The growth of silicon nanotubes (SiNTs) by a dual-RF-plasma treatment technique is reported here. These SiNTs are vertically aligned and self-assembled from Si substrates at 500 degree Celsius by the use of Cu catalysts. Their diameters are ∼50 to 80 nm with tubular wall thickness of ∼10-15nm. Cu vapors were found partially filled inside the SiNTs. This is a novel technique that can convert bulk materials into their nanostructures.

The free electron laser (FEL) of 450 or 500 nm was irradiated onto the pressed C60 powder in vacuum. The grains with μm-order were observed showing the colors of blue, purple, yellow, and white in optical microscope images. The Ag(2) derived mode around 1460 cm−1 in Raman spectra was observed from the grain, indicating the polymerization. The 100 μm-length grain was obtained just after dissolving the FEL irradiated specimens into the toluene and evaporating it. In order to expand the scale of C60 polymer grains and to obtain an amorphous C60 polymer, the FEL irradiation was carried out in solution to reduce the directivity for polymerization. Although polymerization was not promoted in C60 precipitation in supersaturated solution due to low density of C60, the precipitation grown with the liquid-liquid interfacial precipitation (LLIP) method showed the 1454 cm−1 Ag(2) derived mode in addition to the peaks around 1460 cm−1 in toluene. In m-xylene with LLIP method, in a whole area of C60 pillar-grains, polymerization was confirmed by the Raman analysis.

Molecular dynamics (MD) studies are carried out to investigate the electron irradiation damages in carbon nanomaterials. The interaction between an incident electron and a carbon atom is modeled based on the Monte Carlo method using the elastic scattering cross section. The electron irradiation damages in graphen, graphite, single-walled carbon nanotube (SWNT) and carbon nanopeapod are demonstrated. The cross-links among the nanostructures caused by the knock-on effect are observed as typical damages. The dependence of the damages on the electron primary energy is also shown for the SWNT.

We report the effect of CO2 addition to CO4 gas on carbon nanotube (CNT) growth by chemical vapor deposition. CO2 gas was introduced during the growth of CNTs on Fe0.05Mo0.025MgO0.925 and Ni0.05Mo0.025MgO0.925 catalysts by CO4 gas at a temperature of 800–850°C, and its concentration in a fraction of the gas flow rate was varied from 5×10−3 to 50%. In the experimental condition of the preferential growth of multi-walled CNTs, the carbon yield and the G/D ratio in the Raman spectra of the CNTs grown in 10%-CO2/CO4 were slightly higher than that grown in CO4 only. However, CNTs hardly grew when the CO2 concentration was more than 10%. We then prepared CO2 gas diluted with Ar gas (CO2/Ar) and varied its flow rate between 0 and 10 sccm. As the CO2/Ar gas flow rate was increased, the number of RBM peaks decreased even though the G/D ratio gradually decreased. The decrease in the RBM intensities of CNTs on the FeMoMgO catalyst was more significant than that of NiMoMgO.

It has been reported that carbon nanotubes (CNTs) were formed through the decomposition of SiC(000-1) surfaces by heating in a vacuum. By this growth technique, well aligned zigzag-type CNTs can be selectively formed without any catalysts and the diameters of the CNTs are fairly uniform. Moreover, this growth technique has an advantage in fabrication of CNT devices, since CNTs grow into the inside of SiC, facilitating the application of semiconductor process. So far, we have reported that ambient oxygen enhances the CNT growth rate [1]. However, the optimum oxygen pressure has never been investigated enough. It has also been reported that SiO2 layer is formed on SiC surface after annealing under high oxygen pressure [2]. In this study, we investigated the relation between surface oxide formation and CNT growth under various annealing conditions. After HF etching, 6H-SiC(000-1) (Carbon-face) samples were introduced into an ultra-high vacuum (UHV) chamber and annealed at various temperatures between 800 and 1250°C. During the annealing, oxygen partial pressure was controlled by supply of oxygen gas. The oxygen pressure was set between 10-4 and 1 Pa. For comparison, we also annealed several samples under UHV (10-6 Pa). Scanning tunneling microscopy (STM) observation and X-ray photoelectron spectroscopy (XPS) measurements were carried out to analyze their surface structures and chemical species. It was observed that the surface decomposition of SiC had occurred after annealing at 800°C under UHV, and carbon nanocaps were formed on the SiC surface at 1200°C, which subsequently transformed into CNTs. When oxygen pressure was below 10-2 Pa, the nanocap formation was observed between 1150 and 1200°C irrespective of oxygen pressure. However, at 1 Pa of oxygen pressure, SiO2 layer was observed on the SiC surface after annealing at 1200°C and no carbon nanocaps were observed. These results indicate that it is necessary to anneal SiC below 1 Pa to form CNT, although the presence of oxygen enhances CNT formation below 10-3 Pa. The boundary between the active oxidation and the passive oxidation in SiC oxidation estimated from our results was well consistent with previous studies for SiC oxidation under higher oxygen pressure (>1 Pa)[2]. From our results, in order to grow CNT effectively, it is important to minutely control oxygen pressure.

