Preparation of well-aligned carbon nanotubes/silicon nanowires core-sheath composite structure arrays in porous anodic aluminum oxide templates

The well-aligned carbon nanotubes (CNTs) arrays with opened ends were prepared in ordered pores of anodic aluminum oxide (AAO) template by the chemical vapor deposition (CVD) method. After then, silicon nanowires (SiNWs) were deposited in the hollow cavities of CNTs. By using this method, CNTs/SiNWs core-sheath composite structure arrays were synthesized successfully. Growing structures and physical properties of the CNTs/SiNWs composite structure arrays were analyzed and researched by the scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction spectrum (XRD), respectively. The field emission (FE) behavior of the CNTs/SiNWs composite structure arrays was studied based on Fowler-Nordheim tunneling mechanism and current-voltage (/-V) curve. And the photoluminescence (PL) was also characterized. Significantly, the CNTs/SiNWs core-sheath composite structure nanowire fabricated by AAO template method is characteristic of a metal/semiconductor (M/S) behavior and can be     

Formation mechanism of Si3N4 nanowires via carbothermal reduction of carbonaceous silica xerogels

Si3N4 nanowires prepared from the carbothermal reduction of carbonaceous silica xerogels with metal salt additives usually contain a small amount of nanotubes. This paper is devoted to the investigation of the formation mechanism of the Si3N4 nanowires. As-prepared samples heated at 1300 degrees C for different reaction times (1, 5, 10, and 30 h) were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results showed that all the samples mainly consisted of nanowires, while their crystalline phases changed with the heating time. Nitrogen-doped silicon oxide nanowires were first produced via the vapor-liquid-solid process and then underwent a stepwise surface nitrogenization to silicon nitride. The suggested mechanism can easily explain the existence of nanotubes in the Si3N4 nanowires.     

铅纳米线阵列的制备

使用电化学沉积方法,在有序的氧化铝模板(AAO)孔洞中制备了铅纳米线有序阵列。用X射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)对样品的结构、形貌、进行表征和观测。XRD的结果表明所制备的样品为纯的立方面心铅,且纳米线生长沿<220>有很好的取向。FE-SEM的图片清晰地说明铅纳米线阵列是大面积、高填充率和高度有序的。TEM的结果显示纳米线直径均匀、表面光滑且长径比大。     

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.     

氧化铁纳米线阵列的溶胶-凝胶模板法制备与表征

0引言氧化铁在颜料、磁记录材料和催化剂等方面具有广泛的应用[1,2]。尤其是纳米氧化铁在纳米尺度具有良好的气敏特性[3]。纳米材料可以分为零维、一维、二维纳米材料,一维材料是纳米材料的重要组成部分,是纳米组装的基础。一维纳米材料的制备方法中氧化铝模板法占有极其重要的     

Silicon-silica nanowires, nanotubes, and biaxial nanowires: inside, outside, and side-by-side growth of silicon versus silica on zeolite

It was demonstrated that zeolite can be used as a pseudo-template to grow very fine and uniform silicon nanostructures via disproportionation reaction of SiO by thermal evaporation. Three distinct types of composite nanowires and nanotubes of silicon and silica were grown on the surfaces of zeolite Y pellets. The first type is formed by an ultrafine crystalline silicon nanowire sheathed by an amorphous silica tube (a silicon nanowire inside a silica nanotube). The second type is formed by a crystalline silicon nanotube filled with amorphous silica (a silicon nanotube outside a silica nanowire). The third type is a biaxial silicon-silica nanowire structure with side-by-side growth of crystalline silicon and amorphous silica. These silicon nanostructures exhibit unusually intense photoluminescence (in comparison to ordinary silicon nanowires).     

大面积Bi单晶纳米线阵列的制备

在有序的氧化铝模板(AAO)的孔洞中, 采用电化学沉积工艺成功地制备了准金属Bi纳米线有序阵列. 使用X射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)及高分辨电子显微镜(HRTEM)对样品的结构和形貌进行了表征. XRD结果表明, 所制备的铋样品为六方相, 且沿[110]方向有很好的生长取向; FE-SEM图片清晰地说明铋纳米线阵列是大面积、填充率高和高度有序的; TEM的结果显示纳米线直径均匀、表面光滑且长径比大; HRTEM图片中清晰的晶格条纹和选区电子衍射(SAED)结果表明纳米线是单晶.     

