183–190 nm and ~1.4 μm, respectively. The x-ray diffraction study shows that the samples are poly-crystalline with hexagonal wurtzite structure and ZnO nanowires are vertically c-axis oriented. The photoluminescence study indicates the presence of oxygen vacancy in as-grown and 300 °C annealed sample, whereas, the 500 °C annealed ZnO nanowires show the existence of oxygen interstitials. Heterojunction diodes are fabricated on the as-grown, 300 °C, 400 °C, 450 °C, 460 °C, 475 °C, 490 °C, 500 °C, 550 °C and 600 °C annealed nanowires for the measurements of current-voltage and capacitance-voltage characteristics. Both the results indicate an electron dominated transport for the as-grown to 490 °C samples and hole transport for ≥500 °C annealed sample. The acceptor or p-type dopant formation temperature is observed to be 500 °C, which shows an effective acceptor concentration of 1.15 × 1015 cm−3 (at 10 kHz) and 1.74 × 1015 cm−3 (at 1 MHz). Thus the work indicates a possible route for converting the n-type ZnO nanowires to p-type of nature.

Glucose-directed synthesis of Pt-Cu alloy nanowires networks and their electro-catalytic performance for ethylene glycol oxidation

Three-dimensional (3D) network structure nanomaterials (NMs) show excellent catalytic performance due to the larger active surface area. A glucose-directed, surfactant-free and one-step direct chemical co-reduction method for synthesis of Pt-Cu alloy nanowires (NWs) under room temperature was demonstrated in present paper. The Pt-Cu NWs were obtained through the co-reduced of CuCl2 and H2PtCl6 by sodium borohydride in the presence of glucose, the glucose in which not only acted as one-dimensional (1D) growth-directing agent, also as the stabilizing agent. The average diameter of NWs was about 3.1 nm and NWs showed typical face-centered-cubic (fcc) alloy crystal structure. The influence of Pt/Cu ions ratios in precursor solution on the bimetallic composition of NWs had been studied, and NWs displayed the feature of composition-tuning. The electro-catalytic activity of Pt-Cu alloy NWs for ethylene glycol oxidation reaction (EGOR) in alkaline medium was strongly related on their compositions. The Pt31Cu69 NWs exhibited about 1.8 times higher than that of commercial Pt/C and higher durability. The enhanced catalytic performance of Pt-Cu alloy NWs was mainly attributed to their unique 3D network structure and the synergetic effects between Pt and Cu.

Template-Free Growth of Well-Ordered Silver Nano Forest/Ceramic Metamaterial Films with Tunable Optical Responses.

Currently, the limitations of conventional methods for fabricating metamaterials composed of well-aligned nanoscale inclusions either lack the necessary freedom to tune the structural geometry or are difficult for large-area synthesis. In this Communication, the authors propose a fabrication route to create well-ordered silver nano forest/ceramic composite single-layer or multi-layer vertically stacked structures, as a distinctive approach to make large-area nanoscale metamaterials. To take advantage of direct growth, the authors fabricate single-layer nanocomposite films with a well-defined sub-5 nm interwire gap and an average nanowire diameter of ≈3 nm. Further, artificially constructed multilayer metamaterial films are easily fabricated by vertical integration of different single-layer metamaterial films. Based upon the thermodynamics as well as thin film growth dynamics theory, the growth mechanism is presented to elucidate the formation of such structure. Intriguing steady and transient optical properties in these assemblies are demonstrated, owing to their nanoscale structural anisotropy. The studies suggest that the self-organized nanocomposites provide an extensible material platform to manipulate optical response in the region of sub-5 nm scale.

