Pure Nanowires Research Articles

Multiferroic properties of Tb-doped BiFeO3 nanowires

Nanoscale, multifunctional, multiferroic materials possess strong magnetoelectric coupling (ME), open exciting multitudinous ways for designing future nanoelectronic and spintronic device applications. Bulk nanowires (100 nm), pure, and Tb-doped BiFeO3 multiferroic nanowires (20 nm) have been synthesized by colloidal dispersion template-assisted technique. The effects of Tb-doping and size of synthesized nanowires on structural, electrical, magnetic, dielectric, and magnetodielectric properties have been investigated. X-ray diffraction study reveals that doping of Tb in BiFeO3 nanowires leads to structural transformation from rhombohedral to orthorhombic. X-ray photoemission analysis confirms the +3 oxidation state of Fe and high purity of samples. Bulk nanowires exhibit antiferromagnetic characteristics, whereas the Tb-doped BiFeO3 nanowires show ferromagnetic character. Moreover, with increase in Tb concentration, the saturation magnetization increases. Temperature-dependent magnetization study suggests their size-dependent ferro and ferri-magnetic behavior. Polarization versus electric field (P–E) study reveals that pure BiFeO3 nanowires possess elliptical loop; however, doping of Tb results in rectangular loop— portentous good ferroelectric properties. All synthesized samples exhibit frequency-dependent dielectric constant which decreases with increase in frequency and remains fairly constant at higher frequencies. Leakage current density decreases with increase in Tb concentration, and has been found to be three orders of magnitude less than those of bulk BiFeO3 nanowires. The ME coupling in synthesized nanowires was estimated by measuring magnetodielectric. A very high value of ME, 7.2 %, has been found for 15 % Tb-doped BiFeO3 nanowires. In this communication, we, for the first time, report new cue on size-dependent Tb-doped BiFeO3 nanowires, which may be further used to explore its technological device applications.

Enhanced ethanol sensing properties of multiple networked Au-doped In2O3 nanotube sensors

In2O3 nanotubes were synthesized as gas sensors using TeO2 nanowires as a template. Scanning and transmission electron microscopy revealed the tubes to have diameters of a few hundred nanometers, wall thickness of ∼25nm and lengths up to a few millimeters. Multiple networked Au-doped In2O3 nanotube sensors showed responses of 187–1219% to 50–250ppm C2H5OH at 300°C. These responses are far superior to those obtained by undoped In2O3 nanotubes and stronger than those obtained by pure In2O3 nanowires at 370°C. In addition, the ethanol sensing mechanism of the Au-doped In2O3 nanotube sensors is discussed.

Numerical modeling of a CNT–Cu coaxial nanowire in a vacuum to determine the thermal conductivity

A molecular dynamics simulation is created to predict the thermal conductivity of a (7,7) single wall carbon nanotube filled with a copper nanowire for lengths ranging from 9.957nm to 63.091nm. In the simulations, a temperature difference is created using Nose–Hoover thermostats at the two ends with 320K and 280K. The thermal conductivity of the carbon nanotube–copper nanowire nanostructure is calculated to be 24% higher than that of a corresponding pure single wall carbon nanotube and estimated to be 40% lower than that of a pure copper nanowire.

Template-Free Fabrication and Thermoelectric Properties of PbSe Modified Poly(<I>p</I>-phenylenediamine) Nanowires

In this paper, we presented a template-free method to prepare poly(p-phenylenediamine) (PpPD) nanowires. PpPD nanowires were synthesized by chemical oxidative polymerization in aqueous solution, using ammonium persulfate as initiator and beta-naphthalenesulfonic acid as soft template. The obtained polymer powder was treated with Pb(NO3)2 and Na2SeSO3 solutions in sequence to form PbSe nanoparticle modified PpPD. The products were characterized by X-ray powder diffraction, infrared spectroscopy, and transmission electron microscopy, respectively. The thermoelectric properties of the powders after cold pressing were measured at room temperature. The pure dedoped PpPD nanowires exhibited very large Seebeck coefficient (2692 microV K(-1)) but very low electrical conductivity. As the PbSe content increased, the electrical conductivity of the PbSe/PpPD composite increased, whereas the Seebeck coefficient decreased, and the power factor monotonically increased. The sample with 41.5 wt% PbSe had a highest power factor, 0.189 microW m(-1) K(-2) which is -270 times as large as that of the pure PpPD nanowires (8.7 x 10(-4) microW min(-1) K(-2)).

