Well-ordered aligned arrays of multiwalled carbon nanotubes were synthesized by the catalytic thermal chemical vapor deposition (CVD) in acetylene gas at the atmospheric pressure. Abrupt spark–type light emission spots and release of the carbon nanotubes from the cathode and succeeding deposition onto the anode without decomposition has been detected above the threshold electron emission current. Spectral analysis of the light showed that the spectra consist of a background similar to blackbody radiation and a set of sharp lines identified with the radiative transitions of excited carbon and iron atoms. Light emission spectra were found to be essentially different depending on the type (AC or DC) of the applied bias voltage and its value. As-grown and re-deposited materials were characterized by Raman spectroscopy and scanning electron microscopy. It was found that the structural properties of the re-deposited carbon nanotubes remained intact, with only negligible amorphization. A mechanism of the spark emission and re-deposition processe is proposed and discussed in terms of fast overheating of CNT, after explosion type melting of Fe-catalyst nanoclusters, followed by CNT transfer from cathode to anode.

We have measured the bending modulus of several different CVD (chemical vapor deposition) grown MWNTs using a vibrating reed technique. The MWNTs are produced from a thermal decomposition of three different precursors: (i) xylene/ferrocene, (ii) xylene/ferrocene/melamine (nitrogen-doped), and (iii) trimethylamine (TMA)/ferrocene. The first two precursors are used to compare the mechanical properties of typical CVD-grown to bamboo-type MWNTs. Nanotubes prepared using the third precursor shows relatively fewer walls (∼ 4–20 compared to ∼15–40)) and defects compared to those prepared from the xylene/ferrocene mixture. The resonant frequencies of these nanotubes were measured optically in air using a dark field light microscope. The diameters of these nanotubes range from 50 – 160 nm as determined from TEM and the average length is ∼ 10 microns. For the xylene/ferrocene and trimethylamine/ferrocene tubes, the average bending modulus is estimated to be 0.1 and 0.3 TPa, respectively. However, the bending modulus for the nitrogen-doped tubes is ∼9 GPa which is significantly lower compared to regular MWNTs implying that the bending modulus decreases with an increase in wall defects. These findings are in reasonable agreement with those reported previously by Wang et al.

Cup-stacked carbon nanotubes (Cup-CNTs) was fluorinated in a temperature range RT-500• •by 0.5–1 atm elemental fluorine. The F/C atomic ratio (CF0.4-CF1.2) and the color are strongly dependent on the fluorination conditions. The color of fluorinated Cup-CNTs (F-Cup-CNTs) varies from black, through gray and yellow to white. The form and morphology of the pristine tubes were well preserved after fluorination, and the fluorination results in the functionalization and modification of pristine Cup-CNTs with respect to electrochemical properties. The F-Cup-CNTs as cathodes for primary Li cells discharge satisfactorily with 100% cathode utility.

Single wall carbon nanotubes (SWNTs) have drawn considerable attention from the scientific community based on their potentially unique 1-D electronic and optical properties as well as mechanical properties. These characteristics result from the one dimensional quantum wire structure of CNTs, which have the spike-like van Hove singularities (vHs) in the electronic density of states. The detailed shape of the density of states function depends sensitively on CNT type semiconducting (sem-) versus metallic (met-)), diameter and chirality. Using the preferential affinity of amines towards sem -SWNTs, our group has been able to attain bulk separation by type based on a differential solubility of SWNTs according to the amine organization interaction on the nanotube surface. It has been argued that stable dispersions of sem -SWNTs with surfactant-amines originate from the organization of the aliphatic chain along the nanotube sidewalls, along with a small amount of zwitterions. The separation of sem-enriched SWNTs assisted by octadecylamine (ODA) had been depicted in the form of either small amount of zwitterionic interaction between carboxylic acid groups of acid-purified SWNTs or the physisorption on the SWNTs sidewall, leaving met -SWNTs in the precipitate.

Due to their exceptional thermal properties, single-wall carbon nanotubes (SWNT) are considered as very promising filler materials for improving the thermal conductivity of conventional polymers. We carefully investigated the thermal conductivity of SWNT/PMMA nanocomposites with SWNT loading in the range up to10 wt% using the comparative technique. The samples were prepared by coagulation method. We demonstrated moderate improvement in the composites’ thermal conductivity of about 250% at 10wt%. The experimental results were analyzed using the versatile Nielsen model, which takes into account many important factors, like the fillers aspect ratio and maximum packing fraction. The aspect ratio of SWNT material used to prepare our composites was determined by AFM and careful image analysis in order to use it as an input parameter in the Nielsen model. We obtained good agreement between our experimental results and the predictions of the Nielsen model. Based on our analysis we concluded that higher aspect ratio of filler material was needed to achieve better improvement in the composites thermal conductivities. One should also take steps in order to improve the thermal contact between the SWNT network and the matrix material.

