Length-controlled synthesis of oriented single-crystal rutile TiO2 nanowire arrays

A free-standing, large area, oriented single-crystal rutile TiO(2) nanowire arrays with a controlled length in the range of 10-80 μm are prepared via a facile one-step synthesis. The growth process is studied systematically in an appropriate amount of H(2)O(2) and HCl solution under hydrothermal conditions. The length of the nanowires can be easily tuned by varying the experimental parameters, including reaction temperature and reaction time. High-resolution transmission electron microscopy demonstrated that the nanowires have single-crystal structure. Furthermore, the photoluminescence characteristics and photocatalytic properties of oriented single-crystal rutile TiO(2) nanowires was discussed in this paper, respectively. It is found that the increased reaction temperature is helpful to photocatalytic reactivity and photoluminescence properties.     

钴纳米线的模板制备与磁性

利用二次阳极氧化法制备了多孔阳极氧化铝模板. 用直流电化学沉积方法成功地在模板孔道内制备了钴纳米线. 采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)和振动样品磁强计(VSM)对样品的形貌、晶体结构和磁性进行了研究. 结果表明， 模板的孔径均匀, 孔道平直. 钴纳米线为多晶的六方密堆积结构. 钴纳米线具有明显的磁各向异性, 这主要起源于纳米线的形状各向异性.     

氧化铝模板中Ag纳米线阵列的选择性生长

利用Ag离子与Br离子之间的化学沉积作用在孔隙中充满明胶的阳极氧化铝(AAO)模板中制备了AgBr/AAO纳米介孔复合材料.材料选择性曝光后,利用原位显影液对其进行化学显影,在AAO模板中选择性得到Ag纳米线阵列.实验结果表明:Ag纳米线是连续的、致密的,且具有多晶结构,充满了曝光部分的模板孔隙.本文还对影响Ag纳米线选择性生长的因素进行了简单讨论.     

Preparation and characterization of straight and zigzag AlN nanowires

Hexagonal single-crystal AlN nanowires with straight or zigzag morphologies were successfully synthesized by the reaction of aluminum alloy in an ammonia/nitrogen atmosphere at 1100 degrees C. It is found that the crystal tropism of the nanowires is along [0001], whereas the growth directions of the zigzag nanowires shift between [2111] and [2111].     

Phase separations of single-crystal nanowires grown by self-catalytic chemical vapor deposition method

The fundamentals of phase separations of single-crystal III-V nitride nanowires grown by self-catalytic chemical vapor deposition method have been studied. Experimental tools, such as high resolution transmission electron microscopy and scanning electron microscopy, have been used to characterize the nanowires. The study indicates that nanowires with diameters exceeding about 100 nm undergo phase transitions and/or crystal structure deterioration. The study highlights a relationship between the crystal structure and the kinetics of growth of nanowires.     

Self-catalysis: a contamination-free, substrate-free growth mechanism for single-crystal nanowire and nanotube growth by chemical vapor deposition

A unified mechanism for the growth of a wide variety of long, uniform, single-crystal nanowires and whiskers, including III-V and II-VI binary, ternary, and quaternary nanowires and whiskers, without the use of any substrate and catalyst has been presented. While elucidating the mechanism, attempts have been made to provide a kinetic and thermodynamic rationale for the growth. Various features of the growth mechanism, including the formation of liquid droplets and seeds, nucleation, and creation of products, have been discussed. Extensive studies of illustrative examples provide the validity of the proposed mechanism. The influence of various parameters such as growth temperature and chamber pressure on the growth mechanism has been studied. The advantages and disadvantages of the proposed mechanism, and its superiority to the well-known vapor-liquid-solid mechanism, have been elucidated. Means to improve the mechanism to obtain self-aligned nanowires and whiskers have been suggested. Based on these, it has been demonstrated that the present mechanism is indeed a powerful self-catalytic growth mechanism uniquely suited to the growth of a wide variety of single-crystal nanowires and whiskers. It can be very useful also for the growth of single-crystal nanotubes.     

银纳米线的TEM表征

通过交流电沉积的方法,以多孔铝阳极氧化膜（Al2O3/Al）为模板,制备金属银纳米线.透射电子显微镜（TEM）分析表明, 银纳米线长度平均约为5 μm, 直径25 nm；银纳米线在多孔Al2O3/Al孔内互相平行,显示凸凹相间的条纹结构.选区电子衍射（SAED）证实,银纳米线具有面心立方（FCC）的多晶结构,探讨了银纳米线凸凹相间条纹结构的形成机理.     

Template-grown metal nanowires

The growth of metal nanowires using membranes as hard templates is reviewed. The method provides access to arrays of single-crystal metal nanowires and to quasi-one-dimensional metal nanostructures with controlled compositional variation along their length. Recent applications of these kinds of nanowires to problems in superconductivity, optical spectroscopy and sensing, and catalytic conversion of chemical to mechanical energy are reviewed.     

