Ni-Pt multilayered nanowire arrays with enhanced coercivity and high remanence ratio

Highly ordered Ni-Pt multilayered nanowire arrays have been fabricated using a porous anodic aluminum oxide (AAO) template by pulse electrodeposition. The cylindrical Ni nanoparticles with different lengths and diameters in these arrays were characterized by transmission electron microscope (TEM) and alternating-gradient magnetometer (AGM) measurements. Magnetization measurements revealed that an array of such nanowires with 20-nm diameters has an enhanced coercivity (ca. 1169 Oe) and a high remanence ratio (ca. 0.96).     

Co、Ni及其合金纳米线阵列的制备及磁性研究

采用交流电化学沉积法,在多孔阳极氧化铝(AAO）模板孔洞中成功组装了铁磁性金属Co、Ni、CoNi合金纳米线阵列并采用扫描电子显微镜(SEM）、X射线衍射(XRD）等对样品进行表征。结果表明,Co、Ni及CoNi合金阵列体系中纳米线均匀有序,形状各向异性较大(长径比达30以上）,有显著的结晶择优取向。对Co、Ni、CoNi合金纳米线阵列体系进行磁性分析,振动样品磁强计(VSM）测试结果显示,纳米线有明显的磁各向异性,适合用作垂直磁记录介质。纳米线阵列退火后沿纳米线方向矫顽力和矩形比减小,样品的垂直磁各向异     

热处理对[NiFe/Cu/Co/Cu]_n多层纳米线磁性能的影响

采用双槽控电位法在阳极氧化铝(AAO)模板中制备了有序均一的[NiFe/Cu/Co/Cu]n多层纳米线阵列,并在不同温度下进行了热处理.利用X射线衍射(XRD)对热处理前后多层线的晶体结构进行了测试.考察了不同退火温度对多层线矫顽力、剩磁比、巨磁电阻(GMR)效应、磁灵敏度的影响.随热处理温度升高,多层纳米线中磁性微晶晶型取向越来越明显,晶体结构更均匀;多层纳米线的矫顽力和剩磁比先增大后减小.300°C下多层纳米线矫顽力达到最大值,GMR最大值可达59%,对应的磁电阻灵敏度(SV)为0.233%Oe-1.     

One-pot synthesis and magnetic, electrical properties of single-crystalline α-MnS nanobelts

α-MnS single-crystalline nanobelts were synthesized for the first time on a large scale by solvothermal method in monosurfactant dodecylamine system. The investigation of magnetic properties shows antiferromagnetic transition temperature of as-synthesized α-MnS nanobelts is remarkably lower than that of bulk counterparts (152 K) and higher than that of corresponding nanoparticles (18 K). These single-crystalline α-MnS nanobelts exhibit higher coercivity (4013 Oe) than those of reported MnS nanowires (1020 Oe) and nanoparticles (330 Oe). The study on electrical transport shows that the conductivity of individual α-MnS nanobelt is as high as 3.2 × 10⁵ S/m.     

Novel electrodeposition behavior of Ni on porous anodic alumina templates without a conductive interlayer

During template-assisted electrodeposition, single-crystalline metallic nanowires could be obtained only when the overpotential is low. However, an unusual electrodeposition behavior on the PAA/Si substrate without a conductive interlayer between the template and Si is described in the present study. Through the electrical breakdown of the template, Ni nanodots, nanowires and nanotubes could be obtained by only changing the electrodeposition voltage on the same substrate. The mechanisms leading to the formation of various nanostructures are described in detail and compared with those for the conventional template-assisted electrodeposition process. The electrodeposition first occurred on the pore wall instead of from the underlying substrate, leading to the formation of some Ni nanotubes at a more negative voltage. Besides, single-crystalline Ni nanowires could also be formed even when the electrodeposition voltage was as negative as -40 V, indicating that the formation of single-crystalline metallic nanowires under a large overpotential is possible.     

Unconventional zigzag indium phosphide single-crystalline and twinned nanowires

Unconventional zigzag indium phosphide (InP) single-crystalline and twinned nanowires were produced via thermal evaporation of indium phosphide in the presence of zinc selenide. The structure and morphology of the as-synthesized products were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Studies found that two type of nanowires exist in the products, namely, the periodic-rhombus-decorated single-crystalline InP (type I) nanowires and jagged twinned InP (type II) nanowires. Both of them have preferential 111 growth directions. The optical properties were also investigated at room temperature, and they show that the nanowires display a strong emission at approximately 750 nm, which is quite different from that observed in all previous reports related to the InP nanostructures.     

