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.     

Seedless growth of free-standing copper nanowires by chemical vapor deposition

Free-standing copper nanowires were synthesized by a chemical vapor deposition process at low substrate temperatures using Cu(etac)[P(OEt)3]2 as a precursor. The process requires neither templates nor catalysts to produce copper nanowires of 70-100 nm in diameter, which exhibited high purity and crystallinity with [111] orientation. The grain structures of the films deposited from a series of Cu(I) alkyl 3-oxobutanoate complexes indicated that the high precursor stability was responsible for the columnar growth of the grains, which was evolved to the nanowires eventually.     

Growth and luminescence of ternary semiconductor ZnCdSe nanowires by metalorganic chemical vapor deposition

ZnCdSe alloy nanowires were successfully grown on the GaAs (100) substrate by metalorganic chemical vapor deposition using Au as a catalyst. The nanowires display two distinct types of morphology. The majority of them are straight, uniform in diameter, and have a smooth surface. However, a significant portion of them contain one or two constrictions along their length. The alloy is found to be rich in Zn; its composition, as determined from X-ray diffraction and energy-dispersive X-ray microanalysis, is close to Zn(0.9)Cd(0.1)Se. The peak energy of its room temperature near-band-edge photoluminescence is also consistent with this composition. X-ray diffraction pattern and transmission electron microscopy find both types of nanowires to be single crystalline, have the metastable wurtzite structure, and a growth direction along 100. The presence of an Au-Cd-Zn alloy particle at the tip of the nanowires supports vapor-liquid-solid as the growth mechanism. The appearance of constrictions in some of the nanowires is found to be linked to the existence of structural defects, possibly stacking faults, during growth.     

Synthesis of high-purity GaP nanowires using a vapor deposition method

High-purity gallium phosphide (GaP) nanowires were successfully synthesized on the nickel monoxide (NiO) or the cobalt monoxide (CoO) catalyzed alumina substrate by a simple vapor deposition method. To synthesize the high-purity GaP nanowires, the mixture source of gallium (Ga) and GaP powder was directly vaporized in the range of 850–1000 °C for 60 min under argon ambient. The diameter of GaP nanowires was about 38–105 nm and the length was up to several hundreds of micrometers. The GaP nanowires have a single-crystalline zinc blend structure and reveal the core-shell structure, which consists of the GaP core and the GaPO₄/Ga₂O₃ outer layers. We demonstrate that the mixture of Ga/GaP is an ideal source for the high-yield GaP nanowires.     

Synthesis of blue-light-emitting ZnGa2O4 nanowires using chemical vapor deposition

A high-density array of vertically aligned ZnGa(2)O(4) nanowires has been synthesized on Si substrates via CVD of ZnO-Ga at 1000 degrees C consisting of a single-crystalline cubic spinel structure grown in a [111] direction and exhibiting strong photoluminescence and cathodoluminescence in the blue wavelength region.     

Synthesis and characterization of silicon nanowires on mesophase carbon microbead substrates by chemical vapor deposition

Silicon nanowires (SiNWs) have been fabricated by chemical vapor deposition at ambient pressure using SiCl(4) as a silicon source and mesophase carbon microbead powder as a substrate without any templates and/or metal catalysts. The SiNWs have a crystalline core with a very thin amorphous SiO(x) sheath. The obtained SiNWs are homogeneous with average diameters below 50 nm and lengths up to micrometers. Temperature and time effects on the growth of SiNWs were systematically studied. Higher reaction temperatures and longer reaction times resulted in larger diameters and higher yields of SiNWs. SiNWs with a better crystallinity can be obtained at higher temperatures and longer reaction times. The obtained SiNWs were characterized by field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy.     

Large-area graphene single crystals grown by low-pressure chemical vapor deposition of methane on copper

Graphene single crystals with dimensions of up to 0.5 mm on a side were grown by low-pressure chemical vapor deposition in copper-foil enclosures using methane as a precursor. Low-energy electron microscopy analysis showed that the large graphene domains had a single crystallographic orientation, with an occasional domain having two orientations. Raman spectroscopy revealed the graphene single crystals to be uniform monolayers with a low D-band intensity. The electron mobility of graphene films extracted from field-effect transistor measurements was found to be higher than 4000 cm(2) V(-1) s(-1) at room temperature.     

Combinatorial synthesis of carbon nanotubes by the catalytic chemical vapor deposition method

Summary Bimetallic (Fe-Co) catalyst samples prepared from different precursors over various supports were tested in carbon nanotube (CNT) production. In order to quicken the evaluation of the performance of the catalysts a combinatorial arrangement was used.</o:p>     

Metallic Li in carbonaceous nanotubes grown by metalorganic chemical vapor deposition from a metalorganic precursor

Metallic Li in carbonaceous nanostructures was obtained in high concentration (as much as 33.4%) through metalorganic chemical vapor deposition involving certain lithium–aminoalkyl moieties, which are formed in situ , by decomposition of a precursor containing both cobalt and lithium. The bimetallic complex containing both lithium and cobalt was characterized by IR spectroscopy, mass spectroscopy, nuclear magnetic resonance spectroscopy, elemental analysis and thermogravimetric analysis. X‐ray photoelectron spectroscopy measurements performed on the as‐grown films demonstrate that lithium can be stable in metallic form in such a film. Results of X‐ray photoelectron spectroscopic analysis of the as‐grown films are presented as direct evidence of the formation and stabilization of metallic lithium in carbon nanotubes. Carbon nanotubes, encapsulating metallic lithium, can potentially act as a miniaturized nanobattery. Such a battery would be potentially useful in the next generation of communication and remote sensing devices, where a pulse of current is required for their operation. In addition, with metallic lithium, having an effective nuclear magnetic moment, such materials can be envisioned to show potential applications in devices based on nuclear magnetic resonances. Copyright © 2008 John Wiley & Sons, Ltd.     

