Template-free synthesis of nickel nanowires by magnetic field

Nickel nanowires were prepared by a template free method combined with chemical reduction and magnetic field. The application of an external magnetic field resulted in the formation of self-aligned metallic nickel nanowires of about 50 nm in diameter. Nickel particles were prepared in the absence of a magnetic field to better illustrate the structure directing role of the magnetic field. Physical properties of the nickel nanochains were examined by scanning electron microscopy (SEM), transmission electron microscope (TEM), X-Ray diffraction (XRD), and thermogravimetric analysis (TGA) methods. This study provides a simple method to prepare Ni nanowires in large scale which broads their practical applications.     

不同结构镍纳米线阵列的制备及其磁性

采用直流电沉积在多孔有序氧化铝模板中制备了不同结构的有序镍纳米线阵列。采用SEM和TEM对所制备的镍纳米线的形貌和结构进行了表征。研究了镍纳米线不同结构对镍纳米线阵列磁性性能的影响规律．当电沉积电压为2．5V时制备的镍纳米线为多晶结构；电沉积电压4V时，镍纳米线为沿[220]择优取向的单晶结构；电沉积电压＞5V时，择优取向由[220]转为[111]方向．磁滞回线结果表明，单晶镍纳米线阵列与多晶纳米线阵列相比具有更高的矩形度，沿[111]择优取向的单晶纳米线相比沿[220]取向的单晶镍纳米线具有更大的矩形度，表现出显著的磁各向异性。     

垂直铜基底钴纳米片阵列的电化学制备及磁性能研究

以柠檬酸氢二铵作为包裹剂,采用一步恒流电沉积法在铜基体上制备出垂直生长的钴纳米片阵列,并采用SEM、XRD及EDX对该产物的形貌、晶体结构以及化学成分进行表征。研究结果显示,包裹剂种类、浓度以及电沉积时间对钴纳米片阵列的形貌具有重要影响。此外,钴纳米片阵列因其特殊的三维结构表现出优异的磁各向异性特征,其中易磁化轴平行于基底方向,而在垂直于基底方向上则具有较好的铁磁性能。     

Metallic cobalt microcrystals with flowerlike architectures: Synthesis, growth mechanism and magnetic properties

Well-defined, three-dimensional (3D) flowerlike metallic Co microcrystals with several radiating hexagonal-tapered petals assembled by particles size of 150-250 nm were fabricated via a facile hydrothermal reduction route under a fixed basic condition. The morphology and structure of the products were characterized by scanning electronic microscopy (SEM), energy-dispersive X-ray (EDX), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS) and powder X-ray diffraction (XRD). The probable formation mechanism of the flowerlike Co microcrystals was discussed based on the experimental results. Magnetic properties of Co microcrystals were investigated by a commercial Physical Properties Measurement System (PPMS). The flowerlike products exhibited ferromagnetic characteristics with a saturation magnetization of 128.1 emu/g and a coercivity of 232.5 Oe at room temperature. Compared to the coercivity value of bulk Co, the products displayed a remarkable enhanced value due to their special morphology.     

Optical and magnetic properties of 30 and 60 nm Ni nanowires

Ni nanowire arrays of high aspect ratio with the diameters of about 30 nm and 60 nm were prepared by DC applied AC electrodeposition. We observe the different preferred orientation and various magnetic behaviors of 30 and 60 nm diameter nanowires. In addition, the coercivity H_c(||), squareness S(||) and the ratio H_c(||)/H_c(⊥) where the applied field is parallel (||) and perpendicular (⊥) to the long axis of nanowires increase with decreasing wire diameter. This is the first time that optical results of Ni nanowires were presented.     

Structure and magnetic properties of hierarchical cobalt dendrites

Hierarchical cobalt dendrites with ferromagnetic properties have been synthesized by using the in situ produced cobalt carbonate together with cobalt oxalate as precursor and hypophosphite (H₂PO₂⁻) as the reducing agent in mixed solutions at 160 °C. XRD and SAED patterns reveal that the as-prepared cobalt dendrites have a single-crystalline structure with a [001] growth orientation. The shape evolution of the hierarchical cobalt dendrites was investigated.     

Preparation and growth mechanism of nickel nanowires under applied magnetic field

Nano-Micro Letters - Nickel nanowires with large aspect ratio of up to 300 have been prepared by a hydrazine hydrate reduction method under applied magnetic field. The diameter of nickel nanowires...     

Enhanced magnetic properties of cobalt nanoparticles on FeMn films

Monodisperse cobalt nanoparticles are synthesized by the thermal decomposition of Co₂(CO)₈ in phenyl ether and subsequently deposited on antiferromagnetic (AFM) FeMn films and glass substrates, respectively. Magnetic measurement shows that the as-prepared Co nanoparticles are superparamagnetic and can be transformed into ferromagnetic (FM) through thermal treatment. While keeping monodisperse, the annealed FM Co nanoparticles on AFM FeMn films show a much larger coercivity than the ones on glass substrates due to FM/AFM exchange coupling. Accordingly, we propose a convenient method to enhance magnetic properties of nanoparticles.     

