GaN nanostructure synthesis was done in a quartz tube furnace using ammonia and liquid Ga as precursors, and hydrogen as the carrier gas. Ni nanoparticles formed due to annealing, has been used as the catalyst layer, facilitating vapor-liquid-solid growth of the nanostructures. The growth process resulted in the formation of two types of structures, straight nanowires, and irregular growth sometimes resulting in nanospirals. Growth using uniform distribution of catalyst over the entire surface resulted in growth of straight nanowires, while growth performed on catalyst patterned surface resulted in growth of nanospirals. The diameter of the nanowires varied from 20 – 100 nm, while for spirals the cross-sectional diameters were found to be in the range of 100 nm – 1 micron, and spiral diameters in the range of several microns. Using the present growth system and gas flow set-up, it was possible to synthesize ultra-long nanowires and spirals, with overall lengths exceeding 70 microns. The regular straight nanowires were found to have a smooth circular cross-section, while the irregular wires and nanospirals were found to have a very rough surface with approximate hexagonal or triangular cross-sections. Some of the spirals changed into straight nanowires with uniform triangular cross-sections. While more investigations are required to fully establish their structures, based on preliminary characterization and past studies, we conclude that the nanowires with circular cross-sections grow along the c-direction [0001], while the spirals and consequent triangular cross-section nanowires grow along one of the non-polar directions. The formation of spirals themselves may be related to the polarization properties of GaN, similar to those predicted for ZnO nanosprings and nanoribbons.

Single wall carbon nanotubes (SWNTs) having semiconducting properties are promising as electronic materials for nano-scale devices in the future, and the electrical properties of SWNTs are of significantly fundamental and practical interests. It is well known that the field effect transistors (FETs) fabricated using semiconducting SWNTs show high performance in terms of the mobility. However, carriers in pristine SWNTs are mostly holes and, therefore, SWNTs -FETs usually show p-type properties. As for SWNTs, chemical carrier doping has been reported so far for controlling carrier concentration like graphite intercalations. Two major techniques in SWNTs are generally possible; one is endohedral doping and the other is the exohedral chemical modifications. It has been exemplified that doping with alkali metals can introduce electron carriers into SWNTs. Furthermore, the electrical transport properties of SWNTs were reported to be controlled by the endohedral insertion of organic molecules inside the SWNTs. A similar carrier doping could exohedrally be possible when the SWNTs surface is chemically modified. With such chemical modifications, the charge transfer from the substituent groups to SWNTs will be expected and this could modify the electronic states of SWNTs. We reported the FET properties of individual SWNTs exohedrally modified by Si-containing organic moieties, and demonstrated that p-type nanotubes can be converted to n-type ones. However, because of ununiformity of the surface-chemical modifications of SWNTs, the true effects of the exohedral modifications on FET properties were extremely difficult to be evaluated. In this meeting, we will present comparison of the FET properties of the exohedrally silylated SWNTs between separated individual and spread-sheet samples. For evaluating the FET properties, the chemically modified SWNTs have been dispersed on a FET substrate, and the measurements have been carried out at ambient temperature using a conventional method for a separated SWNTs and a spread-sheet SWNTs film. As a reference, the experiments were also made in the same manner on chemically non-modified CNTs. From the experimental results, it will be demonstrated that an n-type property can be enhanced by the exohedral modifications both in the case of the spread-sheet samples and in the case of the individual ones. We will discuss the effects of surface silylation on the electronic states of these SWNTs.

Mass produced multi-walled carbon nanotubes have examined their feasibility as an electrode for supercapacitors. Activation behavior of MWNTs with different diameter is quite different. In this study, the effect by diameter on KOH activation of MWNTs are confirmed.