Nanotube-based systems are good candidates for optical limiting against broadband laser pulses. We explore new routes to improve their limiting performances. We show that the diameter of the nanotubes is a key factor to control the performances. On the other hand, we demonstrate that chemically modified nanotubes can be mixed with organic chromophores, leading to high performance composite limiting systems which are particularly efficient in the nanosecond regime due to the cumulative effects of nonlinear scattering and multiphoton absorption.

Carbon nanotubes have shown promising properties for applications in electronic circuits and other device structures. Several device structures have been demonstrated in recent years by manual manipulation of single nanotubes. The integration of large numbers of nanotubes on wafer size substrates, however, has been a challenge.

Our approach addressing this issue utilizes nano-patterning methods in combination with plasma enhanced chemical vapor deposition to directly assemble carbon nanotubes on wafer structures. A secondary formation step is used to actually form device structures connecting the nanotubes to electrode structures. We present first results demonstrating the feasibility of our approach. Electrode structures were prepared using multi-step electron beam lithography processes. Carbon nanotubes were grown in pre-defined locations, and contact formation procedures were carried out to establish multi-terminal contact structures.

We use an analytical solution for bending of coaxial orthotropic cylinders to model the flexural deformation of multi-walled nanotubes with any number of layers. The simulation results show that the bending stiffness of the MWNT increases with the number of nanotube layers. For fixed number of layers, MWNT with larger inner radius has greater bending stiffness. The bending stiffness also increases with out layer radius. For certain outer radius, smaller inner radius results in a larger stiffness. The effective elastic modulus of the MWNT also increases with the number of layers and the outer radius. For the same value of the outer radius, the MWNT with smaller inner radius has a larger effective elastic modulus. As the number of layers increases, the effective modulus approaches the in-plane elastic modulus of graphene. In this work we find that the interface conditions, i.e., perfect bonding or no friction, do not affect the bending stiffness and effective elastic modulus of the MWNT. Furthermore, the cross-section of MWNT does not show any warping under bending, which suggest the classic beam theory is applicable in determining the flexural response of MWNT.

The understanding of the conformational interaction between conjugated polymers and carbon nanotubes in solution is essential to develop the applications of carbon nanotubes, particularly conjugated polymer-carbon nanotube hybrid materials. The visible absorption spectroscopic study shows that curved carbon nanotube surfaces can induce the planarization of individual conjugated polymers such as poly(p-phenyleneethynylene)s and poly(3-alkylthiophene)s in solution. The impact of nanotube surface quality on the interaction between carbon nanotubes and conjugated polymers is investigated.

We have synthesized multi-walled carbon nanotubes (MWNTs) on nickel-deposited n-type silicon substrates by thermal chemical vapor deposition (Thermal CVD). The electroless plating method was adopted in the deposition of the Ni catalytic layer. Sulfuric acid solution was used as a buffer to adjust and maintain a pH value of 4.6. Both the deposition time of the nickel catalyst layer and the growth time of MWNTs were adopted to control the length and density of MWNTs. Scanning electron microscopy (SEM) images showed that the density of carbon nanotubes increased as the deposition time of nickel catalyst layer increased. The formation of nickel nucleation becomes rich as the immersion time of the substrate in electroless plating solution was longer, and this benefited the growth of carbon nanotubes. In addition, the Raman spectrum demonstrated that the ID/IG ratio of MWNTs decreases as the deposition and growth time increase, indicating that more graphene MWNT structures were formed.

Plasma enhanced chemical vapor deposition (PECVD) is a unique technique for growing vertically-aligned multiwall carbon nanotubes (VA-MWNTs) at controllable tube densities. This technique is of considerable importance for low temperature growth of VA-MWNTs at desired locations. However, the graphitic order of these MWNTs is inferior to those grown by laser ablation, arc discharge, and thermal CVD techniques. Previously, these VA-MWNTs were grown by a one-plasma approach (DC, microwave etc), either for gas decomposition or substrate biasing. Here, we describe a dual-RF plasma enhanced CVD (dual-RF-PECVD) technique that offers unique capability for controlling the graphitic order and diameters of VA-MWNTs.

The structural and dynamical properties of C60 chains inserted inside Single Walled carbon Nanotubes (SWNT) have been investigated by x-ray and neutron diffraction, and inelastic neutron scattering (INS). The measurements have been performed on a large mass of a very high quality carbon peapods sample. We showed that powder diffraction could hardly give definitive response on the way the C60s are bonded inside SWNT. However, the comparison of the neutron-derived generalized density of states (GDOS) of the inserted C60 peas with the GDOS of the same objects derived from lattice dynamics calculations led to unambiguous results. The observation of excitations in the 8–15 meV range is a clear evidence for the presence strong bonds between C60s in the sample. In the same time, the observation of a very weak quasi-elastic signal may be related to rotational motions of C60 monomers inside the SWNT. These results suggest that peapods are made of a mixed phase of C60 monomers and C60 n-mers.

In this work, several silver-plated graphite rods have been evaporated using the dc-arc discharge technique in the presence of helium quenching gas. The evaporated materials deposited on the cathode and the chamber walls were characterized. It was found that the inner core of the deposited materials contains no encapsulated silver but unusually long bundles of carbon nanotubes. In addition, the soot removed from the walls presents evidence for encapsulated nanocrystalline silver as well as low-mass fullerene cages.