Helical structure of single-crystalline ZnGa2O4 nanowires

Two unique helical zinc gallate (ZnGa2O4) nanostructures were synthesized by thermal evaporation using the zinc selenide (ZnSe) nanowires; helical ZnGa2O4 nanowire rolls either on a straight ZnSe nanowire support or without any support. They all consist of single-crystalline cubic ZnGa2O4 crystals without any dislocation over the entire helical structure and have four equivalent growth directions of 011 with the axial direction of [001]. We suggest that the lattice matching with the ZnSe nanowires would be an important factor in determining the growth direction of the helical ZnGa2O4 nanowires.     

双槽法电沉积Cu/Ni多层纳米线有序阵列

以多孔阳极氧化铝（AAO）为模板，采用双槽法电沉积工艺制得高度有序的Cu/Ni多层纳米线阵列。利用扫描电镜（SEM）和透射电镜（TEM）对Cu/Ni多层纳米线进行了表征，观察到纳米线表面平滑，多层结构清晰，各子层厚度均匀，直径约为 100 nm，与AAO模板孔径基本一致。由选区电子衍射（SAED）照片可知，多层纳米线中Cu层和Ni层均为单晶结构。振动样品磁强计（VSM）测试结果表明，Cu/Ni多层纳米线阵列具有明显的垂直磁各向异性，外加磁场垂直和平行于AAO模板表面时，磁滞回线的矩形比分别为 0.701 和 0.101 ，矫顽力分别为 589 Oe和 202 Oe。通过控制铝阳极氧化工艺及电沉积时间，可获得不同直径、不同子层厚度的Cu/Ni多层纳米线阵列。     

Solvothermal synthesis and characterization of uniform CdS nanowires in high yield

Large-scale CdS nanowires with uniform diameter and high aspect ratios were synthesized using a simple solvothermal route that employed CdCl₂ and S powder as starting materials, ethylenediamine (en) as the solvent. X-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) images show that the products are hexagonal structure CdS nanowires with diameter of 40 nm and length up to 10 μm. Selected area electron diffraction (SAED) and high resolution TEM (HRTEM) studies indicate the single-crystalline nature of CdS nanowires with an oriented growth along the c-axis direction. The optical properties of the products were characterized by optical absorption spectra and photoluminescence spectra. Based on the results of contrastive experiments, it is found that the sulfur source and the solvent play significant roles in the formation of uniform nanowires. A possible formation mechanism of nanowires is discussed.     

气氛对MnCr2O4尖晶石纳米线生长的影响

建立了一种在氮气和氢气的还原性混合气氛和1100 ℃条件下加热商业不锈钢箔(304)制备MnCr2O4尖晶石纳米线的简单方法, 并研究了不同气氛对纳米线生长的影响. 研究发现, 混合气体中氢气含量的变化会影响纳米线的形貌和产率; 而氧化性气氛(如空气)下则得不到纳米线. 在还原性气氛下, Mn和Cr原子可以和反应室内残留的痕量氧反应生成MnCr2O4尖晶石, 而Fe和Ni原子不能被氧化, 但是Fe和Ni可以起到催化纳米线生长的作用, 纳米线的生长机理属于自催化性的气-液-固(VLS)机制.     

Inducing growth of FeNi-Pt match-like magnetic nanoheterostructures on Pt nanotips and dechlorination of hydrochloric ether

Newly designed magnetic FeNi-Pt match-like heterostructured nanorods were synthesized by means of induced growth of FeNi nanorods on Pt nanotips. The proposed synthesis mechanism is corroborated by SEM, TEM, XRD and XPS. The magnetic behavior shows that the magnetic saturation and coercivity are strongly dependent on both the shape and the alloy composition. The saturation magnetizations (Ms) and the coercivity (Hc) of nanorods synthesized are larger than those of nanoparticles because of the relatively large anisotropy of nanorods. Maximum saturation magnetization is obtained for Fe(82) Ni(15) -Pt(3) at 226.6 emu g(-1), whereas maximum coercivity is obtained for Fe(20)Ni(77)-Pt(3) at 136.8 Oe. Shape-dependent reactivity toward the reduction of chlorinated solvents was observed for the FeNi-Pt heterostructured nanomaterials. In particular, the Fe(82)Ni(15)-Pt(3) nanorods are highly reactive in the dechlorination process of 1,1,2,2-tetrachloroethane.     