化学气相沉积法制备Sn2S3一维纳米结构阵列

运用化学气相沉积法(CVD), 直接以Sn和S为原料分区加热蒸发, 通过控制温度分布、气压、载气流量和金属铅纳米颗粒分布等宏观实验条件, 成功制备大面积Sn₂S₃一维纳米结构阵列. 扫描电子显微镜(SEM)图片显示: Sn₂S₃一维纳米结构的横向尺度在100 nm左右, 长约几个微米. X射线衍射（XRD）谱显示: 所制备样品的晶体结构属于正交晶系, 沿[002]方向生长. 紫外-可见漫反射谱表明Sn₂S₃一维纳米结构是带隙为2.0 eV的直接带隙半导体. 讨论了温度分布和金属铅纳米颗粒对Sn₂S₃一维纳米结构生长的影响, 并指出其生长可能遵循气-固(V-S)生长机理.     

Melting of indium,tin, and zinc nanowires embedded in the pores of anodic aluminum oxide

The melting temperature of metal nanostructures embedded in the matrix is an essential thermodynamic characteristic and a key parameter of the processes of their transformation into semiconductor structures. In this work, great attention is paid to the investigation of the behavior of one-dimensional metal nanocrystals near the melting point. For this purpose, the arrays of In, Sn, and Zn nanowires with different diameters have been electrochemically grown in the pores of anodic aluminum oxide (AAO), which is confirmed by the results of the microscopy and the phase X-ray diffraction analysis. The melting of nanowire arrays with different diameters has been investigated by means of differential scanning calorimetry (DSC). Aside from the expected melting temperature decrease, with decreasing the diameter of nanowires, it has been established that the melting peaks of nanostructure arrays have a complex shape that requires detailed elaboration in order to more accurately define the melting temperature. It is shown that the signal waveform while melting depends on geometric parameters of the structure, and the peak being mapped onto the DSC curve is the result of superposition of the melting peaks of nanowires with several characteristic dimensions. For the arrays of In, Sn, and Zn nanowires in AAO, there have been defined the melting temperature values according to the methodology offered, and there has been presented the dependence of the melting temperature decrease on the nanowires' diameter.     

Controlled growth of mesostructured crystalline iron oxide nanowires and Fe-filled carbon nanotube arrays templated by mesoporous silica SBA-16 film

The three-dimensional (3D) accessible pore structures (Imm space groups) of continuous mesoporous silica SBA-16 thin films have been prepared by a dip-coating technique in nonaqueous media under acidic conditions on indium-tin oxide glass (ITO). The films are oriented with the (111) crystal plane perpendicular to the surface of the film. On one hand, deposition of iron metal into the mesopores of SBA-16 films was achieved by using an electrochemical method. The Fe2O3 nanowire arrays were synthesized. The crystalline structures of porous Fe2O3 nanowires and nanorods were studied via TEM, SEM, and XRD. On the other hand, a small amount of Fe was deposited into the pores of the SBA-16 thin film as a catalyst, and carbon nanotube arrays formed inside the pores of SBA-16 film were fabricated by catalytic decomposition of acetylene at 700 degrees C. The second-order template synthesis method for preparing the ordered array of carbon nanotubes filled with Fe has been used. The carbon nanotubes are very uniform in diameter and length and are aligned vertically with respect to the SBA-16 film.     

Magnetic field assisting DC electrodeposition: general methods for high-performance Ni nanowire array fabrication

One-dimensional magnetic nanowires are generally thought to show fine axial magnetism for their special high aspect ratio of the shape. However, the magnetic nanowire arrays fabricated by DC electrodeposition in template pores always show a low squareness in parallel to the nanowire direction. We developed two general and simple methods to improve the squareness of the as-fabricated Ni nanowire arrays parallel to the nanowire direction. The nanowires are found to be polycrystalline. The magnetism of the nanowire is also analyzed based on the microstructure.     