We demonstrate a versatile class of nanoscale sensors based on single-stranded DNA (ss-DNA) as the chemical recognition site and single-walled carbon nanotube field effect transistors (swCN-FETs) as the electronic readout component. Coating swCN-FETs with ss-DNA causes a current change when exposed to gaseous analytes, whereas bare swCN-FETs show no detectable change. The responses differ in sign and magnitude depending both on the type of gaseous analyte and the sequence of DNA. Our results suggest that the conformation of ss-DNA on swCN-FET plays a role in determining the sensor response to gaseous analytes. The conformation depends not only on the base content of the oligomer, but also on the specific arrangement of the bases in the ss-DNA. We compare our results with the molecular dynamic simulations for understanding of the sensing mechanisms. SsDNA/swCN-FETs possess rapid recovery and self-regenerating ability, which could lead to realization of large arrays for sensitive electronic olfaction and disease diagnosis.

A theoretical analysis explaining non-catalytic growth of one-dimensional (1D) nanorods on a substrate is presented. The nuclei undergo cluster migration which continues until the mean free time of the adatoms is larger than surface diffusion time during several consecutive nuclei growth steps. The most probable mechanism is the migration of six adatoms into one fixed adatom. After the cluster migration, the nuclei grow in an isotropic manner, until the nucleus reaches the size limit. The 1D growth of nanorods on the nuclei begins when the reactant dose is smaller than a certain value. The growth rate of the height is greater than that of the radius. This difference in the growth rate causes the aspect ratio to increase with growth time. The presented analysis explains well the experimental results of the non-catalytic growth of nanorods.

ZnO nanorods were grown by catalyst-assisted vapor phase transport on Si(001), GaN(0001)/c-Al2O3, and bulk ZnO(0001) substrates. Morphology studies showed that ZnO nanorods grew mostly perpendicularly to the GaN substrate surface, whereas a more random directional distribution was found for nanorods on Si. Optical properties of fabricated nanorods were studied by steady-state photoluminescence and time-resolved photoluminescence. Stimulated emission was observed from ZnO nanorods on GaN substrates. Raman spectroscopy revealed biaxial strain in the nanorod samples grown on Si. Conductive atomic force microscopy was applied to study I-V spectra of individual nanorods.

Studies on the electronic structure of carbon nanotube (CNT) are of much importance because of its efficient utilization in electronic vacuum devices [1]. These CNTs have many applications such as field emission display (FED), LCD backlight units, microwave amplifiers, lighting lamps, x-ray sources and so on. One of these applications is the electron emitter for x-ray source. In order to obtain x-ray images of relatively hard instruments or components such as PCB board or machine tools, high quantity of x-ray current is generally required. In this study, we report that the current density of x-ray source can be greatly enhanced by using the CNT emitter as a cathode. In general, the emission current of CNT emitter is very sensitive to gap distance between CNT emitter and grid metal mesh. In addition, the emission current is appeared to be different with respect to the kinds of metal meshes and their sizes employed in the measurement. Extensive results of these were reported in our recent works [2]. For example, as the distance between CNT emitter and grid metal mesh was getting shorter, the current density of the triode was getting larger. Detailed parameters and corresponding results were presented and some preliminary x-ray images were obtained and discussed in this study.

The electron-phonon coupling in two-dimensional graphite (graphene sheet) and metallic single-wall carbon nanotubes (SWNTs) is analyzed. In the graphene sheet the G-band phonon mode induces oscillations of the Fermi points, while the G′-band phonon mode opens a dynamical (oscillating with the phonon frequency) band gap, and accordingly, both phonon modes exhibit Kohn anomalies. Similarly, truly metallic armchair SWNTs undergo Peierls transitions driven by the G−- and G′-band phonon modes both of which open a dynamical band gap. In addition, the dynamical band gap induces a non-linear dependence of the phonon frequencies on the doping level and gives rise to strong anharmonic effects in the graphene sheet and metallic SWNTs.

We have fabricated flexible electronic devices to test the strain-based change in resistance of a network of single-walled carbon nanotubes (SWCNTs) for use in microscale, high resolution magnetometry. To do this, we first develop a simple, reliable method to obtain catalyst nanoparticles for carbon nanotube growth through indirect, thin-film evaporation. Next we fabricate a two-terminal SWCNT device on a rigid substrate. We then transfer the device, intact, to a flexible substrate for strain testing. Herein, we report progress in growth and measurement techniques.

