Simple Chemical Vapor Deposition Research Articles

Thermal and chemical durability of nitrogen-doped carbon nanotubes

Nitrogen-doped carbon nanotubes (CNx tubes) with nitrogen content of 7.6 at.% are synthesized on carbon papers. Thermal and chemical stability of the nanotubes are investigated by thermogravimetric anal- ysis, differential scanning calorimetry and X-ray pho- toelectron spectroscopy techniques. The results indicate that the nitrogen can be firmly kept in the nanotubes after annealing at 300 C in air. Under an argon atmosphere, the nitrogen would not release until 670 C, and half of the nitrogen incorporated is released after annealing at 700 C for 30 min. Chemical stability investigation indicates that the nitrogen incorporated in the nanotubes is very stable under the thermal and acid environment comparable to working condition of proton exchange membrane (PEM) fuel cells. Profile of the nitrogen species inside the nanotubes reveals that graphite-like nitrogen releases slower than any other kind of nitrogen in the nanotubes during the chemical stability measure- ment. These CNx tubes synthesized by this simple chemical vapor deposition method are expected to be

Phase-controlled synthesis of nickel silicide nanostructures

Dense single-crystalline Ni2Si nanowires, Ni3Si2 nanowires and nanorods, and NiSi nanowires have been successfully synthesized in large-scale on the surface of Ni foam via a simple chemical vapor deposition of SiH4 at 450–600°C. It is indicated that the reaction temperature and the flow rate of SiH4 play an important role in the control of phases and morphologies of nickel silicide nanostructures. The temperature controls the balance of Ni-diffusion and the degree of supersaturation of Si in Ni, thus producing different nickel silicide phases, whereas the different flow rates of SiH4 lead to the different nickel silicide morphologies by controlling the size and the quality of the nucleation centers. We expect that our synthesis approach and results will provide valuable information for the fabrication and application of other metal silicide nanostructures.

Cu-Doped ZnO Hemispherical Shell Structures: Synthesis and Room-Temperature Ferromagnetism Properties

We report a simple chemical vapor deposition method to fabricate Cu-doped ZnO hemispherical shell structures with room-temperature ferromagnetism (RTFM). Through a series of controlled experiments by changing the growth temperature and reaction time, we observe the evolution of product morphology from whole spherical structures into partially broken shells and hemispherical shells at different temperatures together with the reinforced hemispherical shells with the reaction time extended. The growth mechanism of the ZnO:Cu hemispherical shell structures has been proposed to involve the synthesis of Cu-doped Zn sphere, surface oxidation, and sublimation of the inner Zn from the broken shell. The structural and optical properties of the ZnO:Cu system with different Cu contents (below 4%) were investigated by X-ray diffraction, Raman spectroscopy, and photoluminescence measurements indicating that the Cu ions were successfully substituted into the Zn2+ lattice sites, and more intrinsic structural defects were...

Effect of catalyst nanoparticle size on growth direction and morphology of InN nanowires

Au-assisted growth of InN nanowires (NWs) was accomplished by a simple chemical vapor deposition system. The as-prepared InN NWs exhibit two morphologies with different growth directions: periodic NWs (PNWs) and smooth NWs (SNWs) along <0001> and $ <\!\! 11\bar 20\! >$<112¯0>, respectively. The PNWs with crinoids morphology resulted when larger Au particles (∼40 nm in diameter) were used, while the SNWs with smooth sidewalls were obtained when smaller Au particles (∼10 nm in diameter) served as the collector. Furthermore, the mechanism of this growth behavior was discussed in terms of the effect of catalyst nanoparticle size.

Van der Waals Epitaxy of MoS2 Layers Using Graphene As Growth Templates

We present a method for synthesizing MoS(2)/Graphene hybrid heterostructures with a growth template of graphene-covered Cu foil. Compared to other recent reports, (1, 2) a much lower growth temperature of 400 °C is required for this procedure. The chemical vapor deposition of MoS(2) on the graphene surface gives rise to single crystalline hexagonal flakes with a typical lateral size ranging from several hundred nanometers to several micrometers. The precursor (ammonium thiomolybdate) together with solvent was transported to graphene surface by a carrier gas at room temperature, which was then followed by post annealing. At an elevated temperature, the precursor self-assembles to form MoS(2) flakes epitaxially on the graphene surface via thermal decomposition. With higher amount of precursor delivered onto the graphene surface, a continuous MoS(2) film on graphene can be obtained. This simple chemical vapor deposition method provides a unique approach for the synthesis of graphene heterostructures and surface functionalization of graphene. The synthesized two-dimensional MoS(2)/Graphene hybrids possess great potential toward the development of new optical and electronic devices as well as a wide variety of newly synthesizable compounds for catalysts.

