Polymer-single wall carbon nanotube (SWNT) composite films were prepared and characterized as part of an effort to develop polymeric materials with improved combinations of properties for potential use on future spacecraft. Next generation spacecraft will require ultra-lightweight materials that possess specific and unique combinations of properties such as radiation and atomic oxygen resistance, low solar absorptivity, high thermal emissitivity, electrical conductivity, tear resistance, ability to be folded and seamed, and good mechanical properties. The objective of this work is to incorporate sufficient electrical conductivity into space durable polyimides to mitigate static charge build-up. The challenge is to obtain this level of conductivity (10-8 S/cm) without degrading other properties of importance, particularly optical transparency. Several different approaches were attempted to fully disperse the SWNTs into the polymer matrix. These included high shear mixing, sonication, and synthesizing the polymers in the presence of pre-dispersed SWNTs. Acceptable levels of conductivity were obtained at loading levels less than one tenth weight percent SWNT without significantly sacrificing optical properties. Characterization of the nanocomposite films and the effect of SWNT concentration and dispersion on the conductivity, solar absorptivity, thermal emissivity, mechanical and thermal properties were discussed. Fibers and non-woven porous mats of SWNT reinforced polymer nanocomposite were produced using electrospinning.

In the past, the dispersion of carbon nanotubes (CNTs) in both liquids and solids has been difficult due to the high surface interactions between the tubes. Dispersion of polymer CNT composites is important for such benefits as structural reinforcement of composites, the percolation threshold of CNT based conducting materials, and the thermal properties with the exploitation of the high surface area of CNTs. Here we discuss two approaches towards addressing dispersion of multiwalled nanotubes (MWNTs). One approach is the use of surfactant chemicals selected on the basis that they interact with CNT chemical groups. The second approach is the functionalization through covalent bonding of the CNTs with various polymers including polyethylenimine (PEI), and poly(methyl methacrylate) (PMMA). The two approaches were evaluated to determine whether covalent functionalization was more beneficial than the use of surfactants. Characterization of the dispersion was performed using various microscopy techniques.

The good field-emission properties of carbon nanotubes coupled with their high mechanical strength, chemical stability, and high aspect ratio, make them ideal candidates for the construction of efficient and inexpensive field-emission electronic devices. The fabrication process reported here has considerable potential for use in the development of integrated radio frequency amplifiers or field emission-controllable cold electron guns for field emission displays. This fabrication process is compatible with currently used semiconductor processing technologies. Micropatterned vertically aligned carbon nanotubes were grown on planar Si surface or inside the trenches, using chemical vapor deposition, photolithography, pulsed-laser deposition, reactive ion etching, and the lift-off method. To control the field-emission current by a 3rd electrode, the gate electrode, we grew carbon nanotubes inside the trenches. This triode-type structure is the best to realize the gray-scale carbon nanotube field emission. This carbon nanotube fabrication process can be widely applied for the development of electronic devices using carbon nanotube field emitters as cold cathodes and could revolutionize the area of field-emitting electronic devices such as RF amplifiers and field emission displays.

The magnetic properties of Ce@C82 have been studied. The magnetic anisotropy of Ce@C82 was analyzed taking account of the crystal field of the interior C82 cage acting on Ce3+ ion. Results showed that the reduction of the susceptibility at low temperature was caused due to the antiferromagnetic coupling between Ce3+ ion and C82 cage. The magnetization measurement at several temperatures also supported the antiferromagnetic interaction at low temperature. The magnetic susceptibility larger than the calculated one was measured at higher temperatures due to the magnetic interaction between the metallofullerenes and between the particles in the crystal. The magnetization of some frozen Ce@C82 solutions was found to depend on the applied field magnitude. The dependence suggested that the magnetic anisotropy of Ce ion induced a torque to restrict the rotational motion of Ce@C82 by the field.

We use scanning gate microscopy to precisely locate the gating response in single-wall nanotube devices. Junctions of metallic and semiconducting nanotubes show a dramatic increase in transport current when they are electrostatically doped with holes at the junction. We ascribe this behavior to the turn-on of a reverse biased Schottky barrier. A similar effect is seen in field-effect transistors made from an individual semiconducting single-wall carbon nanotube. In this case, there are two Schottky barriers at the metal contacts, one of which is forward, and one of which is reverse biased. The gating action is only observed at the reverse biased Schottky barrier at the positive electrode. By positioning the gate near one of the contacts, we convert the nanotube field-effect transistor into a rectifying nanotube diode. These experiments both clarify the gating mechanism for nanotube devices and indicate a strategy for diode fabrication based on controlled placement of acceptor impurities at a nanotube field-effect transistor.

The hydrogen adsorption capacity of various carbon nanostructures including single-wall carbon nanotubes, graphitic nanofibers, activated carbon, and graphite has been measured as a function of pressure and temperature. Our results show that at room temperature and a pressure of 80 bar the hydrogen storage capacity is less than 1 wt.% for all samples. Upon cooling, the capacity of hydrogen adsorption increases with decreasing temperature and the highest value was observed to be 2.9 wt. % at 50 bar and 77 K. The correlation between hydrogen storage capacity and specific surface area is discussed.