Metallic single-crystal CoSi nanowires via chemical vapor deposition of single-source precursor

We report the synthesis, structural characterization, and electrical transport properties of free-standing single-crystal CoSi nanowires synthesized via a single-source precursor route. Nanowires with diameters of 10-150 nm and lengths of greater than 10 mum were synthesized through the chemical vapor deposition of Co(SiCl(3))(CO)(4) onto silicon substrates that were covered with 1-2 nm thick SiO(2). Transmission electron microscopy confirms the single-crystal structure of the cubic CoSi. X-ray absorption and emission spectroscopy confirm the chemical identity and show the expected metallic nature of CoSi, which is further verified by room-temperature and low-temperature electrical transport measurements of nanowire devices. The average resistivity of CoSi nanowires is found to be about 510 muOmega cm. Our general and rational nanowire synthesis approach will lead to a broad class of silicide nanowires, including those metallic materials that serve as high-quality building blocks for nanoelectronics and magnetic semiconducting Fe(1-x)Co(x)Si suitable for silicon-based spintronics.     

Synthesis and characterization of dimensionally ordered semiconductor nanowires within mesoporous silica.

Semiconductor nanowires of silicon have been synthesized within the pores of mesoporous silica using a novel supercritical fluid solution-phase approach. Mesoporous silica, formed by the hydrolysis of tetramethoxysilane (TMOS) in the presence of a triblock copolymer surfactant, was employed for the nucleation and growth of quantum-confined nanowires. The filling of the silica mesopores with crystalline silicon and the anchoring of these nanowires to the sides of the pores were confirmed by several techniques including electron microscopy, powder X-ray diffraction, 29Si magic angle spinning nuclear magnetic resonance, infrared spectroscopy, and X-ray fluorescence. Effectively, the silica matrix provides a means of producing a high density of stable, well-ordered arrays of semiconductor nanowires in a low dielectric medium. The ordered arrays of silicon nanowires also exhibited discrete electronic and photoluminescence transitions that could be exploited in a number of applications, including nanodevices and interconnects.     

Self-supported particle-track-etched polycarbonate membranes as templates for cylindrical polypyrrole nanotubes and nanowires: an X-ray scattering and scanning force microscopy investigation

Self-supported particle-track-etched polycarbonate membranes with nearly perfect cylindrical pores are used for the preparation of similarly perfect cylindrical polypyrrole nanowires and nanotubes. A complete investigation of the structural properties that result at different stages of the preparation route of polypyrrole nanowires and nanotubes is based on a combination of real and reciprocal space techniques. Nanoporous membranes with nominal pore size ranging from 5 to 150 nm and pore density up to 10(9) pores/cm(2) made from 21-microm-thick polycarbonate films are used. Polypyrrole nanotubes or nanowires are synthesized inside the pores. A real-space picture of the nanomaterial results from scanning force microscopy (SFM) on ultrathin sections made in two directions to obtain structures in the sample surface as well as perpendicular to the surface. From a model-based fit to the small-angle and ultra-small-angle X-ray scattering (SAXS/USAXS) data, the geometric pore structure is obtained and compared to values determined with scanning electron microscopy (SEM). Nanopores, nanowires, and nanotubes are described by uniform solid cylinders or hollow tubes, which are oriented highly parallel to each other and exhibit a small size distribution. Below a critical pore diameter, solid nanowires are produced whereas above this limit hollow nanotubes result.     

Effective deposition potential induced size-dependent orientation growth of Bi-Sb alloy nanowire arrays

The influence of effective deposition potential on the orientation and diameter of Bi(1-x)Sbx alloy nanowire arrays by pulsed electrodeposition technique was reported. X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy analysis show that the orientation of the Bi(1-x)Sbx nanowires can be turned from the [110] to the [202] direction by increasing the effective deposition potential, and the nanowires fully fill in the pores of the AAM in the lower potential region, while in the higher potential region the nanowires partly fill the pores of the AAM. The origin of those phenomena and the growth mechanism of the nanowire are discussed together with composition analysis.     

Synthesis of CdS and ZnS nanowires using single-source molecular precursors

Single-source molecular precursors were used to synthesize II-VI compound semiconductor nanowires for the first time. Cadmium sulfide and zinc sulfide nanowires were prepared using cadmium diethyldithiocarbamate, Cd(S2CNEt2)2, and zinc diethyldithiocarbamate, Zn(S2CNEt2)2, respectively, as precursors in a gold nanocluster-catalyzed vapor-liquid-solid growth process. High-resolution transmission electron microscopy studies show that the CdS and ZnS nanowires are single-crystal wurtzite structures with stoichiometric compositions. In addition, photoluminescence measurements demonstrate that these nanowires exhibit high-quality optical properties. The applicability of our approach to the synthesis of other compound and alloy semiconductors nanowires as well as nanowire heterostructures of these materials is discussed.     

