Synthesis of indium-catalyzed Si nanowires by hot-wire chemical vapor deposition

Indium (In) catalyzed silicon nanowires (SiNWs) were synthesized by using hot-wire chemical vapor deposition (HWCVD) technique. Indium droplets were deposited on Si substrates by hot-wire evaporation of In wire, which was immediately followed by the growth of SiNWs from the droplets. Three sets of samples were prepared by varying the length of In wires, l, as 3, 1 and 0.5 mm. The sizes of In catalyst droplets decreased from 271.4 ± 66.8 to 67.4 ± 16.6 nm when the l was reduced from 3 to 0.5 mm. Larger size of In droplets (271.4 ± 66.8 nm) was found to induce the growth of worm-like NWs. The decrease in size of In catalyst droplets induced the formation of aligned and tapered NWs with smaller tips. The smallest value of tapering parameter, T_p of 40.5 nm/μm is correlated to the SiNWs induced by the smallest size of In droplets (67.4 ± 16.6 nm). The as-grown SiNWs showed high purity and good crystalline structure.     

Few-layer graphene direct deposition on Ni and Cu foil by cold-wall chemical vapor deposition

We report an alternative synthesis process, cold-wall thermal chemical vapor deposition (CVD), is replied to directly deposit single-layer and few-layer graphene films on Ar plasma treated Ni and Cu foils using CH4 as carbon source. Through optimizing the process parameters, large scale single-layer graphene grown on Ni foil is comparable to that grown on Cu foil. The graphene films were able to be transferred to other substrates such as SiO2/Si, flexible transparent PET and verified by optical microscopy, Raman microscopy and scanning electron microscopy. The sheet resistance and transmission of the transferred graphene films on PET substrate were also discussed.     

Synthesis and characterization of indium nitride nanowires by plasma-assisted chemical vapor deposition

High-quality indium nitride (InN) nanowires were synthesized in a high temperature furnace on Au-coated Si substrates through the reaction of indium metal vapor with highly reactive nitrogen radicals generated by N₂ plasma. Highly-reactive nitrogen radicals provided a wide process window for the synthesis of InN nanowires by lowering the process temperature to avoid the decomposition of InN. X-ray diffraction, transmission electron microscopy and Raman spectra further showed that the as-synthesized InN nanowires were perfect single crystallites of wurtzite structure with the growth direction along [110].     

Synthesis of silicon carbide nanowires by solid phase source chemical vapor deposition

In this paper, we report a simple approach to synthesize silicon carbide (SiC) nanowires by solid phase source chemical vapor deposition (CVD) at relatively low temperatures. 3C-SiC nanowires covered by an amorphous shell were obtained on a thin film which was first deposited on silicon substrates, and the nanowires are 20–80 nm in diameter and several μm in length, with a growth direction of [200]. The growth of the nanowires agrees well on vapor-liquid-solid (VLS) process and the film deposited on the substrates plays an important role in the formation of nanowires.     

热化学气相沉积法在硅纳米丝上合成碳纳米管

利用热化学气相沉积法在负载不同厚度催化剂的硅纳米丝(SiNW)表面生长碳纳米管(CNTs),探讨了生长条件对所合成SiNW-CNT的结构和场发射特性的影响.这种类似树状的三维结构具有较高碳纳米管表面密度及降低的电场筛除效应等潜在优势.使用拉曼光谱( Raman)、电子显微镜(SEM)、透射电子显微镜(TEM)、能量扩散分光仪(EDS)分析了碳纳米管的结构性质,并在高真空下施加电场测得碳纳米管的场发射特性.结果表明:随硅纳米丝上负载催化剂镍膜厚度的变化,所合成碳纳米管的表面特性、结晶结构及功函数改变,导致电子发射难易程度的改变,进一步影响碳纳米管的场发射特性.     

Synthesis and optical properties of ZnTe single-crystalline nanowires

Single-crystalline ZnTe nanowires with the zincblende structure have been synthesized on silicon (Si) substrates via a vapor phase transport method. The ZnTe (99.99%) powders were used as the source, and 10 nm-thick thermal evaporated gold (Au) film was used as the catalyst. The as-prepared ZnTe nanowires have diameters of 30-80 nm and lengths of more than 10 microm. The products were analyzed by X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. Optical properties of these nanowires were investigated by room-temperature Raman scattering spectrum and temperature-dependent photoluminescence measurements. The results show that the as-prepared ZnTe nanowires are of high crystal quality.     

Synthesis of dense, single-crystalline CrO2 nanowire arrays using AAO template-assisted chemical vapor deposition

High-density, vertically aligned CrO(2) nanowire arrays were obtained via atmospheric-pressure CVD assisted by AAO templates. The CrO(2) nanowire arrays show remarkably enhanced coercivity compared with CrO(2) films or bulk. It was found that the length of the nanowires is greatly influenced by the pore diameter of the AAO template used. The growth mechanism and the pore size dependence of the CrO(2) nanowire arrays are discussed. The present method provides a useful approach for the synthesis of CrO(2) nanowire arrays. Such highly ordered nanowire arrays within an AAO template may have important applications in ultrahigh-density perpendicular magnetic recording devices and the mass production of spintronic nanodevices.     