We report an effective procedure for fabricating carbon nanotube emitters by directly synthesizing carbon nanotubes on an electrochemically sharpened tungsten tip. The nanotubes adhere very well to the tip of tungsten without any painting materials. Thermal cleaning of the tungsten tip under applied electric field reduced the number of nanotubes formed on the tip resulting in a single nanotube emitter. Electron field emission properties were investigated by employing a field emission microscope with a base pressure ~ 1 × 10-9 Torr. The emission images with respect to the applied field and time were obtained. Different emission images consisting of one to four lobes at different applied fields were observed. The characteristic of the emission current vs. applied voltage was analyzed. Applied potentials up to 3000 V were tested. The estimated field on the emitter was on the order of several tens of volts per nanometer. Our investigation suggests that at lower fields, the I-V characteristic of the nanotube emitter follows Fowler-Nordheim (F-N) emission behavior. At higher applied field, current saturation was observed.

We briefly review some methods recently proposed to make films and fibers of preferentially oriented carbon nanotubes. We discuss in more detail a simple spinning process which consists in dispersing the nanotubes in a surfactant solution, re-condensing the nanotubes in the flow of a coagulating polymer solution to form a nanotube mesh, and then collating this mesh to a nanotube fiber. We measure the mechanical properties of the obtained fibers and characterize the nanotube alignment along the fiber axis by X-ray scattering experiments. We show that the alignment can be improved by stretching the fibers under well-defined conditions. This allows the Young's modulus to be increased by a factor 4, leading thereby to materials forty times stronger than high-quality buckypaper. We believe that these improved fibers can already be potentially useful as functional materials. A simple example of electromechanical actuation is shown.

Carbon nanotubes (CNT) possess remarkable physical properties. However, because of their size, they are difficult to handle. Making composites with them gives an alternative way to handle these objects and to make use of their properties at a macroscopic scale. Here, we present a comparative study of the transport properties of PMMA / nanotubes composite films with both SWNTs and MWNTs. At room temperature, the conductivity of the composites follows a pure percolation behavior when increasing the nanotube content. The universal scaling law for random site percolation with a very low percolation threshold (0.3 weight %) is obeyed over two orders of magnitude in CNT content. At low temperature, SWNTs and MWNTs based composites behave differently. While MWNTs composites still obey the percolation law, deviations are observed for SWNTs. The transport properties are discussed in terms of tube-tube contact and charging energy of the tubes.

Our recent achievement of high-yield C60@SWNT synthesis facilitates characterization by various techniques, including selected area electron diffraction (SAD) and Raman spectroscopy. The obtained SAD patterns show that interior C60 molecules sit on a simple 1-D lattice having a parameter of 1.00 nm. Simulated SAD patterns and real-space measurements both support this determination and do not indicate a lattice with a more complex basis, e.g. a dimer basis. Empty and bulk-filled SWNTs (22%, 56%, and 90% yields), each subjected to identical processing steps, were examined by room temperature Raman spectroscopy. Systematic differences are seen between the spectra of filled and unfilled SWNTs, particularly with respect to the G- and RBM-bands of the nanotubes. We present a possible explanation for this behavior.

We have developed a well-controlled method for manipulating carbon nanotubes. The first crucial process involved is to prepare a nanotube array, named nanotube cartridge. We have found the ac electrophoresis of nanotubes by which nanotubes are aligned at the knife-edge. The nanotubes used were multiwalled and prepared by an arc discharge with a relatively high gas temperature. The second important process is to transfer a nanotube from the nanotube cartridge onto a substrate in a scanning electron microscope. Using this method, we have developed nanotube tips and nanotube tweezers that operate in a scanning probe microscope. The nanotube probes have been applied for observation of biological samples and industrial samples to clarify their advantages. The nanotube tweezers have demonstrated their motion in scanning-electron-microscope and operated to carry nanomaterials in a scanning probe microscope.

We employ molecular dynamics to study the effects of ion irradiation on carbon nanotubes lying on different substrates. We show that defect production depends on the type of the substrate and that the damage is higher for metallic heavy-atom substrates than for light-atom substrates, since in the former case sputtered metal atoms and backscattered recoils produce extra damage in the nanotube. We further study the behavior of defects and demonstrate that although ions may severely damage nanotubes in a local region, the nanotube carbon network can heal such a strong localized damage due to defect migration and dangling bond saturation. Finally, we predict the pinning of nanotubes to substrates by forming nanotube-substrate bonds which appear near irradiation-induced defects.

