Electrical treeing (ET) is a stepwise dielectric breakdown process that generates a branched, hollow network of tubules in the dielectric between the electrode and ground. In this study, the controlled growth of electrical trees (ETs) in epoxies is demonstrated as a technique for fabricating synthetic vascular systems in engineering materials. A number of experimental conditions are explored, including AC versus DC voltage and geometric arrangement of the electrode and ground. AC growth tends to induce highly branched, “bush-like” trees while DC growth tends to produce lower-order branched structures. In addition, treating electrode surfaces with multi-walled carbon nanotubes (MWCNTs) is shown to promote ET initiation, most likely due to enhancements in the local electric field intensity. The utility of these structures for vascular applications is demonstrated by filling the channels with dyed liquids.

Discrete current switching is induced in carbon nanotubes by electron beam irradiation. Switching amplitudes of 3% to 6% are observed at room temperature. Switching is created by electron beam exposure with dosage as low as 1000 pC/cm. Relative switching amplitude remains constant as the bias voltage varies, suggesting that current fluctuation is dominated by mobility fluctuation. Changes in the noise power spectral density following electron beam exposure will be discussed.

The structure and vibrational spectrum of Gd2 and Gd2C2 endofullerenes are studied through Raman spectroscopy and universal force field (UFF) calculations. Hindered rotations, shown by both theory and experiment, indicate the formation of a Gd–cage bond, which reduces the ideal symmetry of the cage. We have conducted Raman studies of Gd2@C90, Gd2@C79N, and Gd2C2@C92. We have also studied Y2C2@C92 for comparison. Several modes have been identified which provide information about the endohedral complex.

The unique properties of carbon nanotubes (CNTs) strongly depend on their structures. In this study, the growth kinetics of ultra-long multi-walled CNT (MWCNT) arrays by water-assisted chemical vapor deposition (WACVD) has been investigated based on the statistical studies of CNT wall number. It was found that the kinetics of MWCNT arrays in WACVD demonstrated a lengthening and thickening growth. In the linear lengthening stage, CNT wall number remains constant and catalysts preserve the activity; while in the thickening stage, CNTs thicken substantially through the gas phase-induced thickening process and catalysts start to deactivate. The effects of ethylene and hydrogen flow rates on the MWCNT array growth have also been studied. It was found that by changing ethylene flow rate, different linear lengthening stages corresponding to different CNT wall numbers could be obtained. These findings provide experimental solutions to fabrication MWCNT arrays with both selective heights and controllable wall numbers by WACVD.

Vertically-aligned multiwalled carbon nanotubes (VA-MWCNTs) were grown using plasma enhanced chemical vapor deposition (PECVD) technique. These VA-MWCNTs were then dip coated by Poly methyl methacrylate (PMMA) followed by annealing. Samples were then polished to expose the tips of CNTs. Biological molecules Glucose Oxidase (GOx) were then immobilized on the exposed tips of these nanoelectrode ensembles. Here we present further characterization of these devices, with results on the detection limits and measurement stability. We found that these sensors can be reused for longer than eight months when kept in proper storage conditions.

The work function is one of the crucial quantities in understanding their field emission properties and applying carbon nanotubes to electronic devices. We perform the systematic study of work functions of 44 kinds of isolated single-walled carbon nanotubes in the framework of the density functional theory. It has been revealed that the first-principles study plays a very important role for predicting various properties of carbon nanotubes. In general, we have to perform the structural relaxation in order to know the accurate electronic properties of carbon nanotubes. Therefore we carry out the complete geometrical relaxations for 44 kinds of carbon nanotubes and evaluate their work functions. The diameters (D) of nanotubes studied satisfy 0.3 < D < 2.0 nm. Especially, we focus on the small diameter carbon nanotubes. We determine the values of work functions from the difference between the Fermi level and the vacuum level. In the semiconducting carbon nanotubes, the Fermi level is chosen at the midgap. As a result, it is found that the carbon nanotubes should be classified into three classes according to the diameter and chiral-angle dependences of work functions.

Single-walled carbon nanotubes (SWCNTs) prepared by the HiPco process were purified using a modified gas phase purification technique. A TEM-STM holder was used to study the morphological changes of SWCNT ropes as a function of applied voltage. Kink formation, buckling behavior, tubular transformation and eventual breakdown of the system were observed. The tubular formation was attributed to a transformation from SWCNT ropes to multi-walled carbon nanotube (MWCNT) structures. It is likely mediated by the patching and tearing mechanism which is promoted primarily by the mobile vacancies generated due to current-induced heating and, to some extent, by electron irradiation.

