We have grown well-aligned carbon nanotube arrays by thermal chemical vapor deposition at 800°C on Fe nanoparticles deposited by a pulsed laser on a porous Si substrate. Porous Si substrates were prepared by the electrochemical etching of p-Si(100) wafers with resistivities of 3 to 6 ωcm. These well-aligned carbon nanotube field emitter arrays are suitable for electron emission applications such as cold-cathode flat panel displays and vacuum microelectronic devices like microwave power amplifier tubes. Field emission characterization has been performed on the CNT-cathode diode device at room temperature and in a vacuum chamber below 10−6 Torr. The anode is maintained at a distance of 60[.proportional]m away from the carbon nanotube cathode arrays through an insulating spacer of polyvinyl film. The measured field emitting area is 4.0×10−5cm2. Our carbon nanotube field emitter arrays emit 1mA/cm2at the electric field, 2V/[.proportional]m. And they emit a large current density as high as 80mA/cm2 at 3V/[.proportional]m. The open tip structure of our carbon nanotubes and their good adhesion through Fe nanoparticles to the Si substrate are part of the reason why we can attain a large field emission current density within a low field. The field emitter arrays in our diode device are vertically well-aligned carbon nanotubes on the Si-wafer substrate.

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.

We report calculation of the NMR chemical shift anisotropy (CSA) tensor →μ of single-wall carbon nanotubes, within the London approximation (ring currents contribution). Our results indicate that the isotropic line as measured by high resoultion experiments is splited about 11ppm between metallic and semiconductor nanotubes. We carefully check that this result remains vaild and observable when the bundle packing is taken into account. The resulting broadening is aroune 20ppm, but reduces onto a sharp lorentzian (<1ppm) when averaging by high resoultion NMR measurements.

A hot filament chemical vapour deposition (HF-CVD) process was used to synthesise nitrogenated carbon (C:N) nanotubes characterised by feather-like decoration of the tube surface. As a function of deposition temperature the diameter of the produced tubular structures could be adjusted in a controlled way ranging from 1 µm to 50 nm. The influence of catalysts was demonstrated comparing the morphology of catalytically grown tubes with tubes grown onto pure Si wafers. High resolution TEM reveals that the nanotubes are hollow with a wall structure consisting of inner ordered walls and an outer more disordered surface. A possible growth mechanism will be discussed. Furthermore, field emission in vacuum was studied and showed a spectacular correlation to the deposition temperature and therefore the diameter of the C:N tubes.

Raman spectra for three SWNT samples doped with Br2 were studied using different excitation energies, 2.41 eV and 1.58 eV. One sample was also studied under high pressure up to 2 GPa. The vibrations in the low frequency range behave similarly for all samples. With an excitation energy of 1.58 eV, additional peaks at ca 240 cm−1 and 209 cm−1 are observed. With increasing pressure, the peak at 209 cm−1 gradually softens by 2∼3 cm−1 and becomes very weak at 1.7 GPa, while a new broader peak at ca 250 cm−1 remains constant up to 2 GPa. A number of high intensity overtone modes are observed under high pressure. These results indicate that the vibrations are attributed to bromine, not to the breathing modes of SWNTs, and that bromine resides in the bundles, possibly also inside tubes as a form of polymer.

Carbon single-wall nanotubes (SWNTs) have a variety of unique physical, electronic and mechanical properties. However, the SWNTs must be thoroughly purified if they are to be used in the wide array of projected applications and basic studies. Although numerous purification schemes have been employed in the literature, none of them provides an accurate estimate of the SWNT content in the final materials. Here we describe a simple 3-step purification process coupled to an accurate method for determining SWNT wt.% contents in both the crude and purified samples. We employ a laser vaporization synthesis technique and take care to avoid both forming graphite-encapsulated metal particles and incorporating sputtered target material into the collected soot. It is then possible to employ a dilute nitric acid reflux to digest the metal particles and to functionalize and redistribute the non-nanotube carbon fractions in the soots forming a uniform and reactive coating on the SWNTs. This coating is selectively removed by oxidation in air at 550 °C. Thermogravimetric analysis (TGA) and inductively coupled plasma spectroscopy (ICPS) are used to evaluate the purity of the material at each step of the process, and illustrate that the crude materials contain 6 wt.% metal and 10-35 wt.% SWNTs. The purified materials are found to be >98 wt.% pure with metal contents of < 1 wt.%. Using the 98 wt.% pure materials as a yardstick, we are able to evaluate the accuracy of several other methods commonly employed in determining nanotube purity levels including transmission and scanning electron microscopies (TEM and SEM) and Raman spectroscopy. We show that determining nanotube contents in various materials requires careful scrutiny and the application of multiple techniques.