Growth of InAs quantum dots on GaAs nanowires by metal organic chemical vapor deposition

InAs quantum dots (QDs) are grown epitaxially on Au-catalyst-grown GaAs nanowires (NWs) by metal organic chemical vapor deposition (MOCVD). These QDs are about 10-30 nm in diameter and several nanometers high, formed on the {112} side facets of the GaAs NWs. The QDs are very dense at the base of the NW and gradually sparser toward the top until disappearing at a distance of about 2 μm from the base. It can be concluded that these QDs are formed by adatom diffusion from the substrate as well as the sidewalls of the NWs. The critical diameter of the GaAs NW that is enough to form InAs QDs is between 120 and 160 nm according to incomplete statistics. We also find that these QDs exhibit zinc blende (ZB) structure that is consistent with that of the GaAs NW and their edges are faceted along particular surfaces. This hybrid structure may pave the way for the development of future nanowire-based optoelectronic devices.     

Growth of single-crystalline AlZnO nanorods by simple vapor deposition method

Well-aligned AlZnO nanorod arrays with various Al concentrations and various diameters were prepared on silicon substrate by a simple vapor deposition with separate sources at different temperatures. Field emission scanning electron microscope (FESEM) and transmission electron microscopy (TEM) were carried out to characterize morphology and microstructure. X-ray fluorescence shows that the atomic ratio of Al/(Al + Zn) of the arrays is determined to be about 3% and 1.6%, respectively. The Burstein-Moss (BM) shift of the strong ultraviolet emission is observed due to Al incorporation.     

Synthesis and photoluminescence of zinc sulfide nanowires by simple thermal chemical vapor deposition

We present a synthetic method of zinc sulfide nanowires by a simple and safe reaction of zinc oxide and iron sulfide powders on a gold-coated silicon substrate through chemical vapor transport and condensation. High quality ZnS nanowires with single crystalline wurtzite structures are grown along [0 0 1] direction with diameters in the range of 10–30 nm and lengths up to tens of micrometers. Photoluminescence spectrum shows strong emission near 339 nm. These nanowires with cleaved ends could be a prominent candidate material for a nanoscale cavity as a ultra-violet nanolaser.     

Synthesis of isotopically-labeled graphite films by cold-wall chemical vapor deposition and electronic properties of graphene obtained from such films

We report the synthesis of isotopically-labeled graphite films on nickel substrates by using cold-wall chemical vapor deposition (CVD). During the synthesis, carbon from ¹²C- and ¹³C-methane was deposited on, and dissolved in, a nickel foil at high temperature, and a uniform graphite film was segregated from the nickel surface by cooling the sample to room temperature. Scanning and transmission electron microscopy, micro-Raman spectroscopy, and X-ray diffraction prove the presence of a graphite film. Monolayer graphene films obtained from such isotopically-labeled graphite films by mechanical methods have electron mobility values greater than 5000 cm²·V⁻¹·s⁻¹ at low temperatures. Furthermore, such films exhibit the half-integer quantum Hall effect over a wide temperature range from 2 K to 200 K, implying that the graphite grown by this cold-wall CVD approach has a quality as high as highly oriented pyrolytic graphite (HOPG). The results from transport measurements indicate that ¹³C-labeling does not significantly affect the electrical transport properties of graphene.     

静态化学气相沉积法制备SiC纤维的拉伸强度分布研究

以沥青基炭单丝为基体,一甲基三氯硅烷为前驱体,使用静态化学气相沉积工艺,在1473K,常压环境下制备了SiC纤维.使用电子万能试验机测试了同一批次纤维的拉伸强度,结果表明其为双峰直方图分布.使用光学显微镜和扫描电子显微镜对纤维的形貌结构进行了表征.沿着反应器方向,不同区域的纤维依次表现为颗粒状、球状、平滑和倒圆锥结构.这些结构的差别导致了纤维力学强度的双峰分布.对沉积机制的分析表明,物料损耗效应和反应器两端的流场稳定性是影响纤维结构的主要因素.     

Thermoelectric properties of individual single-crystalline PbTe nanowires grown by a vapor transport method

We report the thermoelectric performance of individual PbTe nanowires with sizes ranging from 76 to 436 nm grown from a vapor transport method that synthesizes high-quality, single-crystalline PbTe nanowires. Independent measurements of temperature-dependent Seebeck coefficient (S), thermal conductivity (κ) and electrical conductivity (σ) of individual PbTe nanowires were investigated. By varying the nanowire size, the simultaneous increase and decrease of S (-130 μV K(-1)) and κ (1.2 W m(-1) K(-1)), respectively, are achieved at room temperature. Our results demonstrate the enhanced thermoelectric properties of individual single-crystalline PbTe nanowires, compared to that of bulk PbTe, and can provide guidelines for future work on nanostructured thermoelectrics based on PbTe.     

