Large periodic arrays of carbon nanotubes have been grown by plasma-enhanced hot filament chemical vapor deposition on periodic arrays of nickel dots that were prepared by polystyrene nanosphere lithography. A single layer of self-assembled polystyrene spheres was first uniformly deposited on a silicon wafer as a mask, and then electron beam vaporization was used to deposit a nickel layer through the mask. The size of and spacing between the nickel dots are tunable by varying the diameter of the polystyrene spheres, which consequently determines the diameter and site density of carbon nanotubes. The technique can be scaled up at much lower cost than electron beam lithography.

We study the dielectric properties of nanocomposites in the 0–1.5-GHz frequency regime. These composites consist of electrically insulated metallic nanoparticles and carbon nanotubes, the elongated nanostructures in this study, uniformly dispersed in a dielectric matrix. We find that the properties of these composites depend crucially on the shape and monodispersity of the nanoparticles. While at high concentrations the spherical nanoparticles cause only slight modification of the dielectric function of the composite with respect to the matrix, the elongated nanoparticles produce composites with an enhanced real part of the dielectric function and low imaginary part. Our theory, which is in excellent agreement with these results, suggests specific ways to further improve the dielectric properties of the composites.

High quality double-walled carbon nanotubes (DWNTs) were synthesized by decomposition of methane over cobalt (Co) nanoparticles supported on porous MgO nanoparticles. The growth was significantly influenced by catalyst concentration and MgO type. Catalysts with 2.5–5 wt% Co loaded MgO (pore size: ∼4 nm) efficiently grow DWNTs with diameters of 2–4 nm, high graphitization, clean surfaces, and clean inside channels. The preliminary separation of DWNTs from MgO, Co and other carbonaceous nanoparticles has been carried out. Energy dispersive X-ray spectroscopy and X-ray diffraction were employed to analyze the chemical composition of the materials before and after purification.

We demonstrate here that large area periodic arrays of well-aligned carbon nanotubes can be fabricated inexpensively on Ni dots made by the process of self-assembly nanosphere lithography. These periodic arrays appear colorful due to their efficient reflection and diffraction of visible light. In addition, due to their honeycomb lattice structure, these arrays can act as photonic band gap crystals in the visible frequency range. In this report, we present the initial exploration of the optical properties of such arrays. Here we show that these potential 2D photonic band gap crystal arrays might find very important applications in optoelectronics.

Carbon nanotubes (CN-T) have been grown in a honeycomb configuration on silicon substrates using nanosphere self-assembly and plasma enhanced chemical vapor deposition. The optical properties of the arrays were also studied. Diffraction efficiency was found to be a function of the wavelength, angle of incidence and state of polarization of the incident light. The unique optical properties of the arrays combined with the excellent mechanical and electrical properties of carbon nanotubes indicates that these materials may find many uses in the field of optoelectronics. In addition to their optical properties, periodic CNT arrays have a host of other unique electromagnetic and mechanical properties that may be exploited for numerous applications. Polarization measurements indicate that the intensity of both the diffracted light and diffusely scattered light is dependent on wavelength and angle of incidence. These arrays not only reflect and diffract light, but can also have a photonic band gap in, or around, the visible frequency range. The precise frequency location and size of this gap can be controlled by the structural and material parameters of the arrays.

Large-quantity (grams) one-dimensional ZnO nanowires of different sizes have been synthesized by a simple thermal evaporation of ZnO powder in a tube furnace at a temperature controlled to 1000–1200 °C and pressure to 1–2 Torr air. A mixture of ZnO and graphite powder was used as the source. Fine graphite flakes were used to promote the growth. The graphite flakes are the key for large-quantity yield and were easily removed by oxidation in flowing O2 at about 700 °C for 1–3 h. The scanning- and transmission-electron-microscopic studies show that the diameter and length of the nanowires vary from 20 to 100 nm and 0.5 to 10 μm, respectively. Room temperature photoluminescence studies found that the luminescent intensity depends on the processing conditions. A reduced band edge ultraviolet (380 nm) and deep-band green (520 nm) emission have been observed for these nanowires. Most importantly, the method can be extended to any other oxide nanowires that will be the building block of future nanoscale devices.

Carbon nanotubes were investigated as high-performance reinforcement for polymer composites. The inherently superior mechanical properties of nanotubes coupled with the high interfacial surface areas available to dissipate energy suggest that nanotube-polymer composites would have excellent potential as high-strength, impact-resistant materials. The multiwall carbon nanotubes (MWNT) produced by arc and chemical vapor deposition and the double-walled nanotubes (DWNT) produced by the arc process were investigated as reinforcement in polycarbonate thermoplastic. The as-grown non-polar nanotubes did not disperse readily in high molecular weight polycarbonates. However, a significant increase in compressive strength was achieved by using uniformly dispersed nanotubes in low molecular weight polycarbonate and also in an optimum ratio of low and high molecular weight polycarbonate. The compressive strength enhancement for the same polymer matrix by the different nanotubes is dependent on the nanotube's purity, the inherent properties (strength and dimension) of the nanotubes, and polymer compatability.

. The effect of pure nickel, iron and cobalt on growth of aligned carbon nanotubes was systematically studied by plasma-enhanced hot-filament chemical vapor deposition. It is found that the catalyst has a strong effect on the nanotube diameter, growth rate, wall thickness, morphology and microstructure. Ni yields the highest growth rate, largest diameter and thickest wall, whereas Co results in the lowest growth rate, smallest diameter and thinnest wall. The carbon nanotubes catalyzed by Ni have the best alignment and the smoothest and cleanest wall surface, whereas those from Co are covered with amorphous carbon and nanoparticles on the outer surface. The carbon nanotubes produced from Ni catalyst also exhibit a reasonably good graphitization. Therefore, Ni is considered as the most suitable catalyst for growth of aligned carbon nanotubes.

We have successfully fabricated many freestanding carbon nanotube arrays on silicon substrates. Two sizes of nickel dot arrays have been made by E-beam lithography. It has been found that the size of the carbon nanotubes is closely related to the size of the dot. Compared with our previous report on diameters of about 300–400 nm, much thinner carbon nanotubes of 100–150 nm have been made. With even smaller dots, it is expected that even thinner nanotubes of a few tens of nanometers could be made. The nanotube height is controlled by the growth time and nanotube uniformity has been greatly improved by introduction of a two-phase process of nucleation and growth.