Synthesis and Electrochemical Properties of Sb<SUB>2</SUB>Se<SUB>3</SUB> Nanowires Prepared by a Gas Induced Reduction Method

Sb2Se3 nanowires have been prepared by a novel gas induced reduction (GIR) method. The precursor solution prepared by dissolving Sb2(OCH2CH2O)3 and SeO2 in a certain solvent was initially separated from the reductant, hydrazine hydrate. The reductant evaporated during the heating process, dissolved into the precursor solution and reacted with Sb3+ and SeO2 and finally Sb2Se3 nanostructures formed. Different solvents including diethanolamine, glycerol, ethylene glycol, deionized water, absolute ethanol and isopropyl alcohol were respectively used for comparison. It was found that when ethylene glycol was used as a solvent, pure, relatively homogeneous, and high aspect-ratio Sb2Se3 nanowires (40-120 nm in diameter and -100 microm in length) were prepared. Growth mechanism of the Sb2Se3 nanowires was proposed. The electrochemistry character of the nanowires was investigated via assembling into lithium ion batteries. The discharge capacity of Sb2Se3/Li cell cycled between 0.3 and 2.5 V was performed in the range of 142-1036 mA x h x g(-1) during the first 30 cycles, with the charge/discharge efficiency increasing from 89.4% to 97.5%.

Structural, dielectric and magnetic characterization of large scale template synthesized Gd doped BiFeO3 nanowires

Pure and 10 % Gd doped BiFeO3 nanowires of 100-nm diameter have been synthesized by sol–gel template-assisted technique. Phase-dependent structural, dielectric and magnetic properties of pure and Gd doped BiFeO3 nanowires have been investigated. X-ray diffraction study reveals that pure BiFeO3 nanowires possess rhombohedral structure while 10 % Gd doped BiFeO3 nanowires are orthorhombic in nature. Magnetic study confirms that the value of saturation magnetization, increased with structural change via doping of Gd in host BiFeO3.

A Preliminary Study on the Synthesis and Characterization of Multilayered Ag/Co Magnetic Nanowires Fabricated via the Electrodeposition Method

A single-bath electrodeposition method was developed to integrate multilayer Ag/Co nanowires with a commercial anodic alumina oxide (AAO) template with a pore diameter of 100–200 nm. An electrolyte system containing silver nitride and cobalt sulfide was studied using cyclic voltammetry, and the electrodeposition rate was varied to optimize the electrodeposition conditions. A constant stepwise potential and a variable cation ratio of [Co2+]/[Ag+] were used during electrodeposition. After the dissolution of the template in aqueous NaOH solution, multilayered Ag/Co nanowires were obtained with a composition of [Co]/[Ag80Co20], as identified by XRD and TEM, when [Co2+]/[Ag+] = 150. By annealing at 200°C for 1 h, uniformly structured (Co99.57/Ag100) nanowires were obtained. Compared with pure Co nanowires, the magnetic hysteresis loops showed a greater magnetic anisotropy for (Co99.57/Ag100) nanowires than for pure Co nanowires, corresponding to a change in the easy axis upon magnetization.

Selective growth of pure magnetite thin films and/or nanowires grown in situ at a low temperature by pulsed laser deposition

Pure Fe3O4 thin films and/or nanowires were selectively grown onto c-Al2O3 (0001) substrates in situ at different substrate temperatures using pulsed laser deposition (PLD). The epitaxial Fe3O4 thin films were grown at deposition temperatures that ranged from 300 to 600 °C, while nanowires with a single-crystalline nature were grown at temperatures of more than 600 °C without catalysts. The in-plane compressive stress of the films increased as deposition temperature increased. Protrusions to relieve the compressive stress typically formed at the low-angle grain boundaries and were then developed to make nanowires. Both the films and the nanowires showed a ferromagnetic nature and a magnetic anisotropy at room temperature.