The structural and electronic properties of graphene nanoribbons (GNRs) modified by H, CO, and NH3 molecules at their edges under uniaxial strain is investigated by means of first principles calculations. It is found the bond length of the reconstructed edge of a H-terminated GNR modified by CO is larger than those of a bare GNR, a H-terminated GNR, and a H-terminated GNR modified by NH3. It is also found the band gaps of a H-terminated GNR and a H-terminated GNR modified by CO are twice the gap of a bare GNR, and the band gaps of a bare GNR and a H-terminated GNR increase with the increase of imposed strain.

The influence of hydrogen on the growth of carbon nanostructures in thermal chemical vapor deposition is studied using density functional theory calculations. It is shown that hydrogen adatoms effectively bind to edges of graphitic structures on the Ni (111) surface. This is found to result in a significant decrease of the rate of carbon attachment to the growing graphitic structures. However, it is also demonstrated that the edges of graphitic structures which are attached to steps on the Ni surface should not be hydrogenated.

The application of transparent single-walled carbon nanotube (SWCNT) electrodes in rigid and flexible alternating current electroluminescence (ACEL) devices is demonstrated. SWCNT thin film electrodes (50 – 160 nm) were made using a spray-coating process suitable for adjusting transparency and sheet resistance. The emission intensity was as high as for indium tin oxide (ITO) based ACEL devices with transparencies comparable to ITO coated polymer slides.

Glassy polymeric carbon (GPC) is a material commonly used for making electrodes for cyclic voltammetric (CV) and amperometric measurements. Previous work done at Alabama A&M University (AAMU) has shown that high energy ion beams can be used to improve the physical properties of GPC in general. In this work, we fabricated a glassy polymeric carbon electrode and we used carbon ions to activate it. Surface analyses including Raman spectroscopy, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were performed to compare the changes in surface morphology and structure before and after carbon ion bombardment.

The paper describes the fabrication and characterization of an ionic junction nanodevice as a biosensor using surfactant coated single walled carbon nanotubes (SWCNT's) via microcontact printing and its application in detecting standard protein biomolecules ( biotin-avidin). Intrinsic semiconducting SWCNT's are doped with anionic and cationic surfactant molecules respectively. Using double patterning process, these ionically doped anionic and cationic semiconducting SWCNT's are alternatively symmetrically patterned in a parallel array to form crossbar junctions onto base microelectrode arrays using flexible polymeric poly-dimethylsiloxane (PDMS) stamps. Parallel alignment of SWCNT's is achieved, due to transfer of the inked SWCNT's from the PDMS relief structure onto the microelectrode array. Base microcontacts on the microelectrode array serve as a platform for measuring electrical characteristics that get modulated due to the biomolecule binding. Functionality of the nanodevice is demonstrated by measuring impedance changes due to biomolecule binding. The modulation of the electrical behavior indicates the existence of potential for using ionically doped nanomaterial systems in fabricating functional building blocks for biosensors.

Purified carbon nanotubes (with removed toxic catalytic particles) have been considered as novel materials for drug delivery and for generating artificial organs more efficiently than traditional tissue engineering materials due to their unique surface features. The surface chemistry of carbon nanotubes has been modified through various functionalization strategies to increase biocompatibility. Importantly, modulating the intrinsic material surface energy of carbon nanotubes (without functionalization, thus, establishing permanent, non degradable chemical, and physical surface properties) can potentially reduce an immune response mediated by macrophages. Herein, we report macrophage responses on different surface energy carbon nanotubes while keeping their nanoscale surface roughness. Specifically, interactions of ultra hydrophobic (bare or unmodified) and hydrophilic carbon nanotubes (due to the formation of oxide layers) with macrophages were investigated. It was observed that macrophage density on both carbon nanotube scaffolds were lower than on traditional materials. In particular, the amount of released cytokine (TNF-α) from macrophages cultured on hydrophilic carbon nanotube scaffolds was much smaller than on hydrophobic carbon nanotube scaffolds. All results clearly supported that tailoring the surface energy of carbon nanotubes mediates a macrophage immune response.

