Shape‐Controlled Growth of Carbon Nanostructures: Yield and Mechanism

Carbon nanostructures with precisely controlled shapes are difficult materials to synthesize. A facet‐selective‐catalytic process was thus proposed to synthesize polymer‐linked carbon nanostructures with different shapes, covering straight carbon nanofiber, carbon nano Y‐junction, carbon nano‐hexapus, and carbon nano‐octopus. A thermal chemical vapor deposition process was applied to grow these multi‐branched carbon nanostructures at temperatures lower than 350 °C. Cu nanoparticles were utilized as the catalyst and acetylene as the reaction gas. The growth of those multi‐branched nanostructures was realized through the selective growth of polymer‐like sheets on certain indexed facets of Cu catalyst. The vapor–facet–solid (VFS) mechanism, a new growth mode, has been proposed to interpret such a growth in the steps of formation, diffusion, and coupling of carbon‐containing oligomers, as well as their final precipitation to form nanostructures on the selective Cu facets.     

Controlled growth of SnO(2) hierarchical nanostructures by a multistep thermal vapor deposition process

Branched and sub-branched SnO(2) hierarchical architectures in which numerous aligned nanowires grew on the surface of nanobelt substrates have been obtained by a multistep thermal vapor deposition route. Branch size and morphology can be controlled by adjusting the temperature and duration of growth. The same approach was used to grow branched ZnO-SnO(2) heterojunction nanostructures. In addition, the third level of SnO(2) nanostructures was obtained by repeating the vapor deposition growth process. This technique provides a general, facile, and convenient approach for preparing even more complex nanoarchitectures, and should open up new opportunities for both fundamental research and applications, such as nanobelt-based three-dimensional nanodevices.     

能源催化材料的电化学合成

电催化是发展可持续洁净能源技术的基础科学,是电化学能源转换和物质转化的关键环节.精准合成催化活性纳米结构是制约很多电催化反应走向实际应用的重要挑战.与湿化学合成、固相合成和气相沉积等传统方法相比,电化学合成是一种简单、快速、廉价及可控的高效催化材料制备方法,也是一种最为直接的一体化电极制备方法.本文综述了近年来利用电化...     

Formation of AlOOH and silica composite hierarchical nanostructures thin film by sol–gel dip-coating for superhydrophobic surface with high adhesion force

Nanosheet AlOOH and silica spheres composite thin film was deposited onto glass by sol–gel dip-coating method through hydrolysis of boiling water immersion. A silica sol and an alumina sol are employed in dipping process for the preparation of hierarchical nanostructures thin film. The morphology and structure of the films were characterized using field emission scanning electron microscopy and X-ray diffraction. The super-hydrophobicity with high adhesion forces can be attributed to both the rough multi-scale structural coating and surface enrichment of low surface energy with the chemical vapor deposition of 1H,1H,2H,2H-perfluorodecyltriethoxysilane.     

Two types of carbon nanocomposites: Graphite encapsulated iron nanoparticles and thin carbon nanotubes supported on thick carbon nanotubes, synthesized using PECVD

In this work, graphite encapsulated Fe nanoparticles and thin carbon nanotubes (CNTs) supported on the pristine CNTs, respectively, were synthesized using plasma enhanced chemical vapor deposition via efficiently controlling the flow rate of discharging CH₄ and H₂ gas. The properties of the obtained hybrid materials were characterized with superconducting quantum interference and field emission measurements. The results showed that the encapsulated Fe nanoparticles had diameters ranging from 1 to 30 nm, and this hybrid nanocomposite exhibited a ferromagnetic behavior at room temperature. Thin CNTs with an average diameter of 6 nm were attached to the surface of the prepared CNTs, which exhibited a lower turn-on field and higher emission current density than the pristine CNTs. The Fe nanoparticles either encapsulated with graphite or used as catalyst for thin CNTs growth were all originated from the pyrolysis of ferrocene.     

Physical and electrical properties of chemical vapor grown GaN Nano/microstructures

Wurtzitic gallium nitride nano- and microleaves were controlled grown through a facile chemical vapor deposition method. This is the first report of GaN nanoleaves, a new morphology of GaN nanostructures. The as-grown GaN structures were characterized by means of X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray, transmission electron microscopy, and selected area electron diffraction. Raman scattering spectra of the GaN leaves were studied. Field effect transistors based on individual GaN nanoleaves were fabricated, and the electrical transport results revealed a pronounced n-type gating effect of the GaN nanostructures.     