Clay particles were used to facilitate the dispersion and network formation of single-walled carbon nanotubes (SWNTs) in an epoxy matrix. In the presence of clay, electrical conductivity increase and percolation threshold reduction for SWNT/epoxy composites were achieved simultaneously. These improvements are due to better SWNT dispersion, as evidenced by optical microscopy and scanning electron microscopy. Dynamic mechanical analysis (DMA) shows that mechanical properties of the composites without clay could be improved by clay addition. SWNTs appear to have an affinity for clay that causes them to become more exfoliated and better networked.

We have successfully grown carbon nanotubes (CNTs) by alcohol plasma-enhanced chemical vapor deposition (PECVD). When 0.01 wt% ferrocene was added to alcohol, vertically-aligned CNTs could be grown using RF (= 13.56 MHz) plasma at 650°C. In contrast, no CNTs were obtained by pure alcohol PECVD. To understand the plasma properties for CNT growth, especially plasma species containing a gas phase of alcohol plasma, we analyzed the plasma using optical emission spectroscopy (OES) and quadrupole mass spectrometry (QMS). From the OES measurement, one could identify the emission peaks from the excitation states of CHO, CO, C2, O2, H, CH+, and H2O+, while the QMS measurement also showed the existence of CO, H2O, and CxHy (x≥2, y≥2). It is considered that such plasma species affect CNT growth by changing the oxidation state of the catalyst or by adjusting the amount of precursor species in the plasma. Comparing this PECVD experiment with thermal alcohol CVD (without plasma), only PECVD can be used to grow CNTs under the reported experimental conditions. It is considered that thermal alcohol CVD requires more energy to grow CNTs because 650°C is a little lower than the temperature required for CNT growth. These results indicate that in alcohol plasma, the active species produced by decomposition and recombination reactions have a possibility to promote/suppress CNT growth depending on the process conditions.

Plasma-enhanced chemical vapor deposition (PECVD) is recognized as one of the viable fabrication techniques of carbon nanotubes (CNTs). However, “CNTs” synthesized in low-pressure PECVD is overwhelmingly carbon nanofibers or multi-walled carbon nanotubes because catalyst and CNTs receive severe damage from ion bombardment: single-walled carbon nanotubes (SWCNTs) has been exclusively synthesized in the thermal CVD regime except few examples. We present atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) for high-purity vertically-aligned SWCNT synthesis, because both ion-damage and radical-damage are preferentially avoided in atmospheric pressure. Tentative reaction mechanism is also discussed based gas phase chemistry analyzed by quadrupole mass spectrometer.

A rapid thermal annealing process is demonstrated for healing the defects in carbon nanotubes using a DC vacuum arc discharge system. Multi-walled carbon nanotubes (MWCNTs) grown by chemical vapor deposition at a relatively low temperature (∼650 °C) showed structural imperfections inside the tubes which are known as "bamboo-like" defects. These defects can be thermally annealed to reconstruct the graphitic structure. A vacuum arc discharge system was used to generate high temperatures (∼1800 °C) followed by rapid cooling. The MWCNTs can be rapidly annealed in such a system by several heating and cooling cycles. The annealed samples were characterized by Raman spectroscopy and transmission electron microscopy. The defects were found to be healed when the environment contained water vapor, indicating that oxygen may play an important role in breaking the imperfect graphitic structure and removing the weakly bonded defects during the rapid heating cycles. After breaking the “bamboo” segment, the graphene shell was then reconstructed during the cooling process to produce multi-shell perfection. This method produces effective defect healing and bamboo structure removal from MWCNTs.

Controlled deposition of carbon nanotubes (CNTs) across desired electrodes is important for the fabrication of nanoelectronic devices. Dieletrophoresis (DEP) has been recognized as a convenient and affordable technique for the deposition of nanotubes and nanowires on electrodes. Although DEP has been quite well studied for dielectric particles, the application for depositing nanotubes is still at the early stage of development. Here, we show that multi-walled CNTs can be deposited by DEP with controllable density and degree of alignment.

We report on a class of hybrid sensors involving single-walled carbon nanotube field effect transistors (SWNT FET's) functionalized with various oligonucleotides. These oligonucleotides include ten sequences of single stranded DNA and two sequences of single stranded. We show that the sequence of the adsorbed oligonucleotide is the key component in determining the response that the hybrid will experience upon exposure to a panel of five volatile organic compounds (VOC's). Our sensors present a change in conductance, which is specific to the analyte being tested, and the adsorbed species. Our devices respond and recover quickly (seconds), and are reproducible over ∼100 cycles. These traits are highly desirable for the creation of a technology for use as an electronic nose. We present a database of responses involving hundreds of devices.