Study on Charge Carriers Behavior at CdS/TiO2Interface of One Dimensional TiO2@CdS Core-shell Structure by Raman Scattering and Surface Photovoltage Spectroscopy

TiO 2 nanowires with the diameter of about 90 nm and length of dozens of micron meter were synthesized by thermal annealing of Ti foil under the catalysis of Pd nanoparticles which were deposited on Ti foil with the ultraviolet light photoreduction. CdS shell grew on the surface of TiO2 nanowires by chemical bath deposition (CBD) to form the 1D TiO2@CdS core/shell nanostructures. The thickness of CdS shell was controlled by varying the concentration of the citric acid. The scanning electron microscope (SEM) and transmission electron microscope (TEM) characterization implied that CdS shell thickness on TiO2 nanowire were about 20, 30 and 60 nm, synthesized in the solutions with citric acid concentra- tion of 0.095, 0.19 and 0.38 mmol/L, respectively. The Raman scattering of pure TiO2 nanowire and TiO2@CdS core/shell structures excited by 488 nm Argon ion laser indicates that the modification of CdS on TiO2 nanowire with proper thickness (20 to 30 nm) can increase both the Raman scattering resulted from CdS and TiO2. It is attributed to the photo-induced elec- tron transfering from CdS shell and TiO2 core, which results in the quenching of fluorescence of CdS, and the increase of electron distribution density for TiO2 excited state. The surface photovoltage (SPV) spectrum characterization, based on the separation of photo-generated electron-hole in space, agrees well with the Raman scattering results. That is, TiO2@CdS core/shell structures with 30 nm CdS have highest SPV response intensity and broadest spectrum range, due to the effective charge transfer between CdS and TiO2. The systematic study about the dependence of the Raman scattering and SPV on the CdS shell thickness demonstrated that the diffusion length of electron in CdS shell is between 30 and 60 nm, and it is optimal for one-dimension TiO2@CdS nanostructures in optoelectric devices application with the CdS shell thickness thinner than light penetration depth and electron diffusion length in CdS. Keywords TiO 2 nanowire; TiO2@CdS; Raman scattering; surface photovoltage spectroscopy (SPS)

Surface plasmon resonance enhanced band-edge emission of CdS–SiO2core–shell nanowires with gold nanoparticles attached

Inspired by the good match between the surface-plasmon energy of Au nanoparticles and the emitted photon energy of CdS nanowires, CdS–SiO2 core–shell nanowires with Au nanoparticles attached (CdS–SiO2–Au) were prepared to investigate the interaction between the semiconductor and the metal. Photoluminescent and lifetime measurement reveal that the band-edge emission of CdS nanowires in this hybrid structure has a fivefold enhancement compared with pure CdS nanowires due to the surface plasmon resonance. In addition, the existence of an optimized thickness of the SiO2 layer for the emission enhancement indicates that the interactions between the metal and the semiconductor occur constructively only at appropriate distances. These CdS–SiO2–Au nanowires with tailored morphologies and enhanced band-edge emission have potential applications in solar cells, photodetectors and bio-nanotechnology.

Low temperature growth of SnO2 nanowires by electron beam evaporation and their application in UV light detection

For the first time, high quality tin oxide (SnO2) nanowires have been synthesized at a low substrate temperature of 450°C via vapor–liquid–solid mechanism using an electron beam evaporation technique. The grown nanowires have shown length of 2–4μm and diameter of 20–60nm. High resolution transmission electron microscope studies on the grown nanowires have shown the single crystalline nature of the SnO2 nanowires. We investigated the effect of growth temperature and oxygen partial pressure on SnO2 nanowires growth. Variation of substrate temperature at a constant oxygen partial pressure of 4×10−4mbar suggested that a temperature equal to or greater than 450°C was the best condition for phase pure SnO2 nanowires growth. The SnO2 nanowires grown on a SiO2 substrate were subjected to UV photo detection. The responsivity and quantum efficiency of SnO2 NWs photo detector (at 10V applied bias) was 12A/W and 45, respectively, for 12μW/cm2 UV lamp (330nm) intensity on the photo detector..