爆炸辅助气相沉积法制备炭纳米线的研究

根据爆炸辅助气相沉积法生长碳纳米管的机理,设计了两种制备炭纳米线的方案:(1)使用低活性铁-镍二元金属催化剂;(2)对钴催化剂作用下碳纳米管的生长实施冷冻。透射电子显微镜显示这两种方法制备的炭纳米线均为纳米颗粒组装而成,具有非常粗糙的表面。其中,使用铁-镍二元催化剂所制炭纳米线直径分布不均匀,黏结情况严重;而在冷冻钴催化剂作用下炭纳米管生长过程所得的炭纳米线直径分布比较均匀,黏结情况也大为减少。这两种纳米线的差别与金属催化剂的活性有关。光催化降解亚甲基蓝实验表明:冷冻碳纳米管生长所得炭纳米线具有良好的催化辅助功能,可以提高ZnS纳米晶的光催化活性。     

Synthesis and alignment of Zn and ZnO nanoparticles by laser-assisted chemical vapor deposition

A simple, versatile, and fast laser-assisted chemical vapor deposition (LCVD) technique that produces linear arrays of Zn and ZnO nanoparticles on a silicon substrate, covering an extended region, is described. A series of consecutive steps is involved in the synthesis and alignment of Zn/ZnO nanoparticles. First, a Lloyd's mirror arrangement is employed to produce two types of periodic nanostructure, i.e., nanoripples and nanoprotrusions. Next, the nanostructured substrate is laser irradiated at a fluence of 60?mJ?cm(-2) in the presence of the metall-organic (MO) precursor gas diethylzinc (DEZn). The evolution of the Zn nanocrystals by LCVD processing was studied as a function of precursor gas pressure and laser fluence by ex situ high-resolution scanning electron microscopy (SEM). Laser irradiation fulfills a double role: it decomposes the adsorbed precursor and causes the evolution of resulting Zn into aligned aggregates of zinc nanoparticles. The Zn nanoparticles react with oxygen upon high-temperature thermal annealing to yield aligned assemblies of ZnO nanoparticles. The production of ZnO was confirmed by x-ray diffraction (XRD) and photoluminescence spectra. This technique is general and could be used in a large number of substrate/precursor combinations.     

Fast growth of large single-crystalline WS2 monolayers via chemical vapor deposition

Nano Research - Two-dimensional (2D) tungsten disulfide (WS2) has emerged as a promising ultrathin semiconductor for building high-performance nanoelectronic devices. The controllable synthesis of...     

Synthesis of vertically oriented GaN nanowires on a LiAlO2 substrate via chemical vapor deposition

Vertically oriented nanowires (NWs) of single-crystalline wurtzite GaN have been fabricated on γ-LiAlO₂ (100) substrate coated with a Au layer, via a chemical vapor deposition process at 1000 °C using gallium and ammonia as source materials. The GaN NWs grow along the nonpolar [100] direction with steeply tapering tips, and have triangular cross-sections with widths of 50–100 nm and lengths of up to several microns. The GaN NWs are formed by a vapor-liquid-solid growth mechanism and the tapering tips are attributed to the temperature decrease in the final stage of the synthesis process. The aligned GaN NWs show blue-yellow emission originating from defect levels, residual impurities or surface states of the GaN NWs, and have potential applications in nanotechnology.     

ZnO nanocrystals synthesized by physical vapor deposition

Various types of zinc oxide (ZnO) nanocrystais were synthesized by physical vaporization of zinc powders without the presence of catalysts and a subsequent exposure to air at a high temperature. These crystals were found to be composed of ZnO nanowires, sheets, and tetrapods. They were observed to crystallize as wurtzite ZnO single crystals. The nanowires are about 120 nm in diameter on average and up to a few dozens of micrometers in length, making aspect ratios higher than 10. The growth direction of the nanowires was identified to be the [001] direction of wurtzite ZnO structure. It was found from microscopic analyses that these ZnO nanowires can be highly flexible. The values for the thickness of ZnO sheets are scattered, averaging 100 nm. The tetrapods may have a different number of projections radiating from one central node.     

Controlled DNA-templated metal deposition: towards ultra-thin nanowires

In this paper, we report the metallization of a dsDNA template using a novel photography-derived two-step strategy in which dsDNA is first complexed with Ag(I) ions and then irradiated with UV light at 254 nm. The nucleobases act as light harvesters and sensitizers, triggering the photoreduction of the complexed silver ions. This process yields a silver nanoparticles blueprint along the DNA strand. The silver latent image is then developed by depositing metallic nickel through an electroless plating process. This photography-derived procedure generates very homogeneous and evenly distributed strings of silver-core/nickel-shell nanoparticles. Although still discontinuous, we believe that such chains can serve as the base for obtaining continuous metal nanowires. Furthermore, this process can most likely be extended to other plating metals, resulting in a broadly general procedure for metallizing DNA with a variety of different materials. Because of the intrinsic simplicity in using light as the key step, this methodology might be amenable to large-scale development, eventually leading to a very efficient molecular-photolithography process.