Highly purified single-wall carbon nanotubes (SWCNT) were investigated for use as an anode material for thin film lithium ion batteries. The high purity nanotubes were obtained through chemical refinement of soot generated by pulsed laser ablation. The purity of the nanotubes was determined via thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. The specific surface area and lithium capacity of the SWCNT's was compared to that of other conventional anode materials (i.e., carbon black, graphite, and multi-walled carbon nanotubes). The Brunauer, Emmett, and Teller (BET) technique based on nitrogen adsorption was used to measure the specific surface area of the various anode materials. The SWCNT's exhibited a specific surface area on the order of 915 m2/g, much higher than the other carbonaceous materials. Cyclic voltammetric behavior and the lithium-ion capacity of the materials were measured using a standard 3-electrode electrochemical cell. The cyclic voltammetry showed evidence of “staging” that was similar to other carbonaceous materials. The electrochemical discharge capacity of the purified single walled carbon nanotubes was in excess of 1300 mAh/g after 30 charge/discharge cycles when tested using a current density of 20μA/cm2.

Single-wall carbon nanotubes have been synthesized, purified, attested with a high resolution electron microscopy and Raman scattering and deposited by liquid electrophoresis onto different substrates (including a metallized glass) to produce the effective and homogeneous film cathodes for low-field electron emitters. The emission properties (a threshold of the emission switching on, a current value, a time-stability) of the SWNT cathodes have been investigated. A prototype of a phosphorescent lamp with a nanotube cathode has been designed. The Raman spectra of the SWNT cathode registered in situ from the shining lamp have shown no temperature increase and time-degradation of the nanotube material during the emission process.

To build nanotube based nanodevices, controlling the growth of aligned carbon nanotubes will be essential. Our group reported a method for growing aligned nanotube selectively on SiO2 surfaces by thermal chemical vapor deposition (CVD) method from xylene-metallocene mixtures. Here we will describe further studies on the roles of shape and thickness of patterned oxide structures for the controlled growth of aligned carbon nanotubes. By designing the shapes and the thickness of silicon oxide patterns with conventional micro fabrication techniques like lithography and dry & wet etching we could control the growth position as well as orientation of aligned carbon nanotubes precisely.

Bending induced deformations in single walled carbon nanotubes with zigzag and armchair chirality have been studied computationally using a classical molecular dynamics simulation method. In this the interatomic forces have been described with Brenner's empirical model potential. The results given by this classical model have been assessed by letting the most critical, i.e. the most deformed part, of the nanotube further relax by using a dynamical tight binding simulation method. We find that the empirical potential based approach and the tight binding method reproduce similar deformation patterns when the deformation remains relatively small but at higher levels of deformation the results differ significantly. These comparative simulations indicate that graphene interlayer interaction is an important factor in the behavior of deformed nanotubes.

Apexes of commercial pyramidal silicon scanning microscopy tips were magnetically functionalized by means of local focused electron beam induced deposition. High aspect ratio supertips and local tip coatings with varying apex diameters can be produced by varying exposure time, beam current, and scan mode. The carbonyl precursor Co2(CO)8 was used as source of magnetic metal. Tip performance was tested with magnetic force microscopy (tapping / lift-retrace mode) and magnetically actuated cantilever atomic force microscopy. The deposit contains 34±2 at.% Co, dispersed as 2-5 nm metal nanocrystals in a carbonaceous matrix. Specific surface reactions and Boudouard reactions are proposed to explain the resulting deposit composition measured by Auger spectroscopy. The electrical resistivity is 104 higher than bulk Co resistivity.

We report (6 wt %) storage of H2 at T=77 K in processed bundles of single-walled carbon nanotubes at P=2 atmospheres. The hydrogen storage isotherms are completely reversible. D2 isotherms confirm this anomalous low-pressure adsorption and further reveal the effects of quantum mechanical zero point motion. We propose that our post-synthesis treatment of the sample not only improves access for hydrogen to the central pores within individual nanotubes, but also may create a roughened tube surface with an enhanced binding energy for hydrogen. Such an enhancement is needed to understand the strong adsorption at low pressure. We obtain an experimental isosteric heat qst=125 ± 5 meV for processed SWNT materials.

A binary phase of layered nanotubes, where MWCNs (Multi-walled carbon nanotubes) are coated by WS2, are generated by pyrolysing WO3-coated MWCNs in an H2S/N2 atmosphere at 900 °C. TGA and TEM show that WS2 acts as an antioxidant with respect to the MWCN core.

We report on the structure and electronic properties of single wall carbon nanotubes (SWNTs) tips with atomically spatial resolution. Scanning tunneling microscopy (STM) show topographic images of closed tips with a variety of geometrical structure; these include round, conical, as well as tips with a messy shape. At low bias voltage, topographic STM images show standing wave pattern of the charge density in the vicinity of nanotube ends. The patterns originate from constructive interference between the electronic states and its reflection on the nanotube tips. The modulations extend along 6-8 nm away from the cap. Atomically resolved images show asymmetry in the charge density that smears out as the bias voltage increases. These distinctive tip states do not exist elsewhere on the tube and are related to the presence of topological defects at tube ends.