Effect of Synthesis Temperature, UV-Ozone Treatment, and Nanowire Diameter on the Failure of Silver Nanowire Electrodes

Silver nanowires (SNWs) have shown much promise as a lower cost flexible transparent electrode alternative to indium tin oxide. However, the stability of SNW electrodes has been brought into question. In this work, we studied the failure of SNW electrodes for different synthesis conditions and nanowire diameters with and without ultraviolet (UV)-ozone treatment. Transparent electrodes fabricated from nanowires synthesized at lower temperatures were found to have a lifetime of 53 days: the longest reported lifetime to the best of our knowledge for electrodes fabricated with nanowires less than 100 nm in diameter. In trials for transparent electrodes fabricated with SNW with average diameters of 80 nm, UV-ozone-treated films reached ultimate failure two days later than nontreated electrodes. This was attributed to the formation of silver oxide on the nanowires, which served as a protective layer and slowed the degradation process. Scanning electron microscope (SEM) images showed SNW electrodes made with an average nanowire diameter of 80 nm failed due to broken connections at the nanowire junctions. On the other hand, SNW electrodes made with an average diameter of 233 nm failed along the nanowires themselves, which suggests a different failure mechanism. The UV-ozone-treated larger diameter nanowire electrodes failed after 127 days, and the failure date of the nontreated SNW electrode remained undetermined after 153 days of continuous operation.

Synthesis, phase composition, and magnetic properties of iron nanowires prepared in the pores of polymer track-etched membranes

Arrays of iron nanowires prepared by the method of galvanic filling of polymer track-etched membrane pores (matrix synthesis) under different electrolysis modes and electrolyte temperatures have been studied. The conditions of the synthesis have been analyzed. The optimal composition and electrolyte temperature have been found. The phase composition and magnetic properties of nanowires have been studied using the methods of electron microscopy, X-ray diffraction, elemental energy-dispersive microanalysis, and Mossbauer spectroscopy. The average nanowire diameter is 100–200 nm. The length varies from 6 to 10 μm. The surface density is ∼108 cm−2 at the average distance to each other of about 1 μm. It has been established that the basis of nanowires is formed by the metal iron nanocomposite that manifests the magnetic properties of bulk α-Fe. It has been found that the preferred orientation of the magnetization inside the iron nanowires arises for an array prepared at a potential of −750 mV.

Fabrication of palladium nanowires using biomolecules as templates

Great attention has been paid to the palladium metal nanowires due to their wide potential application, in particular, as gas sensors and chemical reaction catalyst. In this work, the insulin fibrils were initially obtained by incubating the insulin peptides at 70℃ for 25 h. Then, the palladium oxide nanowires were synthesized by co-incubating the three-day-aged palladium chloride solution with pre-formed insulin fibrils for half an hour. Simply by adjusting the aging temperature of palladium chloride solution, the size of palladium oxide nanowires could be well controlled. The average diameter of nanowires varied from 7.5 to 20.1 nm as evaluated by atomic force microscopy. Finally, the palladium metal nanowires were successfully achieved by heating the sample up to 600℃ under the hydrogen atmosphere and keeping for 2 h before cooling down to room temperature. In addition, the X-ray photoelectron spectroscopy was also used to characterize the chemical composition of the fabricated palladium metal nanowires.

Crystallinity and morphological evolution of hydrothermally synthesized potassium manganese oxide nanowires

Potassium manganese oxide (KMn8O16) nanowires were synthesized using a customized hydrothermal method and characterized using scanning-electron microscopy, X-ray diffractometry and thermogravimetric analysis to determine the effects of reaction temperatures and molar ratio of reactants on the crystallinity and morphology of the synthesized nanowires. It was established that increasing the stoichiometric portion of potassium precursors increased the average nanowire diameter though such effect was comparatively less prominent in terms of reaction temperature. Deficient supply of potassium inhibited nanowires growth in which only KMn8O16 (cryptomelane) growth orientations of (211), (301) and (600) were observed along with traces of MnO2, resulting in a wool-like nanowires suspension.