Synthesis of bifunctional polymer nanotubes from silicon nanowire templates via atom transfer radical polymerization

As a way to control the surface properties of nanowires and nanotubes, we present a method for growing polymer from the surface of silicon/silica core/shell nanowires. After modification of nanowire surfaces with polymer initiators, Atom Transfer Radical Polymerization (ATRP) was used to grow methacrylate polymer chains from the surface. The resulting structures were characterized by SEM, TEM, and EELS. After etching the silicon cores, the resulting polymer-coated nanotubes will have hydrophilic silica cores with hydrophobic polymer shells.     

Template synthesis and characterization of PbTiO3 nanowire arrays from aqueous solution

Highly ordered PbTiO₃ nanowire arrays were first reported by fabricating within the pores of anodic aluminum oxide (AAO) template in the aqueous solution by liquid-phase deposition method. The structure and morphology of PbTiO₃ nanowire arrays were characterized by SEM and TEM, respectively. The XRD result shows that desired stoichiometric composition could be easily obtained preparing the treatment solution during post-annealing in order to crystallize the nanowires. TEM analyses confirmed that the obtained nanowires composed of large crystals than others made by sol-gel methods. Finally, a possible growth mechanism of the PbTiO₃ nanowires is discussed.     

柔性硅纳米线阵列的制备及光催化性能研究

硅纳米线阵列是利用太阳能解决能源和环境问题的重要材料,然而,可用于柔性器件和生物相容性器件的柔性硅纳米线阵列的制备方法非常有限。本文通过化学气相沉积,以及高分子转移的方法,成功制备了具有不同高分子层厚度的柔性硅纳米线阵列,并研究了高分子层厚度对柔性硅纳米线阵列光催化性能的影响。结果表明,高分子层厚度越小,柔性硅纳米线阵列的光催化性能越强。因此,利用本文提出的制备方法得到的高分子层厚度低至5 μm的柔性硅纳米线阵列,具有作为高效柔性太阳能电池和全光解水系统光电极的潜力。同时,该研究结果也为设计具有高效光能转换能力的柔性纳米线阵列提供了重要依据。     

Conversion of cellulose materials into nanostructured ceramics by biomineralization

Synthesis of hierarchically ordered silica materials having ordered wood cellular structures has been demonstrated through in-situ mineralization of wood by means of surfactant-directed mineralization in solutions of different pH. At low pH, silicic acid penetrates the buried interfaces of the wood cellular structure without clogging the pores to subsequently “molecularly paint” the interfaces thereby forming a positive replica following calcinations. At high pH, the hydrolyzed silica rapidly condenses to fill the open cells and pits within the structure resulting in a negative replica of the structure. Surfactant-templated mineralization in acid solutions leads to the formation of micelles that hexagonally pack at the wood interfaces preserving structural integrity while integrating hexagonally ordered nanoporosity into the structure of the cell walls following thermal treatment in air. The carbothermal reduction of mineralized wood with silica at high temperature produces biomorphic silicon carbide (SiC) materials, which are typical aggregations of β-SiC nanoparticles. To understand the roles of each component (lignin, crystalline cellulose, amorphous cellulose) comprising the natural biotemplates in the transformation to SiC rods, three different cellulose precursors including unbleached and bleached pulp, and cellulose nanocrystals have been utilized. Lignin in unbleached pulp blocked homogeneous penetration of silica into the pores between cellulose fibers resulting in non-uniform SiC fibers containing thick silica layers. Bleached pulp produced uniform SiC rods with camelback structures (80 nm in diameter; ∼50 μm in length), indicating that more silica infiltrates into the amorphous constituent of cellulose to form chunky rather than straight rod structures. The cellulose nanocrystal (CNXL) material produced clean and uniform SiC nanowires (70 nm in diameter; >100 μm in length) without the camelback structure.     