In situ synthesis of graphene/cobalt nanocomposites and their magnetic properties

Graphene, which possesses unique nanostructure and excellent properties, is considered as a low cost alternative to carbon nanotubes in nanocomposites. In this study, we present a simple in situ approach for the deposition of cobalt (Co) nanoparticles onto surfaces of graphene sheets by hydrazine hydrate reduction. The as-synthesized composites were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM) and thermogravimetry and differential scanning calorimetry. It was shown that the as-formed Co nanoparticles were densely and homogeneously deposited on the surfaces of the graphene sheets and as a result, the restacking of the as-reduced graphene sheets was effectively inhibited. Magnetic studies reveal that the graphene/Co nanocomposite displays ferromagnetic behavior with saturation magnetizations of 53.4 emu g⁻¹, remanent magnetization of 6.0 emu g⁻¹ and coercivity of 226 Oe at room temperature, which make it promising for practical applications in future nanotechnology.     

Magnetic behavior of arrays of nickel nanowires: Effect of microstructure and aspect ratio

Arrays of nickel nanowires with aspect ratio of ∼1200 and diameters ranging between 25 and 100 nm have been fabricated by electrodeposition in etched ion track templates. Samples with different areal densities ranging from 1 × 10⁶ cm⁻² to 1 × 10⁸ cm⁻² have been prepared for this study. Magnetic measurements were performed at room temperature for different aspect ratios and diameters of the wires. Coercivity of the wires showed a strong dependence on aspect ratio (l/d), diameter and microstructure. In the case of parallel applied field coercivity of the wires has maximum value at ∼40 nm diameter. The wires with high areal densities showed relatively lower coercivities as compared to the low density samples. The results have been discussed by taking into account various magnetic anisotropies originating from the shape and crystalline nature of the wires, and the magnetostatic interactions among the wires.     

Flower-like hierarchical nickel microstructures: Facile synthesis,growth mechanism,and their magnetic properties

Flower-like hierarchical nickel microstructures were prepared by a facile chemical reduction method requiring 4 h at temperature of 85 °C without any template or external magnetic field. Nickel (II) sulfate hexahydrate was used as nickel source and hydrazine hydrate acted as the reducing agent. XRD study confirmed the highly crystalline with face-centered cubic (fcc) phase. SEM images revealed that the individual flower-like microstructures have an average diameter of 1–2 μm and are composed of sword-like nanopetals growing radially from the core of the spherical particles. HRTEM image and SAED pattern of the single petal show that the lattice spacing is 0.203 nm corresponding to the (1 1 1) plane of fcc nickel and the growth orientation is along [0 1 1] direction. A rational formation process of nickel micro-flowers was proposed. Magnetic hysteresis measurements revealed that the hierarchical nickel microstructures possess ferromagnetic behavior with an enhanced coercivity value of about 203.3 Oe.     

Structure, growth and magnetic property of hard magnetic CoPtP nanowires synthesized by electrochemical deposition

This paper reports the electrochemical synthesis and characterization of one dimensional hard magnetic CoPtP nanowires. Three electrode potentiostatic electrochemical technique was used to deposit nanowires into a nanoporous track-etched polycarbonate membrane with a nominal pore diameter 50 nm and thickness around 6-9 μm. The room temperature electrolyte used for the deposition of nanowires consists of 60 g/lt CoSO₄7H₂O, 4.1 g/lt H₂PtCl₆, 4.5 g/lt NaHPO₂ and 25 g/lt B(OH)₃. The structural morphology was observed by scanning electron microscope and transmission electron microscope. The magnetic property of the nanowires was measured by vibrating sample magnetometer before removing the template. The coercive fields were measured to be 143 kA m^− 1 and 103 kA m^− 1 for parallel (H_║) and perpendicular to the nanowire axis, respectively. The higher coercivity value for H_║ indicating nanowires' easy magnetization direction lies along the nanowires' axis. The average composition of the CoPtP nanowires was determined by electron dispersive spectroscopy and the crystallinity was measured by X-ray diffractometer.     

Morphology-controlled fabrication and magnetic properties of nickel assemblies

In this study, nickel assemblies with various morphologies, including nanospheres, pinecone structures, microspheres, and necklace chains, were synthesized in ethylene glycol solution by adjusting the experimental conditions. We propose a possible growth mechanism for the formation of different structures, which involves the rapid nucleation of primary particles followed by slow aggregation and Ostwald ripening crystallization of the primary particles. The saturation magnetization (M_s) of the nickel assemblies decreased as the particle size declined. We found that the coercivity (H_c) of the necklace chains appeared to be higher than that of other structures due to their shape anisotropy. The results of our study indicated that the magnetic properties of the nickel assemblies were morphology-dependent. The coercivities of the nickel samples with different structures prepared in this study were two orders of magnitude higher than that of bulk nickel (0.7 Oe).     