Single wall carbon nanotube (SWNT) doped by alkali-metals are investigated by Raman scattering. For saturation-doped compounds, the most striking intrinsic features are two low-frequency peaks assigned to modes involving both radial motions of tubes and alkali-atoms vibrations. On the other hand, the evolution of the Raman spectra with doping was studied in-situ. Two different stable phases are identified and associated to distinct organizations of the tubes and of the alkali-atoms.

The carbon nanotubes were grown on the round Ni particles at the growth temperature below 60 °C by the radio frequency plasma CVD equipment from the acetylene and the hydrogen gases. For the low growth of the carbon nanotubes, the acetylene concentration in the hydrogen gas was essential parameter. In the case of the high acetylene concentration above 30 %, the cauliflower-like carbon film was grown. On the other hand, the low acetylene concentration of 10 % realized the low temperature growth of the carbon nanotubes.

Atomistic simulations are used to better understand the behavior of bundles of single- walled carbon nanotubes that have been placed between two sliding diamond surfaces. A many-body reactive empirical potential for hydrocarbons that has been coupled to a Lennard-Jones potential is used to determine the energies and forces for all the atoms in the simulations. The results indicate that the degree of compression of the nanotube bundle between the nanotubes has a significant effect on the responses of the nanotubes to shear forces. However, no rolling of the nanotubes is predicted in contrast to previous studies of individual nanotubes moving on graphite.

We have described a novel experimental technique to separate nanotubes from other unwanted carbon species in arc generated carbon soot. A conjugated polymer was used to bind to nanotubes in solution. The resultant hybrid was soluble while extraneous carbon material formed a sediment at the bottom of the sample bottle. This process was monitored using electron paramagnetic resonance (EPR) which showed that 63% of nanotubes were kept in solution while 98.1% of impurities were rejected. Optimal polymer characteristics for nanotube solubility were identified using geometry optimisation and experimental evidence. It was calculated that a successful polymer has a flat shaped helical backbone with solvent solubilising groups projected outwards. This is achieved with the following polymer characteristics, two solvent solubilising groups on a twist allowing π-conjugated backbone.

Boron nitride nanotubes (BN-NTs) were synthesized in “mass” quantities (∼0.6 g/h) using a continuous CO2 laser ablation reactor described in the literature [1]. High-resolution electron microscopy (HRTEM) analyses have shown the nanotubes to be organized in “ropes” comprising ∼10 tubes. Analysis of HRTEM images indicate that the majority of the tubes are zig-zag. The chemical composition of the tubes was confirmed using electron energy loss spectroscopy (EELS) analysis, which also determined that nanoparticles terminating tube ends were composed of pure boron covered by BN fullerene-like “cages”. The growth mechanism of the nanotubes seems to be “root-based” with tubes growing from boron nanoparticles dispersed throughout the samples; the non-particle-terminated ends of the tubes exhibit flat “caps” characteristic of BN-NTs [2].

13C nuclear magnetic resonance on functionalized single wall carbon nanoutubes is reported. We present a possible chemical modification of the nanotube in order to get soluble materials. NMR is used in order to study in details the chemical changes and their reversiblities. In particular, acid groups, inequivalent sp2 and sp3 carbons attributed to functionalized nanotubes are identified and characterized.

We report on the structural analysis of multiwall carbon nanotubes (MWNTs), produced by DC arc discharge in hydrogen gas, using a scanning tunneling microscope operated at ambient conditions. On a microscopic scale the images show tubes condensed in ropes as well as individual tubes which are separated from each other. Individual nanotubes exhibit various diameters (2.5-6 nm) and chiralities (0-30Å). For MWNTs rope, the outer portion is composed of highly oriented nanotubes with nearly uniform diameter (4-5 nm) and chirality. Strong correlation is found between the structural parameters and the electronic properties in which the MWNTs span the metallic-semiconductor regime. True atomic-resolution topographic STM images of the outer shell show hexagonal arrangements of carbon atoms that are unequally visible by STM tip. This suggests that the stacking nature of MWNTs, may effect the electronic band structure of the tube shells. Unlike other MWNTs produced by arc discharge in helium gas, the length of the tubes are rather short (80-500 nm), which make it feasible to use them as a components for molecular electronic devices.