Ag作催化剂制备的GaN的形貌及其性能

用化学气相沉积法(CVD)在Si(100)衬底上以Ag纳米颗粒为催化剂制备了微纳米结构的GaN,原料是熔融态的金属Ga和气态的NH3。采用X射线衍射仪(XRD)、透射电镜(TEM)、X-ray能谱仪(EDS)、场发射扫描电子显微镜(SEM)、光致发光能谱(PL)和霍尔效应测试对样品进行了结构、成分、形貌和发光、电学性能分析。结果表明:生成的自组装GaN为六方纤锌矿的类似小梯子的微纳米单晶结构,且在不同的温度下,GaN的发光性能和电学性能也有所不同,相对于强的紫外发光峰,其它杂质发光峰很微弱,且均呈p型导电。对本实验所得到的GaN微纳米结构的可能形成机理进行了探讨。     

Kinetics-driven growth of orthogonally branched single-crystalline magnesium oxide nanostructures

Orthogonally branched single-crystalline magnesium oxide nanostructures were synthesized through a simple chemical vapor transport and condensation process in a flowing Ar/O(2) atmosphere. Other morphologies, such as cubes and nanowires, can also be obtained under different controlled conditions. The formation of different types of nanostructures can be tuned by modifying oxygen partial pressure during the synthesis. All the nanostructures are cubic single-crystalline enclosed by low-index {100} facets. Growth mechanisms for the nanostructures are discussed in detail: different supersaturation ratios, relatively high substrate temperatures, and surface defects in certain crystallographic planes cooperatively take important effects on determining the product morphologies. Structural defect-related blue light emission of the three types of MgO nanostructures was investigated. The MgO nanostructures with abundant morphologies may find applications in various nanodevices, and the kinetics-driven methodology might be exploited to synthesize similar nanostructures of other functional oxide materials.     

Morphological control of synthesis and anomalous magnetic properties of 3-D branched Pt nanoparticles

Morphology-controllable platinum nanostructures could be obtained by modulating the growth kinetics in oleylamine. The nanostructures evolve from spherical particles to branched networks with decreasing reaction temperature, and the complexity of the branched-network nanostructures increases with the extended reaction period. Size-dependent magnetic properties and enhanced ferromagnetism in dodecanethiol-capped Pt branched nanostructures indicate that the permanent magnetic moments are probably introduced by broken symmetry and charge transfer because charge transfers more effectively from dodecanethiol than from oleylamine.     

Growth of nanocrystalline MoO3 on Au(111) studied by in situ scanning tunneling microscopy

The growth of nanocrystalline MoO3 islands on Au(111) using physical vapor deposition of Mo has been studied by scanning tunneling microscopy and low energy electron diffraction. The growth conditions affect the shape and distribution of the MoO3 nanostructures, providing a means of preparing materials with different percentages of edge sites that may have different chemical and physical properties than atoms in the interior of the nanostructures. MoO3 islands were prepared by physical vapor deposition of Mo and subsequent oxidation by NO2 exposure at temperatures between 450 K and 600 K. They exhibit a crystalline structure with a c(4 x 2) periodicity relative to unreconstructed Au(111). While the atomic-scale structure is identical to that of MoO3 islands prepared by chemical vapor deposition, we demonstrate that the distribution of MoO3 islands on the Au(111) surface reflects the distribution of Mo clusters prior to oxidation although the growth of MoO3 involves long-range mass transport via volatile MoO3 precursor species. The island morphology is kinetically controlled at 450 K, whereas an equilibrium shape is approached at higher preparation temperatures or after prolonged annealing at the elevated temperature. Mo deposition at or above 525 K leads to the formation of a Mo-Au surface alloy as indicated by the observation of embedded MoO3 islands after oxidation by NO2. Au vacancy islands, formed when Mo and Au dealloy to produce vacancies, are observed for these growth conditions.     

化学气相沉积法制备氧化锡自组装纳米结构

采用化学气相沉积法在镀有5-10 nm厚金膜的SiO2衬底上, 通过控制生长条件, 实现了二氧化锡纳米结构的自组装生长, 成功制备出了莲花状和菊花状的二氧化锡自组装纳米结构. 利用扫描电子显微镜、X射线衍射等表征分析手段对样品的表面形貌、结构及成份进行表征和研究. 并在此基础上, 讨论了两种自组装纳米结构的生长机制.     

Reversible wettability of a chemical vapor deposition prepared ZnO film between superhydrophobicity and superhydrophilicity

A superhydrophobic ZnO thin film was fabricated by the Au-catalyzed chemical vapor deposition method. The surface of the film exhibits hierarchical structure with nanostructures on sub-microstructures. The water contact angle (CA) was 164.3 degrees, turning into a superhydrophilic one (CA < 5 degrees) after UV illumination, which can be recovered through being placed in the dark or being heated. The film was attached tightly to the substrate, showing good stability and durability. The surface structures were characterized by scanning electron microscopy and atomic force microscopy.     