Shape-Controlled Vapor-Transport Growth of Tellurium Nanowires

A vapor transport method is employed to synthesize single crystalline tellurium nanowires with tailorable size using tellurium powder in an inert atmosphere. The average nanowire diameter is tunable between 50 and 3000 nm with an associated length of 1 to 22 μm. Growth temperature and time are used to specifically control the behavior of supersaturation, leading to nucleation and morphological control in this vapor–solid growth regime. Analysis of the resulting nanowire product provides insight into the dominant reaction kinetics involved in these growths and suggests routes by which to control growth product. This methodology provides a practical approach to synthesizing high-quality tellurium nanowires of various sizes and their incorporation into two-dimensional mesh-like structures through controlled nucleation and growth dynamics.

Controlled Lateral Growth of Silica Nanowires and Coaxial Nanowire Heterostructures

Silica nanowires, grown on gold-coated silicon substrates by the active oxidation of silicon, are shown to undergo an initial stage of rapid longitudinal growth, followed by a stage of sustained lateral growth. During lateral growth, the average nanowire diameter increases linearly with annealing time and proceeds uniformly along the nanowire length at a rate of order 2 nm/min, thereby providing a simple and effective means of control. These observations are discussed with regard to predictions of a simple growth model based on the kinetic theory of ideal gases and are shown to provide a useful process for fabricating more complex silica-based coaxial core–shell heterostructures.

Magnetic characterization of nickel-rich NiFe nanowires grown by pulsed electrodeposition

Nickel-rich NiFe nanowires with well-controlled diameters and compositions are fabricated in various porous alumina templates by using a pulsed electrochemical deposition technique. The average pore diameter of the templates is tuned either by coating the pore walls with thin silica layers using an atomic layer deposition (ALD) technique or by applying a chemical pore widening process. The composition of the alloy is controlled by varying the frequency of the deposition pulse. The coercivity of the nanowire array is influenced by its texture and the amount of iron content in the alloy. The effective field and the saturation magnetization are found to be reinforced with the decrease in Ni content. A distinct enhancement of the axial coercivity and squareness of permalloy, Ni80Fe20, nanowire array are obtained by decreasing the average nanowire diameter. The processes of magnetization reversal in Ni80Fe20 nanowire array are investigated. The temperature dependence of Ni80Fe20 nanowires coercivity is interpreted in accordance with magnetization fluctuation over a single energy barrier.

High-Performance Transparent Conductors from Networks of Gold Nanowires

We report the deposition and characterization of thin networks of gold nanowires on plastic substrates. The average nanowire diameter was 47 nm, while the networks had mean thicknesses in the range of 35–750 nm. The conductivity of networks with mean thicknesses below 100 nm was controlled by percolation, as characterized by the percolation exponent, n = 0.8, and the percolative figure of merit, Π = 28. However, networks with thicknesses above 100 nm had thickness-independent direct current conductivity of σDC,B = 5.4 × 105 S/m. The conductivity was limited by junction resistances, which we estimate at ∼3 kΩ. Networks of all thicknesses were described by an optical conductivity of σOp = 1.0 × 104 S/m. These electrical and optical properties result in networks with sheet resistance and transmittance very close to industry requirements, that is, 49 Ω/□ @ 83%. These values are superior to almost all reported carbon nanotube networks and are competitive with silver nanowire networks. We measured the work func...

Fabrication of diameter-modulated and ultrathin porous nanowires in anodic aluminum oxide templates

Anodic aluminum oxide (AAO) membranes with modulated pore diameter were synthesized by pulse anodization in 0.3M sulfuric acid at 1°C. For AAO growth, a typical combination of alternating mild anodizing (MA) and hard anodizing (HA) pulses with applied potential pulses of 25V and 35V was applied. The control of the duration of HA pulses will provide an interesting way to tune the shape of pores and the structure of AAO channels. It was found that a non-uniform length of HA segments in cross section of AAO is usually observed when the HA pulse duration is shorter than 1.2s. The pulse anodization performed with longer HA pulses leads to the formation of AAO templates with periodically modulated pore diameter and nearly uniform length of segments. Various diameter-modulated metallic nanowires (Au, Ag, Ni and Ag–Au) were fabricated by electrodeposition in the pores of anodic alumina membranes. A typical average nanowire diameter was about 30nm and 48nm for MA and HA nanowire segments, respectively. After a successful dealloying silver from Ag–Au nanowires, porous ultrathin Au nanowires were obtained.