Conventional alcohol catalytic chemical vapor deposition (ACCVD) growth of carbon nanotubes (CNTs) have been carried out under ambient gases from 103 to105 Pa. These ambient gas pressures have prevented in situ observations using an electron beam during CNT growth, such as scanning electron microscopy (SEM), scanning tunneling microscopy (STM). Therefore, in order to realize the in situ observations and to clarify the growth mechanism of nanotube, CNT growth in a high vacuum is essential. In addition, the effects of residual gases also may be avoided in the growth under high vacuum. In this study, we carried out CNT growth under high vacuum using an alcohol gas source in an ultrahigh vacuum (UHV) chamber and we achieved CNT growth below 400°C without any excitation processes of carbon source. After deposition of Co catalyst of 1 nm in thickness on SiO2/Si substrate, ethanol gas was supplied to the substrate surface through a stainless steel nozzle in the UHV chamber. The growth temperature was monitored by a pyrometer during the growth, and set between 350 and 900°C. The supply of ethanol gas was controlled by monitoring an ambient pressure, which was varied from 1 ∼10-1 to 1 ∼10-4 Pa. The grown CNTs were characterized by SEM and Raman spectroscopy. The G/Si intensity ratio reached its maximum at 700°C, when the pressure was 1 ∼10-1 Pa. The maximum point of the G/Si peak intensity shifted to a lower temperature as the growth pressure decreased. When the pressure was 1 ∼10-4 Pa, the G/Si intensity ratio reached its maximum at 400°C, at which clear RBM peaks were observed in the Raman spectrum. From the RBM peaks, the CNT diameters were estimated to be between 0.9 to 1.7 nm, and CNTs of 1.2-1.4 nm in diameter were dominant at 1 ∼10-1 Pa, whereas thinner CNTs (diameter is below 1.0 nm) were increased with the reduction of the pressure. Our largest G/D ratio was about 40 for the sample grown at 1 ∼10-1 Pa, which is considerably larger than the reported value for the CNTs grown under low pressure. From these results, we conclude that the reduction of the growth pressure lowers the growth temperature. This technique can be applied to in situ observation, and may also be useful for low temperature growth of CNTs, which opens new possibilities for the fabrication of CNT based nanodevices.

Carbon nanotube field-effect transistors (CNTFETs) were fabricated with metal material (gold) and semiconductor material (bismuth telluride) as the source and drain materials. Highly-purified HiPCO-grown single-walled carbon nanotubes (CNTs) from Carbon Nanotechnologies, Inc. (CNI) were used for the fabrication of CNTFETs. The single-walled carbon nanotubes were ultrasonically dispersed in toluene and dimethylformamide (DMF) with trifluoroacetic acid (TFA), as co-solvent. Dielectrophoresis (DEP) method was used to deposit, align, and assemble carbon nanotubes (CNTs) to bridge the gap between the source and drain of CNTFETs to form the channel. The structure of CNTFET is similar to a conventional field-effect transistor with substrate acting as a back-side gate. Electron-beam evaporation was used to deposit gold and bismuth telluride thin films. Microfabrication techniques such as photolithography, e-beam lithography, and lift-off process were used to define and fabricate the source, drain, and gate of CNTFETs. The gap between the source and drain varied from 800 nm to 3 µm. The drain-source current (IDS) of the fabricated CNTFETs versus the drain-source voltage (VDS) and the gate voltage (VG) was characterized. It was found that in the case of gold (Au) electrodes, the IV curves of CNTFETs clearly show behavior of the CNT (metallic or semiconducting) aligned across the source and drain of CNTFETs, while in the case of bismuth telluride (Bi2Te3) electrodes, the I-V curves are less dependent on the type of CNTs (metallic or semiconducting). The developed carbon nanotube field-effect transistors (CNTFETs) can be a good candidate for the application of nanoelectronics and integrated circuits with a high mobility and fast switching.

We have studied the mechanical properties of suspended graphene membranes using molecular dynamics (MD) and generalized continuum elasticity theory (GE) in order to develop and assess a continuum description for graphene. The MD simulations are based on a valence force field model which is used to determine the deformation and the elastic energy of the membrane (EMD) as a function of external forces. For the continuum description, we use the expression Econt = Estretching + Ebending for the elastic energy functional. The elastic parameters (tensile rigidity and Poisson ratio) entering Econt are determined by requiring that Econt = EMD for a set of deformations.