The basic step to optimize the properties of filler in composite is the interfacial interaction between the matrix and the filler. Irradiation, a novel technique, was used in this work to introduce a wide range of defects in Single-walled Carbon nanotubes (SWNTs) as filler prior to composite formation. The thermal stability along with phase transition behavior of an organic conducting polymer Poly(3-hexylthiophene) (P3HT) loaded with pristine and ion implanted SWNTs has been investigated using Thermogravimetry Analysis (TGA), Differential Scanning Calorimetry (DSC), and Electron Spin Resonance (ESR). Interestingly, we observed substantial improvement on the thermal stability and the phase transition behavior of the composite with pristine and irradiated fillers.

The role of the p-type chemical dopant, SbCl6, on Palladium (Pd)-contacted carbon nanotube field effect transistors (CNTFETs) is investigated using ab initio calculations. The interaction of SbCl6 with Pd leads to the chemisorption of one chlorine atom (Cl) which separates off from the rest of the molecule leaving behind a rehybridized SbCl5 molecule. This interaction increases the local workfunction by 0.08 eV. The interaction of the molecule with the carbon nanotube (CNT) itself results in the physisorption of SbCl6 onto CNT. The SbCl6 is found to degenerately dope CNT p-type and shifts the local potential by 0.29 eV. These barriers are useful for modelling of transport of Schottky barrier CNTFETs.

Properties of defected nanopeapods, in which a defected C60 cage with a C1–C59 topology is encapsulated inside a (10,10) single walled carbon nanotube, have been analyzed using density functional theory (DFT) calculations. When new CC bonds are formed between the defected C60 and the nanotube, the CC network of the nanotube is perturbed near the binding site, and has butadiene and quinonoid perturbations. Such geometrical changes could play an important role in the selective functionalizations of carbon nanotubes.

We report fabrication and modeling of self-defined gated filed-emission devices based on encapsulated vertically aligned carbon nanotubes grown on Si substrates with a PECVD method. The electrical characteristics of such devices have been theoretically modeled using an expanded Fowler-Nordheim tunneling effect. Devices fabricated here, resemble vacuum tubes where CNTs act as cathode. They show a saturation behavior for large distances between anode and cathode electrodes, making them suitable for transistor applications. The physical properties of the CNTs were investigated using SEM, evidencing the evolution of vertical CNTs with a tip-growth mechanism. The triode structure proposed in this paper uses CNT as the field-emission electrode (cathode), the surrounding Cr as the gate and a second Si substrate as the anode electrode. The emission current from the nanotube tips is significantly controlled by applying a negative voltage between CNT and the gate. The effect of the anode-cathode and gate-cathode voltages on the emission current has been experimentally observed and theoretically modeled using an expanded F-N effect.

The paper presents the results of competitive catalysis investigation of the carbon nanotube growth in situ of the partial oxidation process of methane. The competition between Ni and Fe results in suppression of Ni catalytic activity and the growth of Fe-capped carbon nanotubes. The discrimination is so strong that iron is segregated from Ni-Fe based stainless steel alloy leaving characteristic Ni-enriched corrosion caverns. The process strongly depends on temperature. Depending on particular catalyst bed composition, the nanotubes of various morphology may occur. In particular, the use of perovskite-type catalyst leads to formation of “olive-branch”-like peculiar carbon nanostructures.

We succeeded in growing carbon nanotubes in a photoelectron spectroscopy analysis system using thermal chemical vapor deposition and analyzed the chemical states of the Co catalysts by in-situ x-ray photoelectron spectroscopy before and after the growth. We found that almost all of the Co particles are metallic after the growth in both cases; Co particles are formed from a Co oxide thin film and a metallic Co thin film. This shows that the metallic state is stable for Co under low-pressure ethanol ambient in our growth condition for carbon nanotubes.

Carbon nanotube Langmuir-Blodgett film was fabricated using polyion complex method. Multi-walled carbon nanotube (MWCNT) synthesized by template method form a stable polyion complex monolayer at the air/water interface. The monolayer can be transferred onto a solid substrate. The AFM image of the monolayer shows a one-dimensional network structure of MWCNT..

