Hybrid nanostructures consisting of tungsten oxide nanorods with mushroom-shaped carbon caps were grown on electrochemically etched tungsten tips by thermal chemical vapor deposition with methane and argon. These nanorods grow along the radial direction and are very straight and smooth. Electron microscopy revealed a dominant diameter and length of approximately 50 nm and approximately 0.6 microm, respectively. High-resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS) revealed the presence of crystalline monoclinic W18O49 in the nanorods, and the cap was entirely amorphous carbon. A plausible growth mechanism involves the reduction of tungsten oxide WO3, present on the tungsten surface, by methane at 900 degrees C.

Fluorescent beads were excited by a laser beam coupled through a multiwalled carbon nanotube array. The images of the fluorescent beads showed a distinctive dependence on the polarization direction of the laser beam owing to the surface plasmons induced from the metallic property of the array. The thickness of the array is 2 mu m as compared to the metallic films of tens of nanometers in thickness that are conventionally used for surface plasmon excitation. This remarkable photon coupling capacity of a multiwalled carbon nanotube array is attributed to the confinement of electrons in its outermost tube shells and ballistic transport. (C) 2005 American Institute of Physics.

Nitrogen substitution reaction in a graphene sheet and carbon nanotubes of different diameter are investigated using the generalized tight-binding molecular dynamics method. The formation of a vacancy in curved graphene sheet or a carbon nanotube is found to cause a curvature dependent local reconstruction of the surface. Our simulations and analysis show that vacancy mediated N substitution (rather than N chemisorption) is favored on the surface of nanotubes with diameter larger than 8 nm. This predicted value of the critical minimum diameter for N incorporation is confirmed by experimental results presented on nitrogen-doped multiwalled nanotubes with approximate to5 at. % nitrogen prepared by the thermal chemical vapor deposition process.

Schottky contacts were fabricated on composites of high molecular weight polyaniline and pristine multiwalled carbon nanotubes. Physical and electrical characteristics of these organic composite materials were studied by using atomic force microscopy (AFM), scanning electron microscopy (SEM), and electrical measurements. The RMS surface roughness of the composite films was found to be 4 nm. From the IV characteristics of these composite devices, it appears that the current follows Ohm's law at lower voltages and Child's law at higher voltages, indicating a space-charge-limited emission mechanism in the presence of a distribution of shallow traps.

Mechanical and electrical properties of high molecular weight polyaniline/ multiwalled carbon nanotube composite films were investigated. Addition of carbon nanotubes to polyaniline films was accomplished by solution processing. Physical characterization of these composites by thermogravimetric analysis, tensile testing, dynamic thermal mechanical analysis, and atomic force microscopy measurements indicate that polyaniline containing 1% carbon nanotubes is more mechanically and thermally stable than neat polyaniline. Rectifying aluminum contacts were fabricated using this composition of the composite material, along with neat polyaniline for comparison. The measured electrical characteristics indicate that the current levels of the polyaniline/ carbon nanotube composite devices are nearly an order of magnitude higher than those of the polyaniline devices; thus, this composite material has the potential for applications in organic electronics. (C) 2004 The Electrochemical Society.

Lithium insertion (deinsertion) into ( from) chemically etched multi-walled carbon nanotubes (c-MWNTs) has been investigated using various electrochemical techniques such as chronopotentiometry, chronoamperometry, and electrochemical impedance spectroscopy. The results indicate that not only the reversible capacity but also the rate capability was improved by a chemical etching ( shortening) of the nanotubes. The observed enhancement in capability at high-rate lithium insertion/deinsertion is attributed to the increased electrochemically active area and reduced lithium diffusion length along the nanotubes, resulting from the structural defects and open ends of the c-MWNTs.

High molecular weight polyaniline / multi-walled carbon nanotube composite films were fabricated using solution processing. Composite films with various weight percentages of multiwalled carbon nanotubes were fabricated. Physical properties of these composites were analyzed by thermogravimetric analysis, tensile testing, and scanning electron microscopy. These results indicate that the addition of multiwalled nanotubes to polyaniline significantly enhances the mechanical properties of the films. In addition, metal–semiconductor (composite) (MS) contact devices were fabricated, and it was observed that the current level in the films increased with increasing multiwalled nanotube content. Furthermore, it was observed that polyaniline containing one weight percent of carbon nanotubes appears to be the most promising composition for applications in organic electronic devices.

Photoinduced phenomena are of general interest for new materials. Recently, photoinduced molecular desorption of oxygen has been reported in carbon nanotubes. Here we present, using thermopower measurements, that carbon nanotubes when exposed simultaneously to UV light and oxygen exhibit photoinduced oxidation of the nanotubes. At least two plausible mechanisms for the experimentally observed photoinduced oxidation are proposed: (i) a lower energy barrier for the adsorption of photo-generated singlet oxygen, or (ii) due to the presence of defects in carbon nanotubes that may facilitate the formation of locally electron-deficient and electron-rich regions on the nanotubes which facilitate the adsorption of oxygen molecules on the nanotubes.

We have previously shown that high-purity multiwalled carbon nanotubes (pristine MWNTs) can be prepared from a mixture of xylene-ferrocene (99 at% C:1 at% Fe) inside a quartz tube reactor operating at approximately 700 degrees C. In a similar process, approximately 3 g of melamine (C3H6N6) was introduced during the growth of MWNTs to prepare nitrogen-doped nanotubes. The structural and electronic properties of nitrogen-doped MWNTs were determined by scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and thermopower measurements. The individual nitrogen-doped nanotube exhibits a bamboo-like structure and comprises 6-16 tube walls, as evidenced by HRTEM studies. The EELS measurements yielded an average nitrogen content of approximately 5 at% in the doped tubes. The thermoelectric power data of nitrogen-doped MWNTs remained negative even after exposure to oxygen for an extended period of time, suggesting that nitrogen doping of MWNTs renders them n-type, consistent with scanning tunneling spectroscopic studies on similar nanotubes.

Composites of high molecular weight polyaniline and carbon nanotubes are investigated for electronic device applications. Physical characterization by Thermogravimetric analysis and atomic force microscopy indicates that polyaniline containing 1% Carbon Nanotubes is suitable for organic devices. Measured electrical characteristics of Schottky diodes fabricated using these materials exhibit current levels in the polyaniline/carbon nanotube composite devices nearly an order of magnitude higher than in the polyaniline devices.

Multiple-walled carbon nanotubes (MWNTs) produced using the chemical vapor deposition method were functionalized via attaching aminopolymer poly(propionylethylenimine-co-ethylenimine) to the nanotubes. Two different reaction conditions based on acylating the nanotube-bound carboxylic acids and on directly heating nanotubes in the polymer melt were used and compared. Both methods were effective in the nanotube functionalization, and the polymer-attached MWNTs were found to be soluble in many common organic solvents and in water. Results from the characterization of the functionalized nanotube samples using electron microscopy, optical spectroscopy, NMR, and thermal analysis techniques are presented and discussed.

Various electrochemical techniques have been used to study the electrochemical insertion (extraction) of lithium into (from) multi-walled carbon nanotubes (MWNTs) prepared by catalytic decomposition of ferrocene and xylene. The galvanostatic charge/discharge profiles display a small hysteretic loss and the cyclic voltammograms are quite symmetric in the shape of cathodic and anodic branches, implying that lithium insertion/extraction process is highly reversible. In addition, rate capability and cycleability of charge into the MWNTs are satisfactory. The excellent reversibility and small hysteretic loss of the MWNT are attributed to the extremely pure structural character of the MWNTs with moderate chemical diffusion coefficient of lithium through the structure.