Preparation and magnetic properties of Cu-ferrite nanorods and nanowires

An aqueous solution method has been developed for preparing Cu-ferrite nanorods (NRs) array and nanowires (NWs) on Cu substrate. The Cu-ferrite NRs exhibit a clear uniaxial anisotropy with the easy axis along rods. The decrease of the reduced remanence from 0.24 in the parallel magnetic field to almost zero in the perpendicular field shows a strong effect of the demagnetizing field perpendicular to the rod axis. The weaker uniaxial anisotropy makes NWs the lower saturation magnetization.     

Synthesis and optical properties of S-doped ZnO nanostructures: nanonails and nanowires

S-doped ZnO nanostructures such as nanonails and nanowires have been synthesized via a simple one-step catalyst-free thermal evaporation process on a large scale. The doping concentration of sulfur into ZnO nanonails and nanowire were 2 atm % and 7.5 atm %, respectively. Studies found that the S-doped ZnO nanonails and nanowires were single-crystalline wurtzite structure and grew along the (001) direction. The average diameters of the nanonails and nanowires were 70 and 50 nm, respectively. Low-temperature photoluminescence spectra of ZnO samples showed two luminescence peaks in the UV and green emission region, respectively. As the concentration of sulfur in the ZnO nanostructures increased, the intensity of the UV emission peak decreased dramatically, and it showed a little blue-shift while the intensity of the green emission increased greatly.     

具有一维梯度直径的金属银纳米线的制备与结构表征

Since the conceptoffunctionally graded m aterials(FG M)is proposed[1,2],m uch attention has been paid toFG M studies.Generally,FG M s were designed with thegradientdistribution ofcom position and structure,andthe graded structure of FG M is achieved by acom position gradient from one side of m aterials to theother,resulting in gradientproperties.Itis well鄄knownthat properties of nanom eter鄄sized m aterials stronglydepend on their sizes.Such size effect offers a newconcept for the design…     

High-quality ultralong Bi2S3 nanowires: structure, growth, and properties

A simple one-step hydrothermal method for large-scale synthesis of ultralong single-crystalline Bi2S3 nanowires was reported, and the nanowires were comprehensively characterized. The diameters of the nanowires are about 60 nm, and their lengths range from tens of microns to several millimeters. The structure of the nanowires was determined to be of the orthorhombic phase, the growth direction was along [001], and the growth mechanism was investigated based on extensive high-resolution transmission electron microscopy observations. Optical absorption experiments revealed that the Bi2S3 nanowires are narrow-band semiconductors with a band gap E(g) approximately 1.33 eV. Electrical transport measurements on individual nanowires gave a resistivity of about 1.2 ohms cm and an emission current of 3.5 microA at a bias field of 35 V/microm. This current corresponds to a current density of about 10(5) A/cm2, which makes the Bi2S3 nanowire a potential candidate for applications in field-emission electronic devices.     

Single crystalline La0.7Sr0.3MnO3 molecular sieve nanowires with high temperature ferromagnetism

Porous mixed-valent manganese oxides are a group of multifunctional materials that can be used as molecular sieves, catalysts, battery materials, and gas sensors. However, material properties and thus activity can vary significantly with different synthesis methods or process conditions, such as temperature and time. Here, we report on a new synthesis route for MnO(2) and LaSr-doped molecular sieve single crystalline nanowires based on a solution chemistry methodology combined with the use of nanoporous polymer templates supported on top of single crystalline substrates. Because of the confined nucleation in high aspect ratio nanopores and of the high temperatures attained, new structures with novel physical properties have been produced. During the calcination process, the nucleation and crystallization of ε-MnO(2) nanoparticles with a new hexagonal structure is promoted. These nanoparticles generated up to 30 μm long and flexible hexagonal nanowires at mild growth temperatures (T(g) = 700 °C) as a consequence of the large crystallographic anisotropy of ε-MnO(2). The nanocrystallites of MnO(2) formed at low temperatures serve as seeds for the growth of La(0.7)Sr(0.3)MnO(3) nanowires at growth temperatures above 800 °C, through the diffusion of La and Sr into the empty 1D-channels of ε-MnO(2). Our particular growth method has allowed the synthesis of single crystalline molecular sieve (LaSr-2 × 4) monoclinic nanowires with composition La(0.7)Sr(0.3)MnO(3) and with ordered arrangement of La(3+) and Sr(2+) cations inside the 1D-channels. These nanowires exhibit ferromagnetic ordering with strongly enhanced Curie temperature (T(c) > 500 K) that probably results from the new crystallographic order and from the mixed valence of manganese.     