Patterned Growth of In<SUB>2</SUB>O<SUB>3</SUB> Spheres Organized by Radially-Aligned In<SUB>2</SUB>O<SUB>3</SUB> Nanobelts

Sphere-like patterns arranged by radially-aligned In2O3 nanobelts were obtained via a simple chemical vapor deposition method. As-synthesized products were investigated by field-emission scanning electronic microscopy, transmission electronic microscopy and EDX spectra. The well-organized orientations of these nanobelts were ascribed to the interaction between dynamic micro-electromagnetic fields formed on indium droplet surface and the lattice vibrations in nanometer-sized In2O3 crystals. Further analysis showed that a small quantity of W impurities made a great difference in the formation of organized patterns.

Functional microspheres of graphene quantum dots

Graphene-quantum-dot microspheres (GQDSs) have been prepared by assembly of graphene quantum dots (GQDs) via a water-in-oil (W/O) emulsion technique without the addition of any surfactants. Although made of quantum-sized graphene dots, the as-formed GQDSs are solid and remain intact after slight ultrasonication. The versatile W/O emulsion method allows the in situ intercalation of functional nanocomponents into the GQDSs for specific applications. As exemplified by the Fe3O4-containing GQDSs, Fe3O4–GQDSs exhibit a large magnetic response. Furthermore, the embedded Fe3O4 nanoparticles in GQDSs can act as the catalysts for the growth of carbon nanotubes (CNTs), which opens the opportunities for fabricating new complex structures of CNTs surrounding GQDSs by simple chemical vapor deposition.

Nanographitic layer-mediated synthesis of carbon-TiO2 hybrid nanobelts by metalorganic chemical vapor deposition

Vertically-aligned, self-assembled carbon–Fe:TiO2 hybrid nanobelts were synthesized using a simple and low-cost metalorganic chemical vapor deposition (MOCVD). Residual C, a by-product of MOCVD reaction, was utilized to form a nanographitic layer at the tip of the nanobelts, by which the Fe:TiO2 nanobelt growth was mediated as the growth temperature was determined judiciously at 510°C. The Fe:TiO2 coating on the nanographitic layer is governed by Volmer–Weber and step-flow growth modes. The resultant vertically-aligned C–Fe:TiO2 hybrid nanobelts have significant potential for various photocatalysis, solar cell, and Li-ion battery applications.

Quenching of photocatalytic activity and enhancement of photostability of ZnO particles by polydimethysiloxane coating

ZnO particles with a size range of 50–150 nm were coated with polydimethylsiloxane (PDMS) with a thin film thickness of 3–4 nm using a simple ambient-pressure chemical vapor deposition method. Surfaces consisting of the PDMS-coated ZnO nanoparticles were found to be superhydrophobic with a water contact angle >160°. The superhydrophobicity was sustained in the presence of UV light. Photocatalytic activity and photocorrosion of ZnO were nearly completely quenched in the presence of PDMS-coating. It is suggested that our PDMS-coating can be of potential interest for the application of ZnO in UV protection agents and energy and electronic devices.

Vertically aligned ZnO–ZnGa2O4 core–shell nanowires: from synthesis to optical properties

Dense and vertically aligned ZnO–ZnGa2O4 core–shell nanowires were synthesized in large scale on a-plane sapphire substrates by a simple two-step chemical vapor deposition method. The synthesized ZnO–ZnGa2O4 core–shell nanowires were connected through their base by a thick underlayer of the same material realizing electrical contact of the nanostructured array. X-ray diffraction and transmission electron microscopy analyses of the core–shell nanowires reveal that the ZnO cores and ZnGa2O4 shells of the core–shell nanowires are of single-crystal quality and have aligned crystallographic orientations. The ultraviolet–visible diffuse reflectance spectra of the core–shell nanowires showed two sharp edges corresponding to near-band-edge absorption contributed by the ZnO cores and the ZnGa2O4 shells. Moreover, the room-temperature photoluminescence spectra of the core–shell nanowires gave three UV emission peaks coming from the ZnGa2O4 shells and the ZnO cores. The dense and vertically aligned ZnO–ZnGa2O4 core–shell nanowires showing promising photoelectric properties offer an ideal structure for light harvesting applications such as a photoanode in a photoelectrochemical water splitting cell.

Large-scale: Synthesis, microstructure, and FT-IR property of SiC nanowires

Large-scale SiC nanowires have been synthesized via reacting silicon powder with carbon powder using Ni2O3 as catalyst by simple chemical vapor deposition method. The mixed powders were heated in an alumina horizontal tube furnace up to 1350 °C for 1 h in an argon atmosphere. Characterization by scanning electron microscope, transmission electron microscope, and X-ray diffractometer indicated that the nanowires covered with a thin layer of amorphous SiOx. The 3C–SiC nanowires were formed by vapor–liquid–solid growth mechanism and they have diameters of about 20–90 nm. The result of FT-IR spectrum shows the nanowires were composed of SiC and amorphous of silicon oxide.