Conditions for the transfer printing of patterned carbon nanotube (CNT) films, along with a Au-gate, a poly methylmethacrylate (PMMA) dielectric layer and Au source-drain electrodes have been developed for the fabrication of thin-film transistors on a polyethylene terephthalate (PET) substrate. Chemical vapor deposition (CVD) grown CNTs were patterned using a photolithographic method.

Transfer printing was used to fabricate devices having both top gate and bottom gate configurations. Replacement of the SiO2 dielectric with PMMA correlates with a decreased hysteresis in the transconductance behavior. Encapsulation of the CNTs between the polymeric substrate and dielectric layer yields ambipolar behavior. Variations in device performance are also observed as a function of CNT film density and channel length, suggesting changing contributions of the metallic and semiconducting CNTs to the transport mechanism.

Transmission electron microscopy (TEM) is a key technique in the structural characterization of carbon nanotubes. For device applications, carbon nanotubes are typically grown by chemical vapor deposition (CVD) on silicon substrates. However, TEM requires very thin samples, which are electron transparent. Therefore, for TEM analysis, CVD grown nanotubes are typically deposited on commercial TEM grids by post-processing. This procedure has two problems: It can damage the nanotubes, and it does not work reliably if the nanotube density is too low. The ability to do TEM directly on as-grown nanotubes lying on the silicon substrate would solve these two problems. In this work, for this purpose, we have fabricated micromachined TEM grids from silicon substrates. In particular, we have wet-etched large membranes from the back side of silicon wafers with a thin layer of thermal oxide on them. We have then etched a large array of long and narrow open slits on these membranes from the top side using a deep silicon etcher. Subsequently, we have grown nanotubes on these micromachined TEM grids by CVD, and characterized the nanotubes by high resolution TEM (HRTEM), micro-Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Since the nanotubes grown on the micromachined substrates are completely suspended over the width of the open slits, these substrates form a natural TEM grid for direct imaging of CVD-grown nanotubes. Furthermore, the signal from the substrate is significantly reduced during micro-Raman spectroscopy, resulting in a better signal-to-noise ratio. In addition, the silicon membranes are strong enough to support AFM and SEM characterization. As a result, these substrates provide a low cost, mass producible, efficient, and reliable platform for direct TEM, Raman, AFM, and SEM analysis of as-grown nanotubes or other nanomaterials on the same substrate, eliminating the need for any post-processing after CVD growth.

Carbon nanotubes (CNT) have been studied intensively for explorations of their unique electrical and mechanic properties in many applications. However, direct and functional integration of carbon nanotubes with silicon to form an electronically functional structure or device has remained a great challenge. Whereas vertically aligned bundles of nanotubes have been grown previously on silicon, the integration is mechanical, rather than electronical, in nature and the application of such mechanical integration is rather limited. In this work, we report on electronically functional integration of carbon nanotube with silicon, i.e., the formation of an electronic heterojunction by controlled growth of vertical and highly ordered array of ‘carbon nanotube - silicon’ (CNTS) heterojunctions of uniform diameter, length, and alignment. Moreover, we examine it as a hyperspectral photodiode. From the measured spectral dependence of the photocurrent, one may also extract the band gap of the nanotubes, which we find to be in agreement with that determined from conductance measurements. Mechanism of the infrared photocurrent response is elucidated by the current-voltage (I-V) and radiation intensity-photoresponse measurements. The linear intensity dependence of the photoresponse in the absorption ranges of Silicon and CNTs and the measured I-V characteristics all suggest that the photocurrent responses corresponding to the Silicon and CNT bands both originate from the intrinsic functionality of the heterojunction.

The large surface to volume ratio in nanometer sized wire structures cause a strong dependence of the optical Raman mode on the thermal conductivity of a surrounding medium. On the basis of optical measurements on silicon nanowires as a function of excitation laser power we explain the very large red-shifted Raman spectra observed already for moderate laser powers. This thermal effect is enhanced by a silicon oxide sheath, rendering a reduced thermal contact of the wires to the substrate. The intrinsic redshift due to spatial confinement in silicon nanowires is found to be smaller than 2 cm−1.