Karman vortex street assisted patterning in the growth of silicon nanowires

A Karman vortex street was employed to pattern catalysts and grow nanomaterial arrays, which were made of a disk-like superstructure built of silicon nanowires; there also existed nanowires connected with the disks.     

Electrochemical characterization of vertical arrays of tin nanowires grown on silicon substrates as anode materials for lithium rechargeable microbatteries

Vertical arrays of one-dimensional tin nanowires on silicon dioxide (SiO₂)/silicon (Si) substrates have been developed as anode materials for lithium rechargeable microbatteries. The process is complementary metal-oxide-semiconductor (CMOS) compatible for fabricating on-chip microbatteries. Nanoporous anodized aluminum oxide (AAO) templates integrated on SiO₂/Si substrates were employed for fabrication of tin nanowires resulting in high surface area of anodes. The microstructure of these nanowire arrays was investigated by scanning electron microscopy and X-ray diffraction. The electrochemical tests showed that the discharge capacity of about 400 mA h g⁻¹ could be maintained after 15 cycles at the high discharge/charge rate of 4200 mA g⁻¹.     

Molten gallium as a catalyst for the large-scale growth of highly aligned silica nanowires

The vapor-liquid-solid (VLS) process is a fundamental mechanism for the growth of nanowires, in which a small size (5-100 nm in diameter), high melting point metal (such as gold and iron) catalyst particle directs the nanowire's growth direction and defines the diameter of the crystalline nanowire. In this article, we show that the large size (5-50 microm in diameter), low melting point gallium droplets can be used as an effective catalyst for the large-scale growth of highly aligned, closely packed silica nanowire bunches. Unlike any previously observed results using gold or iron as catalyst, the gallium-catalyzed VLS growth exhibits many amazing growth phenomena. The silica nanowires tend to grow batch by batch. For each batch, numerous nanowires simultaneously nucleate, grow at nearly the same rate and direction, and simultaneously stop growing. The force between the batches periodically lifts the gallium catalyst upward, forming two different kinds of products on a silicon wafer and alumina substrate. On the silicon wafer, carrot-shaped tubes whose walls are composed of highly aligned silica nanowires with diameters of 15-30 nm and length of 10-40 microm were obtained. On the alumina substrate, cometlike structures composed of highly oriented silica nanowires with diameters of 50-100 nm and length of 10-50 microm were formed. A growth model was proposed. The experimental results expand the VLS mechanism to a broader range.     

非晶SiO2纳米灯笼的制备和表征

在1000 ℃用活性炭把二氧化锡粉末还原成单质锡, 锡作为催化剂, 硅片作为硅源同时作为收集衬底, 在硅片上制备出了非晶SiO2纳米灯笼. 灯笼的一端连在硅片上, 另一端为一个锡球, 中间是一些圆弧状的SiO2纳米线把两端相连. 纳米灯笼具有良好的对称性. 利用扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)、选区电子衍射(SAED) 和HRTEM自带的能谱分析仪(EDS)对样品的表面形貌、微观结构和成分进行了分析研究. 结果表明, 灯笼中SiO2纳米线为非晶态, 结点是晶态锡, 结点表面覆盖一层非晶态的硅的氧化物. 结合实验条件对纳米灯笼的生长机理进行了讨论, 提出了纳米灯笼生长的一个模型.     

Three dimensional architectures of ultra-high density semiconducting nanowires deposited on chip

We report a "clean" and fast process, utilizing supercritical carbon dioxide, for producing ultrahigh densities, up to 10(12) nanowires per square centimeter, of ordered germanium nanowires on silicon and quartz substrates. Uniform mesoporous thin films were employed as templates for the nucleation and growth of unidirectional nanowire arrays orientated almost perpendicular to a substrate surface. Additionally, these nanocomposite materials display room-temperature photoluminescence (PL), the energy of which is dependent on the diameter of the encased nanowires. The ability to synthesis ultrahigh-density arrays of semiconducting nanowires on-chip is a key step in future "bottom-up" fabrication of multilayered device architectures for nanoelectronic and optoelectronic devices.