High-resolution transmission electron microscopy (HRTEM) study of heavily fluorinated carbon nanofibers was performed under an ultra high voltage transmission electron microscope (UHVTEM). TEM observation showed rapid transformation of the disordered structure of fluorinated nanofiber to the cylindrical layer structure that is same as the non-fluorinated nanofiber. This observation suggests that electron beam irradiation helps fluorine atoms to dissociate from the carbon atoms. Li-ion secondary battery test cell using fluorinated nanofibers was prepared and the battery performance was tested as a function of cycling.

The low frequency RBM observed in SWNTs has been proved to probe efficiently their diameter distribution. We have built a model to estimate the interactions between individual nanotubes when arranged in bundles which leads to a RBM upshift of 10 to 20 cm−1. In a PMMA-SWNTs composite, our model shows that an upshift can be also predicted as due to the stress applied by the polymer on the bundles upon breathing. Finally, the interaction between concentric layers in MWNTs can lead to low frequency modes originating from the RBM of individual tubes as observed experimentally.

Multi-Walled Carbon Nanotubes (MWNTs) mounted on commercial Scanning Force Microscopy (SFM) cantilevers have proven to be excellent probes for high resolution Tapping Mode-Scanning Force Microscopy (TM-SFM). Because of their robust nature and high electrical conductance, MWNTs are also attractive for use in Conductive Probe-Scanning Force Microscopy (CP-SFM). To be used in this application, however, the MWNT must be mounted via a high conductance contact to a conductive cantilever. A technique has been developed that produces such a contact. First, a MWNT is attached using acrylic adhesive to a commercial SFM cantilever that has been vacuum coated with gold. Then, a cap of gold is deposited over the junction between the MWNT and the SFM cantilever via spatially selective electro-deposition.

Carbon, silicon nitride and boron nitride nanostructures were synthesized using microwave plasma enhanced chemical vapor deposition. Both scanning and transmission electron microscopies and x-ray diffraction were used to observe the morphology and structures while energy dispersive x-ray was used to determine the composition of the nanostructured materials. Bamboo-like multiwalled carbon nanotube structures were observed while silicon nitride showed novel needle-like solid structures. All materials were deposited using a thin film iron catalyst seeded on either silicon with reactive plasma gases containing either a mixture of methane and ammonia or ammonia. A general discussion of the nucleation and growth mechanisms for the various materials will also be included.

A summary of our recent work related to the growth of carbon nanotubes (CNTs) inside the pores of anodized alumina oxide (AAO) films is presented. The surface topography of the AAO film was studied by atomic force microscopy, while the internal pore structure of the AOO templates was concluded from the shape of the CNTs obtained. The effect of the different experimental approaches and of the anodization voltage value on the features of the pores and CNTs is also discussed, as well as the catalytic effect in the acetylene pyrolysis of the Co particles and internal alumina walls. The CNTs wall structure observed by HRTEM and its implication on some physico-chemical properties of the CNTs are also presented.

Quantum transport properties of intermolecular nanotube contacts are investigated. We find that atomic structure in the contact region plays important roles and resistance of contacts varies strongly with geometry and nanotube chirality. Nanotube end-end contacts have low resistance and show negative differential resistance (NDR) behavior. Exerting small pressure/force between the tubes can dramatically decrease contact resistance, if the contact is commensurate. Significant variation and nonlinearity of contact resistance may lead to new device applications.

The synthesis and characterisation of one-dimensional (1D) crystals that have a well-specified chemistry, size and crystal structure have presented a formidable challenge for materials chemistry and analysis. We report here the filling of single (SWNTs) and double walled carbon nanotubes (DWNTs) by two different p-block halides, TlCl and PbI2. The nanotubes were produced either by the arc synthesis [1] or by a CVD method [2], based on the reduction of a Mg0.9Co0.1O solid solution by a hydrogen-methane mixture. In the case of TlCl, the structure of the crystals observed inside the tubes were all found to be derived from the rocksalt form and bilayer crystals were observed which exhibited reduced coordination relative to the fcc structure, as determined from high resolution transmission electron microscopy (HRTEM). In contrast, the crystal structure of bulk TlCl is a CsCl type structure. These results are consistent with the recently reported reduced coordination KI crystals formed within SWNTs [3]. In the case of PbI2 (i.e. with the CdCl2 structure), the use of HRTEM images combined with image simulations was used to confirm the partially reduced coordination of Pb atoms within the SWNT and DWNT confined 1D crystals.