Synthesis and photoluminescence of pure and Mn doped CdS nanowires

Pure and Mn doped CdS nanowires were synthesized by a convenient thermal evaporation method. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) were used to examine the morphology, phase structure, crystallinity and composition. PL spectra were used to investigate emission properties of the as-prepared samples. Only near band gap emission is observed in pure CdS nanowire. There are near band gap emissions and T14→A16 transition emissions of Mn2+ in doped CdS nanowire with low dopant concentration, although near band gap emission is dominant. However, near band gap emission is too weak to be detected and only Mn2+ related emissions are observed when dopant concentration reaches 0.83%. The corresponding emission color changes from green to orange.

Phase-dependent multiferroism in Dy-doped BiFeO3 nanowires

Nanostructured multiferroics, multifunctional materials owning to their smaller size and the strong magnetoelectric coupling, open exciting innumerable ways for designing future nanoelectronic and spintronic device applications. Pure and 15% Dy-doped BiFeO3 nanowires of 20-nm size have been synthesized by colloidal dispersion template-assisted technique. Phase-dependent magnetic, electric and multiferroics properties of pure and Dy-doped BiFeO3 nanowires have been investigated. X-ray diffraction study reveals that pure BiFeO3 nanowires possess rhombohedral structure; however, 15% Dy-doped BiFeO3 nanowires are orthorhombic. X-ray photoemission analysis confirms the +3 oxidation state of Fe (Fe3+) and high purity of samples. Magnetic study confirms that the synthesized nanowires exhibit ferromagnetic behaviour, and, that the value of saturation magnetization, increased with structural change and doping of Dy in host BiFeO3. Polarization versus electric field study clearly reveals that the pure BiFeO3 nanowires possess elliptical loop due to leaky behaviour but 15% Dy-doping results in well saturated rectangular loop. Leakage current density decreases with increase in Dy doping. The magnetoelectric coupling in the synthesized nanowires has been estimated by magnetodielectric measurement. High value of magnetodielectric coefficient, 4.85%, has been observed for 15% Dy-doped BiFeO3 nanowires. In this communiqué, we are for the first time reporting a new cue on phase-dependent multiferroic properties of Dy-doped BiFeO3 nanowires, which may prove to be a potential candidate for future technological device applications.

Ag/TiO2 core–shell nanocables prepared with a one-step polyol process

One-dimensional (1D) Ag/TiO2 core–shell nanocables have been synthesized with a facile polyol process by reducing AgNO3 and hydrolysis of titanium tetraisopropoxide without the need for any templates and capping agents under atmospheric conditions. The morphology of the Ag/TiO2 core–shell nanocables produced in this way is as either linear or spiral particles. The former are composed of an Ag rod core, and the later are aggregates of Ag nanoparticles which are aligned into an ID structure. The nanocables are about 50 and 150 nm in diameter for the linear and spiral particles, respectively, and over 30 μm in length. The absorption peaks of these Ag/TiO2 core–shell nanocables are significantly red-shifted comparing with those of uncoated pure silver nanowires. On the basis of the experimental results, a micro-reactor oxide template mechanism has been proposed to explain the growth of Ag/TiO2 core–shell nanocables.

Dual-Band Noise Suppressors Based on Co/Au Multilayered Magnetic Nanowires

Co/Au multilayered magnetic nanowires with a diameter of 200 nm were electrodeposited into nanoporous anodic aluminum oxide (AAO) templates. Coplanar waveguide transmission lines were patterned on the AAO templates that were filled with the Co/Au nanowires. Noise suppressors based on pure Co and Au nanowires were also fabricated as references. The transmission coefficient S21 of the device based on Co nanowires showed an absorption peak due to the loss of ferromagnetic resonance; S21 of the device based on Au nanowires decreased linearly with increasing frequency due to the loss of eddy current. S21 of the noise suppressors based on Co/Au multilayered nanowires showed a dual-band absorption phenomenon, because of the ferromagnetic resonance of the nanowires and the periodicity of the magnetic/nonmagnetic nanostructure. The frequencies of the two absorption peaks were 24-25 GHz and 36-38 GHz, which indicated that the working frequency of the microwave devices could be beyond 20 GHz.