Two molecular modes of amphiphilic block copolymer-carbon nanotube interactions have been suggested in the literature, involving the adsorption of either individual block copolymer molecules or of multimolecular, spherical block copolymer micelles on the carbon nanotube. In both cases, the nature of stability imparted to the dispersion of nanotubes is kinetic, controlled by the steric barrier imposed by the adsorbed individual molecules or micelles. In this study we propose an alternate mode of molecular interaction, wherein the block copolymer molecules self-assemble around the nanotube to generate a thermodynamically stable aqueous dispersion. The possibility of such micellar solubilization of nanotubes is examined by constructing a phenomenological theory of nanotube solubilization. Illustrative calculations performed for polyethylene oxide- polypropylene oxide – polyethylene oxide (PEO-PPO-PEO) triblock copolymers show that they are capable of solubilizing carbon nanotubes in aqueous solutions. While the block copolymer molecules that spontaneously form cylindrical micelles are most likely to solubilize the nanotubes, other copolymers whose natural curvature is spherical or lamellar also are capable of forming cylindrical micelles around the nanotubes. Most interestingly, the solubilization is found to be size specific suggesting that this can be developed into a practical method to fractionate carbon nanotubes by size or chirality.

Aluminum oxide (Al2Ox) buffer layers were employed to grow single-walled carbon nanotubes (SWNTs) at 400°C using an alcohol gas source and a Co catalyst. By optimizing the thickness of the aluminum oxide layer, the SWNT yield was enhanced by a factor of several times. In addition, SWNT growth at 350°C was realized on the Al2Ox buffer layer by this method. Raman measurements at various excitation wavelengths suggest that a Al2Ox buffer layer preferentially enhances the growth of SWNTs with larger diameters (>1 nm).

We study pressure-induced structural phase transition of carbon nanotubes using the constant-pressure tight-binding molecular-dynamics simulation. The systems studied are nanotube bundles composed of (6,6) armchair nanotube and/or (7,4) chiral nanotube, which are reported to be the nanotubes relatively abundant in experimentally purified sample. We find that the nanotube bundles transforms into a new phase that consist of graphitic ribbons and diamond blocks, “graphitic nanoribbon solid”. It is also found that sp3-rich phases obtained from the armchair nanotubes possess an anisotropic network and have high hardness which is comparable to that of cubic diamond. In the case of the bundles containing chiral nanotubes, on the other hand, amorphous diamond phase is obtained. Based on the local-density approximation in the density-functional theory, we also investigate the energetics and electronic structure of some of new carbon phases obtained in the molecular-dynamics study.

We propose a wavelength-dependent figure of merit for transparent conducting nanotube networks, composed of the sheet resistance and the optical density. We argue that this would be more useful than previous suggestions, because it relies on more realistic assumptions regarding the optical parameters of real nanotubes.

Carbon nanotubes with their attractive properties, one-dimensional character, and their large aspect ratio are ideal candidates for a variety of applications including energy storage, sensing, nanoelectronics, among others. We have studied the growth of carbon nanotubes on copper substrates using a nickel thin film as a catalyst. The catalyst was sputtered in a chamber having a base pressure in the ultra-high-vacuum regime. By adjusting the sputtering parameters, the effects of the morphology and the thickness of the nickel catalyst on the growth of carbon nanotubes have also been investigated. Multiple hydrocarbon sources as carbon feedstock (methane, acetylene and xylene) and corresponding catalyst precursors and varying temperature conditions were used during the Chemical Vapor Deposition (CVD) process to understand and best determine the ideal conditions for carbon nanotube growth on copper. Correlation between the thickness of the thin film nickel catalyst and the carbon nanotube diameter is also presented in the study. Characterization techniques used to study the morphology of the CNTs grown on copper include SEM, TEM and HRTEM, Raman Spectroscopy

The evolution of carbon onion structure from spherical to polyhedral is correlated with changes in the sp3/sp2 ratio as a function of increasing synthesis temperature using electron energy loss spectroscopy, scanning electron microscopy, and high resolution electron microscopy. Results that are obtained using asymmetric f-variance versus symmetric Gaussian deconvolution of electron energy loss spectra are compared. The possibility of a separate peak at 287 eV is discussed.

Composite film of carbon nanotube (CNT) and polytetrafluoroethylene (PTFE) was formed with despersion fluid of CNT and PTFE. The film showed high electrical conductivity in the range of 5-13S/cm. This conductive film was applied on the stainless steel bipolar plate for the polymer electrolyte membrane fuel cell (PEMFC) as anticorrosion film. This coating decreased the contact resistance between the surface of bipolar plate and the membrane electrode assembly (MEA) of the PEMFC. Therefore, the output power of the fuel cell was increased by 1.6 times.