Fabrication of cone-shaped CNF/SiC-coated Si-nanocone composite structures and their excellent field emission performance

Novel cone-shaped carbon nanofiber (CNF)/silicon carbide (SiC)-coated Si-nanocone (Si-NC) composite structures with excellent field emission (FE) performance have been fabricated by a simple microwave plasma chemical vapour deposition process. Transmission electron microscopy analyses reveal that the newly developed cone-shaped composite structures are composed of bamboo-like herringbone CNFs grown vertically on the tips of conical SiC layers with a flat-top Si cone embedded underneath. For this CNF/SiC-coated Si-NC composite array, a ultra-low threshold field of 0.32 V μm(-1) (at 10 mA cm(-2)), a large emission current density of 668 mA cm(-2) at 1.05 V μm(-1), and a field enhancement factor as high as ~48,349 are obtained. In addition, the FE lifetime test performed at a large emission current density of 200 mA cm(-2) under an applied field of 1 V μm(-1) shows no discernible decay during a period of over 260 minutes. We deduce that this superior FE performance can be attributed to the specific bamboo-like herringbone CNFs with numerous open graphitic edges and a faceted top end, and the conical base SiC/Si structures with sufficient adhesion to the substrate surface. Such a novel structure with promising emission characteristics makes it a potential material for electron field emitters.

One-step fabrication of β-Ga2O3–amorphous-SnO2 core–shell microribbons and their thermally switchable humidity sensing properties

We reported the fabrication of a highly sensitive, fast, and thermally switchable humidity sensor based on a β-Ga2O3–amorphous-SnO2 core–shell microribbon, which was synthesized via a simple one-step chemical vapour deposition. The as-grown microribbons were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) and the results indicated that the microribbon has a well-defined core–shell structure with β-Ga2O3 in the core and amorphous SnO2 in the shell. At 25 °C, the conductivity of the humidity sensor at 75% relative humidity (RH) was three orders of magnitude larger than that in dry air (5% RH). The response time and recovery time were ∼28 and ∼7 s, respectively, when RH was switched between 5 and 75%. Interestingly, by changing the temperature between 12 and 40 °C at 75% RH, the sensitivity can be tuned between ∼105 (12 °C) and ∼102 (40 °C). Typical thermally switchable properties of β-Ga2O3–amorphous-SnO2 core–shell microribbons at 75% RH were demonstrated using a heating–cooling cycle between 20 and 30 °C. The possible mechanisms have been proposed based on the novel core–shell structures and water adsorption–desorption processes. Our findings pave the way for new types of humidity sensors and thermal switches.

ZnO–ZnGa2O4core–shell nanowire array for stable photoelectrochemical water splitting

A dense array of vertically aligned ZnO-ZnGa(2)O(4) core-shell nanowires was synthesized on a large scale on an a-plane sapphire substrate by a simple two-step chemical vapor deposition method. The ZnO cores and ZnGa(2)O(4) shells of the nanowires are of single crystal quality and have aligned crystallographic orientations as evidenced from XRD and TEM analyses. Mott-Schottky analysis and voltage onset from the photocurrent-voltage curve confirm an n-type semiconductor property, a flat-band potential of -0.4 V (versus NHE) and a carrier density of 7 × 10(18) cm(-3) for the ZnO-ZnGa(2)O(4) core-shell nanowires. A stable and large photocurrent of 1.2 mA cm(-2) was obtained with the ZnO-ZnGa(2)O(4) core-shell nanowire array when used as a photoanode at an applied bias of +0.7 V (versus Ag/AgCl) under a 300 W xenon lamp illumination. Moreover, a low dark current of <10(-4) mA cm(-2) was obtained at an applied bias of +0.7 V (versus Ag/AgCl) without light illumination for the ZnO-ZnGa(2)O(4) nanowire array. These results suggest that the dense array of ZnO-ZnGa(2)O(4) core-shell nanowires provides enhanced electronic properties and stable anti-photocorrosion ability and, therefore, is promising as a photoanode in photoelectrochemical water splitting.

Electroluminescence from ZnO nanowires homojunction LED grown on Si substrate by simple chemical vapor deposition

ZnO nanowires homojunction LED with phosphorus-doped p-ZnO nanowires/n-ZnO nanowires structure was fabricated on Si substrate by simple chemical vapor deposition. The scanning electron microscope show well-aligned undoped ZnO nanowires and phosphorus doped ZnO nanowires with uniform diameter, length, and density were grown perpendicularly on Si substrate. The phosphorus related acceptor emissions were observed from photoluminescence spectra of phosphorus-doped ZnO nanowires at 20K. Moreover, the current–voltage measurement of ZnO nanowires homojunction LED showed a good rectifying behavior with a turn-on voltage was about 3.8V and a reverse breakdown voltage was about 6V. Distinct electroluminescence with ultraviolet and visible emissions was detected from this device at room temperature.