Facile synthesis and magnetic properties of manganese dioxide nanowires

A large number of MnO₂ nanowires were fabricated by a facile hydrothermal method. The nanowires have a tetragonal pyrolusite structure and a smooth surface. The common bulk defects such as dislocations, twinnings and stacking faults are not detected by HRTEM measurement. The magnetisation dependence of temperature indicates that the magnetisation, linearly and monotonically, increases with decreasing temperature in the range 300–80?K, revealing the paramagnetic properties of the nanowires. The first discharge capacity reaches 223.5?mA?h?g^?1, and the value of capacity steadily decreases during the following cycles, down to an acceptable 122.3?mA?h?g^?1 after 25 cycles. The high surface ratio of nanowires is the main reason for the excellent discharge cycle property of the MnO₂ nanowires.     

水热合成法制备La0.7Sr0.3FeO3纳米线的合成机理研究

在表面活性剂CTAB水溶液中添加硝酸盐溶液,并滴加氨水,采用水热合成法在180℃的温度下反应9h,制备了La0.7Sr0.3FeO3前驱体,在700℃下煅烧6h后得到La0.7Sr0.3FeO3纳米颗粒组装的纳米线。利用SEM、TEM和XRD对其形貌、尺寸和结构等进行了表征。制备的La0.7Sr0.3FeO3纳米线是由约为20nm的纳米颗粒组装而成的,纳米线的最大长径比达100以上。通过改变水热合成时间和前驱体的煅烧温度等实验条件,对La0.7Sr0.3FeO3纳米线的物相转化和生长机理进行了分析。表面活性剂CTAB作为生长控制剂和颗粒凝聚载体,能够控制材料沿着轴向生长,形成纳米线。     

Co88Ni12合金纳米线阵列的制备与磁性能表征

采用直流电化学沉积方法，在多孔阳极氧化铝模板的纳米级微孔内电沉积钴镍合金，制备出直径为30nm，长度为几个微米的准一维合金纳米线（阵列）材料；随后采用场发射扫描电子显微镜（FE-SEM），透射电子显微镜（TEM），X射线衍射仪（XRD），振动样品磁强计（VSM）对纳米线的形貌、结构及其磁性能进行了相关表征与测试．发现所制备的Co88Ni12合金纳米线表面光滑，粗细均一，具有较高的长径比；呈现密排六方结构（hcp），沿[100]择优取向生长，易磁化方向沿纳米线轴向方向．     

Synthesis and magnetic properties of shuriken-like nickel nanoparticles

Shuriken-like nickel nanoparticles were successfully synthesized by a thermal decomposition method at 200 °C with Nickel(II) acetylacetonate (Ni(acac)₂) as the precursor and oleylamine (OAm) as the solvent and reductant, respectively. The phase structures, morphologies and sizes, and magnetic properties of the as-synthesized nickel products were characterized in detail by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometer (VSM). Some key reaction parameters, such as the reaction time, reaction temperature and surfactants, have important influence on the morphology of the final products. XRD pattern indicated that the products are well-crystallized face-centered cubic (fcc) nickel phase. SEM images demonstrated that the nickel nanoparticles are shuriken-like morphology with average size around 150 nm. The mechanism of shuriken-like Ni nanoparticles (NPs) is proposed. The magnetic hysteresis loops of shuriken-like and spherical nickel products illustrated the ferromagnetic nature at 300 K, indicating its potential applications in magnetic storage.     

Fe0.3Co0.7纳米有序阵列的制备和磁性

使用小孔径阳极氧化铝模板制备Fe0.3Co0.7纳米线有序阵列,研究了热处理对其磁性的影响.结果表明,热处理对Fe0.3Co0.7纳米线有序阵列的结晶度和局部形状各向异性有重大的影响,导致纳米阵列的矫顽力和剩磁比发生相应的变化.在适当热处理条件下获得的Fe0.3Co0.7纳米线有序阵列具有较高的矫顽力和剩磁比.在H2保护下550℃处理时获得最高的矫顽力2.63×105 A/m,矫顽力随着热处理时间的增加先是快速增加,然后趋向平缓,最后有一定程度的下降.     

氨气流量对GaN纳米线生长及性能的影响

利用磁控溅射技术在Si衬底上沉积Ga2O3/Co薄膜,然后在不同氨气流量下于950℃退火15min。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、傅立叶红外吸收(FTIR)光谱、高分辨透射电子显微镜(HRTEM)和光致发光谱(PL)对样品进行了分析表征。结果表明,氨气流量对GaN纳米线的生长及性能有很大影响。简单讨论了GaN纳米线的生长机理。     

Effect of Sb doping on the opto-electronic properties of SnO2 nanowires

Antimony (Sb) doping of SnO₂ nanowires (NWs) was investigated for its optical and electrical effects. The low-temperature photoluminescence spectra of SnO₂ NWs varied significantly with increasing Sb content, where the temperature-dependence of the visible emission at ca. 400 nm was distinctive with Sb-doping, indicating different defect states, such as neutral and positively charged oxygen vacancies. Field effect transistors (FETs) with low-level Sb-doped SnO₂ NW channels exhibited higher mobility, charge concentration, and faster response and recovery to UV light than intrinsic SnO₂ NW FETs.