Electrospinning preparation, characterization and magnetic properties of cobalt-nickel ferrite (Co(1-x)Ni(x)Fe2)O4) nanofibers

Uniform Co(1-)(x)Ni(x)Fe(2)O(4) (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) nanofibers with average diameter of 110 nm and length up to several millimeters were prepared by calcination of electrospun precursor nanofibers containing polymer and inorganic salts. The as-spun and calcined nanofibers were characterized in detail by TG-DTA, XRD, FE-SEM, TEM, SAED and VSM, respectively. The effect of composition of the nanofibers on the structure and magnetic properties were investigated. The nanofibers are formed through assembling magnetic nanoparticles with poly(vinyl pyrrolidone) as the structure-directing template. The structural characteristics and magnetic properties of the resultant nanofibers vary with chemical composition and can be tuned by adjusting the Co/Ni ratio. Both lattice parameter and particle size decrease gradually with increasing nickel concentration. The saturation magnetization and coercivity lie in the range 29.3-56.4 emu/g and 210-1255 Oe, respectively, and both show a monotonously decreasing behavior with the increase in nickel concentration. Such changes in magnetic properties can mainly be attributed to the lower magnetocrystalline anisotropy and the smaller magnetic moment of Ni(2+) ions compared to Co(2+) ions. Furthermore, the coercivity of Co-Ni ferrite nanofibers is found to be superior to that of the corresponding nanoparticle counterparts, presumably due to their large shape anisotropy. These novel one-dimensional Co-Ni ferrite magnetic nanofibers can potentially be used in micro-/nanoelectronic devices, microwave absorbers and sensing devices.     

Highly efficient dye-sensitized solar cells with a titania thin-film electrode composed of a network structure of single-crystal-like TiO2 nanowires made by the "oriented attachment" mechanism

In this study, single-crystal-like anatase TiO(2) nanowires were formed in a network structure by surfactant-assisted self-assembling processes at low temperature. The crystal lattice planes of the nanowires and networks of such wires composed of many nanoparticles were almost perfectly aligned with each other due to the "oriented attachment" mechanism, resulting in the high rate of electron transfer through the TiO(2) nanonetwork with single-crystal-like anatase nanowires. The direction of crystal growth of oriented attachment was controlled by changing the mole ratio of acetylacetone to Ti, that is, regulating both the adsorption of surfactant molecules via control of the reaction rate and the surface energy. A single-crystalline anatase exposing mainly the [101] plane has been prepared, which adsorbed ruthenium dye over 4 times higher as compared to P-25. A high light-to-electricity conversion yield of 9.3% was achieved by applying the titania nanomaterials with network structure as the titania thin film of dye-sensitized solar cells.     

Synthesis of uniform CdS nanowires in high yield and its single nanowire electrical property

Large-scale high quality CdS nanowires with uniform diameter were synthesized by using a rapid and simple solvothermal route. Field emission scan electron microscopy (FESEM) and transmission electron microscopy (TEM) images show that the CdS nanowires have diameter of about 26 nm and length up to several micrometres. High resolution TEM (HRTEM) study indicates the single-crystalline nature of CdS nanowires with an oriented growth along the c-axis direction. The optical properties of the products were characterized by UV-vis absorption spectra, photoluminescence spectra and Raman spectra. The resistivity, electron concentration and electron mobility of single NW are calculated by fitting the symmetric I-V curves measured on single NW by the metal-semiconductor-metal model based on thermionic field emission theory.     

Sol-gel template synthesis and photoluminescence of n- and p-type semiconductor oxide nanowires.

A sol-gel template technique has been put forward to synthesize single-crystalline semiconductor oxide nanowires, such as n-type SnO2 and p-type NiO. Scanning electron microscopy and transmission electron microscopy observations show that the oxide nanowires are single-crystal with average diameters in the range of 100-300 nm and lengths of over 10 microm. Photoluminescence (PL) spectra show a PL emission peak at 401 nm for n-type semiconductor SnO2, and a PL emission at 407 nm for p-type semiconductor NiO nanowires, respectively. Correspondingly, the observed violet-light emission at room temperature is attributed to near-band-edge emission for SnO2 nanowires and the 3d(7)4s-->3d8 transition of Ni2+ for NiO nanowires.