Ultraclean Emission from InAsP Quantum Dots in Defect-Free Wurtzite InP Nanowires

We report on the ultraclean emission from single quantum dots embedded in pure wurtzite nanowires. Using a two-step growth process combining selective-area and vapor-liquid-solid epitaxy, we grow defect-free wurtzite InP nanowires with embedded InAsP quantum dots, which are clad to diameters sufficient for waveguiding at λ ~ 950 nm. The absence of nearby traps, at both the nanowire surface and along its length in the vicinity of the quantum dot, manifests in excitonic transitions of high spectral purity. Narrow emission line widths (30 μeV) and very-pure single photon emission with a probability of multiphoton emission below 1% are achieved, both of which were not possible in previous work where stacking fault densities were significantly higher.

A novel facile synthesis and characterization of molybdenum nanowires

We describe a straightforward technique to synthesize pure Mo nanowires (NWs) from Mo6SyIz (8,2 <y + z ≤ 10) NWs as precursor templates. The structural transformations occur when Mo6SyIz NWs are annealed in Ar/H2 mixture leading to the formation of pure Mo NWs with similar structures as initial morphologies. Detailed microscopic characterizations show that large diameters (>15 nm) Mo NWs are highly porous, while small diameters (<7 nm) are made of solid nanocrystalline grains. We find NW of diameter 4 nm can carry up to 30 μA current without suffering structural degradation. Moreover, NWs can be elastically deformed over several cycles without signs of plastic deformation.

Tuning emission property of CdS nanowires via indium doping

Pure and doped CdS nanowires were synthesized by a convenient thermal evaporation method. SEM, XRD, TEM and EDS were used to examine the morphology, phase structure, crystallinity and composition. PL spectra were used to investigate emission properties of the as-prepared samples. We observe near band gap and trapped state emission in doped CdS nanowires while only near band gap emission in pure CdS nanowires. Moreover, the trapped state emission intensity increase with In dopant concentration and the emission color change from green to orange. The intensity of near band gap emission was too weak to be observed and only trapped state emission was detected when In concentration reach to 0.89%.

Growth of germanium nanowires from bis(acetylacetonato) dichloro germanium

Germanium nanowires were grown by chemical vapor deposition from a bis(acetylacetonato) dichloro germanium precursor. The advantages of this precursor are that it is a solid and sublimes at a relatively low temperature to produce pure germanium nanowires. The nanowires were grown on different substrates such as silicon and quartz and their diameters vary from 20 to 200nm. X-ray diffraction, Raman and transmission electron microscopy analyses show that the nanowires are crystalline and exhibit germanium crystal structure.

Room temperature synthesis and photocatalytic property of AgO/Ag2Mo2O7 heterojunction nanowires

AgO/Ag2Mo2O7 heterojunction nanowires were synthesized at temperatures of 25°C, 50°C, 80°C, and 110°C, under magnetic stirring in solution reaction. The catalytic activity of AgO/Ag2Mo2O7 nanowires was evaluated by the degradation of Rhodmine B dye under the irradiation of the simulated sunlight. The synthesized samples were characterized by X-ray diffractometer, energy dispersive spectrometry, X-ray photoelectron spectrometer, scanning electron microscopy, and transmission electron microscopy. The results show that the AgO nanoparticles are attached on the surface of the Ag2Mo2O7 nanowires to form a heterojunction structure. The length of the nanowires is up to 10μm and the size of the AgO nanoparticles is 10–20nm. The length of nanowires increases with increasing reaction time and temperature while the AgO particles are gradually embedded into the nanowires. The photocatalytic activity is greatly improved for the AgO/Ag2Mo2O7 heterojunction nanowires compared with that of the pure Ag2Mo2O7 nanowires, indicating a remarkable role of AgO particles on the Ag2Mo2O7 nanowires in the photodegradation.