Encapsluation of Co and Pd multi-metal nanowires inside multiwalled carbon nanotubes by microwave plasma chemical vapor deposition

We report the synthesis of multiwalled carbon nanotubes (MWCNTs) encapsulated with Co/Pd magnetic and nonmagnetic multi-metal nanowires using Co and Pd thin-layers deposited on Si substrate by microwave plasma enhanced chemical vapor deposition using a bias-enhanced growth method. Detailed structural and compositional investigations of these metal nanowires inside MWCNTs were carried out by scanning electron microscopy and transmission electron microscopy to elucidate the growth mechanisms. Energy dispersive X-ray spectroscopy revealed that MWCNTs were encapsulated with Co and Pd nanowires, separately, at the tube top and the bottom of Co nanowire, respectively. The face-centered-cubic (fcc) structure of Co nanowires was confirmed by a selected area diffraction pattern. We proposed a fruitful description for the encapsulating mechanisms of both Co and Pd multi-metal nanowires. © 2006 Elsevier B.V. All rights reserved.

SiO2 coating of silver nanoparticles by photoinduced chemical vapor deposition.

Gas-phase silver nanoparticles were coated with silicon dioxide (SiO2) by photoinduced chemical vapor deposition (photo-CVD). Silver nanoparticles, produced by inert gas condensation, and a SiO2 precursor, tetraethylorthosilicate (TEOS), were exposed to vacuum ultraviolet (VUV) radiation at atmospheric pressure and varying temperatures. The VUV photons dissociate the TEOS precursor, initiating a chemical reaction that forms SiO2 coatings on the particle surfaces. Coating thicknesses were measured for a variety of operation parameters using tandem differential mobility analysis and transmission electron microscopy. The chemical composition of the particle coatings was analyzed using energy dispersive x-ray spectrometry and Fourier transform infrared spectroscopy. The highest purity films were produced at 300-400 degrees C with low flow rates of additional oxygen. The photo-CVD coating technique was shown to effectively coat nanoparticles and limit core particle agglomeration at concentrations up to 10(7) particles cm(-3).

Numerical simulation of the growth of ZnO nanostructures in a tube furnace by physical vapour deposition

Zinc oxide is a versatile II-VI naturally n-type semiconductor that exhibits piezoelectric properties. By controlling the growth kinetics during a simple carbothermal reduction process a wide range of 1D nanostructures such as nanowires, nanobelts, and nanotetrapods have been synthesized. The driving force: for the nanostructure growth is the Zn vapour supersaturation and supply rate which, if known, can be used to predict and explain the type of crystal structure that results. A model which attempts to determine the Zn vapour concentration as a function of position in the growth furnace is described. A numerical simulation package, COMSOL, was used to simultaneously model the effects of fluid flow, diffusion and heat transfer in a tube furnace made specifically for ZnO nanostructure growth. Parameters such as the temperature, pressure, and flow rate are used as inputs to the model to show the effect that each one has on the Zn concentration profile. An experimental parametric study of ZnO nanostructure growth was also conducted and compared to the model predictions for the Zn concentration in the tube. © 2008 Materials Research Society.

Gas-phase production of multifunctional composite nanoparticles by photoinduced chemical vapor deposition

As these results indicate, photo-CVD coating is a robust process that allows for the creation of core-shell nanoparticles. In the present work we demonstrated that photo-CVD can effectively coat Fe2O3 particles with silica for purposes of biological applications. TDMA results combined with TEM images indicate that all particles are effectively coated and that particle coating thicknesses can be tuned to desired thickness depending on the application. In addition, the ability to vary coating properties and to coat high concentrations of particles makes this technique of interest for industrial production where uniform properties are needed for large quantities of particles [2]. Copyright © 2010 by ASME.

Cold-gas chemical vapor deposition to identify the key precursor for rapidly growing vertically-aligned single-wall and few-wall carbon nanotubes from pyrolyzed ethanol

Vertically-aligned carbon nanotubes (VA-CNTs) were rapidly grown from ethanol and their chemistry has been studied using a "cold-gas" chemical vapor deposition (CVD) method. Ethanol vapor was preheated in a furnace, cooled down and then flowed over cobalt catalysts upon ribbon-shaped substrates at 800 °C, while keeping the gas unheated. CNTs were obtained from ethanol on a sub-micrometer scale without preheating, but on a millimeter scale with preheating at 1000 °C. Acetylene was predicted to be the direct precursor by gas chromatography and gas-phase kinetic simulation, and actually led to millimeter-tall VA-CNTs without preheating when fed with hydrogen and water. There was, however a difference in CNT structure, i.e. mainly few-wall tubes from pyrolyzed ethanol and mainly single-wall tubes for unheated acetylene, and the by-products from ethanol pyrolysis possibly caused this difference. The "cold-gas" CVD, in which the gas-phase and catalytic reactions are separately controlled, allowed us to further understand CNT growth. © 2012 Elsevier Ltd. All rights reserved.

Chemical vapor deposition of nanocrystalline graphene directly on arbitrary high-temperature insulating substrates

Large area uniform nanocrystalline graphene is grown by chemical vapor deposition on arbitrary insulating substrates that can survive ∼1000°C. The as-synthesized graphene is nanocrystalline with a domain size in the order of ∼10 nm. The material possesses a transparency and conductivity similar to standard graphene fabricated by exfoliation or catalysis. A noncatalytic mechanism is proposed to explain the experimental phenomena. The developed technique is scalable and reproducible, compatible with the existing semiconductor technology, and thus can be very useful in nanoelectronic applications such as transparent electronics, nanoelectromechanical systems, as well as molecular electronics. © 2012 IEEE.