Atomic vibrations are partially screened by electrons. In a metal this screening can change rapidly for vibrations associated to certain points of the Brillouin zone, entirely determined by the shape of the Fermi surface. The consequent anomalous behaviour of the phonon dispersion is called Kohn anomaly. Graphite is a semimetal. Nanotubes can be metals or semiconductors. We demonstrate that two Kohn anomalies are present in the phonon dispersion of graphite and that their slope is proportional to the square of the electron-phonon coupling. Metallic nanotubes have much stronger anomalies than graphite, due to their reduced dimensionality. Semiconducting nanotubes have no Kohn anomalies.

Multi-walled carbon nanotube (MWNT) filled polystyrene (PS) composites were synthesized for electromagnetic interference (EMI) shielding applications. SEM images of composites showed the formation of the conducting networks through MWNTs within the PS matrix. The measured DC conductivity of composites increased with increasing MWNT loading, showing a typical percolation behavior. EMI shielding characteristics of MWNT-PS composites were investigated in the frequency range of 8.2–12.4 GHz (X-band). It was observed that the shielding effectiveness (SE) of such composite increased with the increase of MWNT loading. The SE of the composite containing 7 wt% MWNTs could reach more than 26 dB in the measured frequency region.

Single-walled carbon nanotubes (SWNTs) were synthesized both in powder form and on substrates using alcohol catalytic chemical vapor deposition method (ACCVD). A detailed parametric study was conducted. As-grown SWNTs were analyzed using transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FE-SEM) and Raman spectroscopy. Nucleation and growth of SWNTs occurred within seconds after introduction of the alcohol vapor. The results show that high quality SWNTs with a narrow diameter distribution without amorphous carbon can be grown using Co acetate catalyst doped with Fe acetate above 750°C. Defective nanotubes were observed at low (450°C) and high (950°C) temperatures with the optimum temperature being 850°C. In brief, our work has taken a step towards optimizing SWNTs growth conditions using ACCVD.

We present a new approach to engineer the band structure of carbon nanotube field-effect transistors via selected area chemical gating. By exposing the center part or the contacts of the nanotube devices to oxidizing or reducing gases, a good control over the threshold voltage and subthreshold swing has been achieved. Our experiments reveal that NO2 shifts the threshold voltage higher while NH3 shifts it lower for both center-exposed and contact-exposed devices. However, modulations to the subthreshold swing are in opposite directions for center-exposed and contact-exposed devices: NO2 lowers the subthreshold swing of the contact-exposed devices, but increases that of the center-exposed devices; In contrast, NH3 reduces the subthreshold swing of the center-exposed devices, but increases that of the contact-exposed devices. A model has been developed based on Langmuir isotherm, and the experimental results can be well explained.

The use of resonance Raman spectroscopy (RRS) to study and characterize single wall carbon nanotubes (SWNTs) is discussed, focusing on preliminary efforts for the development of the RRS to characterize defects in SWNTs. The disorder-induced D-band, disorder-induced peaks just above the first-order allowed graphite G-band, as well as the intermediate frequency modes (IFMs) appearing between the RBM and the D/G spectral region are addressed. RRS on nanographite ribbons and on a step-like defect in highly ordered pyrolytic graphite (HOPG) sheds light into the problem of characterizing specific defects in nano-related carbons.

Surface modification of carbon nanotubes with polyvinyl alcohol (PVOH) showed detection for humidity variation implying a possible application as a nanoscale humidity sensor. Wettability studies on single-wall, Y junction single wall and multiwall carbon nanotubes revealed that these nanotubes tend to become highly hydrophilic surfaces by this functionalisation. From the raman analysis it was determined that the majority of the nanotubes in our Y-junction single wall nanotubes were semiconducting in nature. The conductivity studies revealed that the Y junction nanotubes with PVOH functionalisation show large change in conductivity for varying relative humidity (RH). We propose a possible charge transport mechanism in these functionalized nanotubes.

We report the synthesis of organized colloidal semiconductor nanocrystal / carbon singlewalled nanotube hybrid nanostructures. The synthetic protocol described here avoids the need for covalent chemical modification of carbon nanotube (CNT) surfaces. Specifically, InP quantum dots (QDs) and CdSe QDs were found to strongly adsorb onto the surfaces of carbon single-walled nanotubes (SWNTs) by gentle heating in organic solvents. Transmission electron microscopy (TEM) was used to characterize the semiconductor nanocrystal (NC) / SWNT assemblies, and revealed that the surfaces of the SWNT bundles template the adsorption of the NCs from solution. Small QDs were found to randomly absorb onto SWNTs, while larger QDs self-assembled into long linear chains. The nature of binding and ordering was investigated by simply considering van der Waals (vdW) forces for both NC-SWNT and NC-NC interactions. Quantum rods (QRs) were also found to adsorb along the nanotube surfaces. These findings have important implications for the synthesis of NC / SWNT hybrid nanostructures.