硅纳米线的化学气相沉积法合成

硅纳米线是近十几年来在纳米科学与技术领域快速发展的一种重要材料．通过精细的结构设计与材料合成,硅纳米线在生物传感、锂离子电池、太阳能电池和光电化学等领域展示出良好的应用前景．化学气相沉积（CVD）法是一大类重要的自下而上合成硅纳米线方法．本文简介了CVD法合成硅纳米线的主要进展,包括具有单一结构和复合结构的硅纳米线的合成．其中,单一结构的硅纳米包括本征（无掺杂）、掺杂和超长的硅纳米线;复合结构的硅纳米线包括轴向异质结、径向异质结、转折结构和树枝状结构的硅纳米线．     

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.     

Ti-Si-N films prepared by plasma-enhanced chemical vapor deposition

Ti-Si-N thin films were deposited on HSS substrates at 560°C using plasmaenhanced chemical vapor deposition. Feed gases used were TiCl₄, SiCl₄, N₂, and H₂. The composition of the films could be controlled well through adjustment of the mixing ratio of the chlorides in the feed gases. The Si content in the film varied in the range of O to 40 at. %. It was jbund that a small addition of Si to a TiN film improved the morphology significantlv, showing dense and glasslike structure. Also a much smootherand more homogeneous interface between thefilm and the substrate was obtained. The Ti-Si- N films containing 10–15 at. % Si showed the maximal microhardness value of about 6350 kgf/mm², much higher than that of TiN films.     

Epitaxial polymerization of 1,3-butadiyne by chemical vapor deposition

1,3-Butadiyne was epitaxially polymerized on the graphite basal plane by chemical vapor deposition to form a homogeneous thin film. The film thickness varied from 100 to 3000 Å depending on the polymerization condition. The films on the graphite showed a variety of interference colors such as blue, purple, or gold depending on the film thickness. Raman spectra revealed that the polymerized film was mainly composed of ? C?C? bonds. Electron diffraction pattern and the ESCA spectrum of the film were quite similar to those of graphite, suggesting that butadiyne was polymerized in an epitaxial manner.     

Formation of metallic Ni nanoparticles on titania surfaces by chemical vapor reductive deposition method

Metallic Ni nanoparticles were successfully prepared on the surface of titania thin film substrate by a novel method, named as chemical vapor reductive deposition (CVRD) method. The growth of the nanoparticles was based on the specific adsorption and heterogeneous nucleation on the surface of substrate, not via vapor-phase formation and subsequent sedimentation. The nanoparticle size was found to be well controllable between 10 and 30 nm by the preparation time and vapor pressure of metal complex precursor. ESCA and electron diffraction results clearly demonstrated Ni nanoparticles as metallic. Titania thin film with metallic Ni nanoparticles on its surface showed high efficiency in their photocatalysis of hydrogen evolution from decomposition of ethanol.     

Controlling the diameter of carbon nanotubes in chemical vapor deposition method by carbon feeding

It was found that the diameter distribution of single-walled carbon nanotubes (SWNTs) grown by the chemical vapor deposition (CVD) method could be controlled by the carbon feeding rate at the growth stage. A unified hypothesis on the relationship between nanoparticle size, growth condition, growth temperature, and diameter of the resulting nanotubes was developed and used to explain the relationship. It was shown that the diameters of SWNTs can be controlled even when highly polydisperse nanoparticles were used as catalyst. Such control enabled us to synthesize uniform small-diameter SWNTs at low carbon feeding rates. Additionally, understanding of the important role of the carbon feeding rate can be used to explain the cause of low growth efficiency in most CVD processes. It would also help us to design methods to improve the growth efficiency of CVD growth of nanotubes.     

Plasma chemical vapor deposition of TiN

Experiments indicate that the temperature in chemical vapor deposition (CVD) of TiN can be decreased from about 1000°C in conventional CVD to about 500°C by the application of a D.C. nonequilibrium plasma. The hardness of the TiN film is greater than 2000 kg/mm² (Vickers). The effect of pressure, ratio of gas mixture, and discharge parameters on the film deposition rate, its hardness, and microstructures has been studied.     

Spatially organized free-standing poly(p-xylylene) nanowires fabricated by vapor deposition

Thin films of poly(chloro-p-xylylene) (PPXC) grown by the pyrolysis and evaporation of chloro-[2.2]paracyclophane in an evacuated chamber contain free-standing, slanted, parallel columns that are 50 mum long and are assemblies of 50- to 100-nm-diameter nanowires, which thus can have an unprecedented aspect ratio as high as 1000:1. The nanostructured thin films organize spatially with a chemical structure similar to that of planar PPXC thin films, but the former also possess nanostructured morphology. Nanostructured thin films of poly(p-xylylene) (PPX) and its derivatives shall be useful as functionalized interfaces for antifouling coatings and biomedical devices.     

Fabrication of graphene with CuO islands by chemical vapor deposition

Graphene prepared on Cu foil by chemical vapor deposition was studied as a function of post growth cooling conditions. CuO islands embedded in the graphene film were discovered and studied by scanning electron microscopy, atomic force microscopy, and X-ray photoemission spectroscopy. It is shown that nanostructured holes can be formed within a graphene film by reduction using hydrogen cooling immediately after film growth. We also observe the formation of symmetrical oxide islands in these holes. This study provides an easy way to fabricate a graphene + CuO composite, and the method may be extended to other graphene based structures.