Comparisons with the MD results show excellent agreement. We find that the elastic energy of a supported graphene sheets is typically dominated by the nonlinear stretching terms whereas a linear description is valid only for very small deflections. This implies that in some applications, i.e. NEMS, a linear description is of limited applicability.

Closed packed film of single-walled carbon nanotubes (SWCNTs) with nanometer thickness was fabricated using a liquid-liquid interface. SWCNT was solubilized into water using sodium dodecyl sulfate as a surfactant. The SWCNTs in SDS-water suspension were used as a water phase and n-hexane was added to the suspension to form a liquid-liquid interface. After addition of ethanol to the mix solution, SWCNTs were assembled at the interface. The film form at the interface was transferred onto a silicon substrate. The AFM image of the transferred film shows a closed packed SWCNT film with a few nanometers thicknesses.

This paper reports on a real-time monitoring method for the assembly of a small number of metallic carbon nanotubes (CNTs) by dielectrophoresis (DEP). A time-varying impedance model of the electrode gap was developed to evaluate the number of CNTs which span the gap by measuring the simultaneous variation of gap impedance during the DEP process. Sudden decreases of gap impedance signals were detected during the DEP assembly of multi-walled carbon nanotubes (MWNTs) corresponding to assembly of single or multiple tubes across the gap. The method reduces the requirement of scanning electron microscopy (SEM) inspection and could help automate DEP assembly of CNTs.

Strain induced self-rolling semiconductor micro and nanotubes and related structures represent a new class of building blocks of nanotechnology. They are formed when strained planar bilayers are released from the substrate by selectively removing the sacrificial layer. Compared to other nanotechnology building blocks, one of the main advantages is the precise positioning capability due to top down fabrication approach. In this article, we demonstrate the fabrication of perfectly aligned arrays of InGaAs/GaAs nanotubes and the dispersion of freestanding semiconductor nanotubes into solution and onto foreign substrates. In addition, we systematically investigate the crystal orientation dependence of the rolling direction by using a wheel configuration. Other aspects of formation process are also discussed.

Multi-walled carbon nanotube (MWCNT) grafting onto electrospun poly(acrylonitrile) (PAN) nanofibers yields a layer by layer deposition of self assembled (LBL-SA) nanotube filaments or nanowires. PAN fibers were first functionalized with carboxylic groups through a sodium hydroxide treatment. Then, poly(diallyldimethylammonium chloride) (PDDAC), a positively charged polyelectrolyte was adsorbed onto the fibers via electrostatic interaction. When placed in contact with the modified fibers, acid treated MWCNT (ac-MWCNT) self-assemble, producing a dense and continuous layer onto the polymer nanofibers, while the inherent structure and morphology of the polymer nanofibers are retained. This method is being investigated as a universal approach applicable to a variety of materials. By producing layers of nanotubes, the electrical conductivity of polymers may be improved due to formation of a continuous MWCNT monolayer on the surface as opposed to traditional incorporation of large amounts of nanotubes into the bulk of the polymer. This method can further be implemented on polymer systems that promote a positively charged surface for COOH functionalized MWCNT to attach. Polyamides offer a perfect scenario in which they do not need to be modified to allow hydrogen bonding between the polymer and the ac-MWCNTs. Electrospun polyamide 11 (PA 11) provides a network of 100 nm and greater, fibers for deposition of ac-MWCNTs. These MWCNT coated nanofibers possess high electrical conductivity, about 0.1 S/cm, resulting from a dense coverage of MWCNTs on the polymer surface.

In an effort to increase the internal and external diameter of the RNT's, tricyclic GΛC base derivatives (XGΛC) have been synthesized and characterized. Hierchichal self-assembly results in formation of RNT's with an increased diameter, as evidenced by AFM and TEM measurements. Progress on the derivitization and characterization of the XGΛC RNT's will be presented.

Recently there has been an increase in the use of composite materials for aircraft construction. Composites have significant production and application advantages, but generally suffer from being electrically insulating, and hence are unable to handle a lightening strike in the traditional way that aluminium would. A potential solution to this problem is sought through the use of carbon nanotubes and carbon nanographite. Achieving the correct dispersion of the conducting filler is critical to achieving the desired enhancement in conductivity. Two different methods have been explored to achieve the dispersions; – direct blending and solution dispersion, with a range of concentrations of nanographite being incorporated. In addition, the effect of directly blending graphite nanoplatelets and carbon nanotubes in order to create a hybrid nanocomposite material was studied. The carbon nanotubes were incorporated into a blend with the graphite nanoplatelets with the intention of utilizing their tube structure in order to bridge the gaps between the platelet sheets of nanographite, creating more effective and abundant conductive pathways throughout the composite. In all cases the electrical conductivity was measured using a four point probe technique.