Densely packed single-crystal Bi2Fe4O9 nanowires fabricated from a template-induced sol-gel route

Densely packed single-crystal Bi₂Fe₄O₉ nanowires were successfully synthesized by a template-induced citrate-based sol-gel process. The structural properties of the nanowires were characterized using many techniques. The results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that Bi₂Fe₄O₉ nanowires possessed a uniform length and diameter, which were controlled by the thickness and the pore diameter of the applied porous anodic aluminum oxide (AAO) template, respectively. The results of X-ray diffraction (XRD) and the selected area electron diffraction (SAED) indicated that Bi₂Fe₄O₉ nanowires had an orthorhombic single-crystal structure. Furthermore, the energy-dispersive X-ray (EDX) spectroscopy demonstrated that the stoichiometric Bi₂Fe₄O₉ was formed. The possible formation mechanism of nanowires was also discussed.     

Temperature dependence of the field effect mobility of solution-grown germanium nanowires

The temperature dependence of the field effect mobility was measured for solution-grown single-crystal Ge nanowires. The nanowires were synthesized in hexane from diphenylgermane by the supercritical fluid-liquid-solid process using gold nanocrystals as seeds. The nanowires were chemically treated with isoprene to passivate their surfaces. The electrical properties of individual nanowires were then measured by depositing them on a Si substrate, followed by electrical connection with Pt wires using focused ion beam assisted chemical vapor deposition. The nanowires were positioned over TaN or Au electrodes covered with ZrO2 dielectric that were used as gates to apply external potentials to modulate the conductance. Negative gate potentials increased the Ge nanowire conductance, characteristic of a p-type semiconductor. The temperature-dependent source/drain current-voltage measurements under applied gate potential revealed that the field effect mobility increased with increasing temperature, indicating that the carrier mobility through the nanowire is probably dominated either by a hopping mechanism or by trapped charges in fast surface states.     

Increase of the photoluminescence intensity of InP nanowires by photoassisted surface passivation

As-grown single-crystal InP nanowires, covered with a surface oxide, show a photoluminescence efficiency that strongly varies from wire to wire. We show that the luminescence efficiency of single-crystal InP nanowires can be improved by photoassisted wet chemical etching in a butanol solution containing HF and the indium-coordinating ligand trioctylphosphine oxide. Electron-hole photogeneration, electron scavenging, and oxidative dissolution combined with surface passivation by the indium-coordinating ligand are essential elements to improve the luminescence efficiency. Time traces of the luminescence of surface-passivated wires show strong oscillations resembling the on-off blinking observed with single quantum dots. These results reflect the strong influence of a single or a few nonradiative recombination center(s) on the luminescence properties of an entire wire.     

Chemical surface passivation of Ge nanowires

Surface oxidation and chemical passivation of single-crystal Ge nanowires with diameters ranging between 7 and 25 nm were studied. The surface chemistry differs significantly from that of well-studied monolithic atomically smooth single-crystal substrates. High-resolution Ge 3d XPS measurements reveal that Ge nanowires with chemically untreated surfaces exhibit greater susceptibility to oxidation than monolithic Ge substrates. Multiple solution-phase routes to Ge nanowire surface passivation were studied, including sulfidation, hydride and chloride termination, and organic monolayer passivation. Etching in HCl results in chloride-terminated surfaces, whereas HF etching leads to hydride termination with limited stability. Exposure to aqueous ammonium sulfide solutions leads to a thick glassy germanium sulfide layer. Thermally initiated hydrogermylation reactions with alkenes produce chemically stable, covalently bonded organic monolayer coatings that enable ohmic electrical contacts to be made to the nanowires.     

Single-crystalline, size, and orientation controllable nanowires and ultralong microwires of organic semiconductor with strong photoswitching property

Single-crystalline, precise size-controlled nanowires and ultralong microwires with lengths reaching several millimeters of organic semiconductor 1 were prepared in large scale by cast assembly. The size and density of the nanowires and microwires could be controlled by simply adjusting the concentration of 1 in casting solutions. More importantly, the formation of these nanowires and microwires showed no substrate and solvent dependence and was orientation controllable. Highly reproducible and sensitive photo response characteristics were observed in these nanowires and microwires. Fast and reversible photoswitchers based on multiple or individual single-crystal microwires were fabricated via "multi times gold wire mask moving" technique with switch ratio over 100.     

化学修饰阳极氧化铝模板法合成小尺寸聚苯胺纳米线

利用表面活性剂对阳极氧化铝(AAO)模板进行化学修饰，发展了模板合成法，从而得到更小尺寸的聚苯胺纳米管、线.在表面活性剂十八烷基脂肪酸(R18)修饰下，在14 nm孔径的AAO模板中合成7 nm的纳米线.对不同表面活性剂的比较后发现,通过改变修饰表面活性剂上烷基链长可以对所制备的聚合物纳米管、线的直径进行调控.     

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.