Highly Stable and Magnetically Recyclable Mesoporous Silica Spheres Embedded with FeCo/Graphitic Shell Nanocrystals for Supported Catalysts

We have synthesized highly stable and magnetically recyclable mesoporous silica spheres embedded with FeCo-graphitic carbon shell nanocrystals (FeCo/GC@MSS) by a simple one-step chemical vapor deposition (CVD) method. Solid core-mesoporous shell silica spheres with an average diameter of ∼400 nm are used as supports not only for the synthesis of the FeCo/GC nanocrystals but also for catalysts after the synthesis of the FeCo/GC@MSS. The FeCo/GC nanocrystals in the mesoporous silica spheres exhibit superparamagnetism with ultrahigh saturation magnetization up to 215 e.m.u./metal g at room temperature. The FeCo/GC@MSS is chemically stable against acid etching and oxidation, which enable the FeCo/GC@MSS to be used as a support for an acid catalyst, phosphomolybdic acid (PMA). We have shown that PMA-loaded FeCo/GC@MSS works as an excellent recyclable reagent system that catalyzes propargylation of 1,3-diphenyl-2-propyn-1-ol with phenol.

Synthesis and photoluminescence of AlN:Mn hexagonal maze-like complex nanostructure

The AlN:Mn hexagonal maze-like complex nanostructure was prepared via a simple thermal chemical vapor deposition process without structure-directing templates or catalysts. The optical property of the product was investigated by room-temperature photoluminescence (PL) measurement. Two emission bands centered at 490nm and 600nm, respectively. In addition to a familiar red-orange band centered at 600nm originating from intra 3d-electrons transition of Mn2+ ion, another strong broad blue-green band around 490nm is related to VAl3−−3×ON+ defect complexes. The results indicate that the AlN:Mn maze-like complex nanostructure has a certain amount of Al vacancies, and the growth mechanism can be ascribed to nucleus arrangement and preferential growth.

Single-crystal SnO2 nanoshuttles: shape-controlled synthesis, perfect flexibility and high-performance fieldemission

Vertically aligned single-crystalSnO2 nanoshuttle arrays with uniform morphology and a relatively high aspect ratio weresynthesized by a simple hot-wall chemical vapor deposition (CVD) method. It was foundthat regulating the growth temperature gradient could change the shape of theSnO2 nanostructure from nanoshuttles to nanochisels and nanoneedles, and aself-catalyzing growth process was responsible for tunable morphologies ofSnO2 nanostructures. Theas-synthesized SnO2 nanoshuttles showed ultrahigh flexibility and strong toughness with a large elastic strain of ∼ 6.2, which is much higher than reported for Si and ZnO nanowire as wellas most crystalline metallic materials. The field emitter fabricated usingSnO2 nanoshuttle arrays has a low turn-on electric field of around0.6 V µm − 1, and a high field emission current density of above10 mA cm − 2, which is comparable with the highest emission current density of carbon nanotube andnanowire field emitters.

Enhanced Field Emission Performance of Ga-Doped In2O3(ZnO)3 Superlattice Nanobelts

Ga-doped In2O3(ZnO)3 nanobelts were successfully fabricated via a simple chemical vapor deposition (CVD) process. The morphology, microstructure, and composition of the nanobelts were characterized by scanning electron microscopy, high resolution transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectroscopy. The results confirm the formation of In2O3(ZnO)3 superlattice nanobelts doped with Ga. The field-emission studies show a low turn-on electrical field, high field enhancement factor, and a good stability of the emission current. These results are valuable for the design, fabrication, and optimization of field emitters.

Characterization of phenylene-bridged hybrid mesoporous materials incorporating arenetricarbonyl complexes (–C 6H 4Me(CO) 3–; Me = Cr, Mo) and their catalytic activities

The successful construction of arenetricarbonyl complexes (–C 6H 4Me(CO) 3–; Me = Cr, Mo) was achieved through the direct modification of phenylene (–C 6H 4–) moieties of phenylene-bridged hybrid mesoporous materials (HMM-ph) by the simple chemical vapor deposition (CVD) of corresponding metal hexacarbonyls. The pore structure as well as high surface area of HMM-ph were retained even after CVD treatment. It was found that HMM-ph incorporating an arenetricarbonyl molybdenum complex (HMM-phMo(CO) 3) exhibited higher catalytic performance for the polymerization of phenylacetylene and dehydrochlorination of 2-chloro-2-methylbutane than HMM-phCr(CO) 3. Various spectroscopic investigations revealed that the strength of the chemical bond between the phenylene ligand and metal center of the arenetricarbonyl complexes affects the catalytic performance of HMM-phMe(CO) 3 (Me = Cr, Mo).