Synthesis and characterization of unbranched and branched multi-walled carbon nanotubes using Cu as catalyst

Unbranched and branched carbon nanotubes (CNTs) were synthesized by catalytic chemical vapor deposition from methane at 900 °C over a Cu/MgO catalyst. Morphology and structure of the CNTs were characterized by scanning and transmission electron microscopy, and Raman spectroscopy. The effect of methane flow rate on the CNT growth was investigated. The results suggest that the products were transformed from unbranched to branched CNTs with an increase in methane flow rate. The simplicity and controllability of such a preparation technique make it a promising method to synthesize different carbon nanotube structures.     

Enhancement mechanism of field electron emission properties in hybrid carbon nanotubes with tree- and wing-like features

In this work, the tree-like carbon nanotubes (CNTs) with branches of different diameters and the wing-like CNTs with graphitic-sheets of different densities were synthesized by using plasma enhanced chemical vapor deposition. The nanostructures of the as-prepared hybrid carbon materials were characterized by scanning electron microscopy and transmission electron microscopy. The structural dependence of field electron emission (FEE) property was also investigated. It is found that both of the tree- and wing-like CNTs exhibit a lower turn-on field and higher emission current density than the pristine CNTs, which can be ascribed to the effects of branch size, crystal orientation, and graphitic-sheet density.     

Toward the innovative synthesis of columnar CeO2 nanostructures

We report on the preparation of supported columnar CeO(2) nanostructures by a simple catalyst-free chemical vapor deposition process at temperatures as low as 623 K. A suitable choice of experimental parameters enables us to control the structural and morphological features of the resulting ceria nanosystems.     

Synthesis, characterization, and optical properties of In2O3 semiconductor nanowires

In2O3 semiconductor nanowires were synthesized by the chemical vapor deposition method through carbon thermal reduction at 900 degrees C with 95% Ar and 5% O2 gas flow. The In2O3 nanowires were characterized by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence spectroscopy (PL). For the first time, we observed the formation of corundum-type h-In2O3 nanowires and branched In2O3 nanowires. The PL spectra of In2O3 nanowires show strong visible red emission at 1.85 eV (670 nm) at low temperature, possibly caused by a small amount of oxygen vacancies in the nanowire crystal structure.     

SWNTs as catalyst and/or support in the catalytic decomposition of hydrocarbons

Various SWNT samples as either catalyst or catalytic support were used in the chemical vapor deposition (CVD) method for the growth of MWNTs. Catalysts were prepared by the impregnation of SWNT soot with different transition metals. Decomposition of acetylene was investigated at different temperatures (650–720 °C). The quality of both original SWNTs and the newly formed carbon nanostructures was assessed by TEM. A significant difference was found between selectivities of original (known as metallic impurities in SWNT soot) and the posteriorly deposited metallic particles. In the presence of active catalyst SWNT ropes tend to disappear, absorbed into carbon fibers or MWNTs.     

SnO2 nanoparticle-functionalized boron nitride nanotubes

Boron nitride nanotubes (BNNTs) were synthesized by a carbon-free chemical vapor deposition method using boron and metal oxide as reactants. Then SnO(2) nanoparticles were functionalized on them via a simple wet chemistry method. Detailed transmission electron microscopy (TEM) observations reveal that SnO(2) nanoparticles may cover the tube surface or be encapsulated in tube channels. The lattice distances of both BNNT and SnO(2) have been changed due to the strong interactions between them. The band gap energy of SnO(2) particles is found enlarged due to the size effect and interaction with BNNTs.     

Atmospheric pressure chemical vapor deposition: an alternative route to large-scale MoS2 and WS2 inorganic fullerene-like nanostructures and nanoflowers

Large-scale MoS2 and WS2 inorganic fullerene-like (IF) nanostructures (onionlike nanoparticles, nanotubes) and elegant three-dimensional nanoflowers (NF) have been selectively prepared through an atmospheric pressure chemical vapor deposition (APCVD) process with the reaction of chlorides and sulfur. The morphologies were controlled by adjusting the deposition position, the deposition temperature, and the flux of the carrier gas. All of the nanostructures have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). A reaction mechanism is proposed based on the experimental results. The surface area of MoS2 IF nanoparticles and the field-emission effect of as-prepared WS2 nanoflowers is reported.     

Macroscopically Oriented Magnetic Core-regularized Nanomaterials for Glucose Biosensors Assisted by Self-sacrificial Label

Magnetic core-regular nanostructures composed of magnetite and regular Prussian blue was prepared by self-sacrificial macro-oriented method. Magnetic graphene oxide (MGO) was vertically oriented on the surface of home-made screen-printing electrode with the help of constant magnetic field (CMF).Then regular nanostructured Prussian blue (RPB) was realized by chemical reaction through an aerosol deposition. Finally, glucose oxidase (GOx) was immobilized by glutaraldehyde cross-linking to fabricate glucose biosensors. The linear range of CMF-RPB/MGO sensor towards glucose was 0.03∼1.35 mM, and the detection limit was 13.4 μM. The CMF-RPB/MGO sensor could apply to analyze glucose in human serum samples.