Influence of Growth Parameters on the Morphology and Magnetic Property of SnO2 Nanostructures

In this paper, we report the room-temperature ferromagnetism (FM) of a pure nanostructure with various morphologies synthesized by a chemical vapor deposition (CVD) method and study the growth condition dependences of morphology and magnetic property. As the growth temperature is increased from 700 to , the average diameter of nanowires (NW) increases from 20 to 60 nm, while magnetization decreases from 0.223 to 0.081 emu/g. However, morphology and FM are not sensitive to the argon flow rate during the CVD synthesis. Selected area electron diffraction, X-ray diffraction, and X-ray photoelectron spectroscopy measurements show that all the samples possess a typical rutile structure, and no other impurity phases are observed. The results demonstrate that the ferromagnetic properties of the samples are related to the morphology and exhibit an increment trend with the increasing surface-to-volume ratio. With a combined study of photoluminescence, our results reveal that the oxygen vacancies mainly at the surface of NW contribute to the FM of nanostructures.

Effect of seed layer on the growth of well-aligned ZnO nanowires

We demonstrate that vertical well-aligned crystalline ZnO nanowire arrays were grown on ZnO/glass substrates by a low-temperature solution method. Different thicknesses of ZnO seed layers on glass substrates were prepared by radio-frequency sputtering. In this work it was found that the morphology of ZnO nanowires strongly depends on the thickness of ZnO seed layers. The average diameter of nanowires is increased from 50 to 130 nm and the nanowire density is decreased from 110 to 60 μm −2 while the seed layer thickness is varied from 20 to 1000 nm. The improved control of the morphology of ZnO nanowire arrays may lead to an enhanced carrier collection of hybrid polymer photovoltaic devices based on ZnO.

Cascade processes in inelastic light scattering in ZnSe nanowire structures

The resonance Raman scattering of light in MBE-grown structures with ZnSe nanowires (10–20 nm in diameter) with an Au film deposited on the substrate used as a catalyst was investigated. The thicknesses of the Au layers were 2, 10, and 100 A. The photon energy of the He-Cd pump laser (λ = 441.6 nm) was in excess of the band gap of bulk ZnSe, and the measurements were conducted at room temperature. Under these conditions, the Raman spectra are defined by a cascade process in which the electron interacting with a longitudinal optical phonon transfers between real band states with a certain probability of radiative recombination at each step. The blue shift of the luminescence maximum associated with the quantum confinement of carriers in the nanowire has been observed. The average nanowire diameter derived from the magnitude of this shift agrees well with electron microscopy measurements.

Growth of Ga2O3 and GaP nanowires synthesized from mixed Ga/GaP powder as a precursor

High-purity gallium oxide (β-Ga2O3) and/or gallium phosphide (GaP) nanowires were synthesized on the nickel or the cobalt oxide catalyzed alumina substrate by a simple chemical vapor deposition method from a mixture of gallium (Ga) and gallium phosphide powder as a source materials. The source materials were directly vaporized in the range of 750–1000°C for 60min under argon ambient. The average diameter of nanowires in the optimum synthesis temperature was around 70nm and the length was up to several hundreds of micrometer. We confirmed that β-Ga2O3 nanowires were observed in all samples, while the GaP nanowires with β-Ga2O3 nanowires were only obtained in the sample synthesized on the nickel oxide catalyst at 950°C. The β-Ga2O3 and GaP nanowires have a single-crystalline monoclinic and zinc blend structure, respectively. And the both nanowires reveal the core–shell structure, which consists of the β-Ga2O3 or GaP core and the amorphous gallium oxide outer layer.