We experimentally study the dark and photocurrent in metal-semiconductor-metal (MSM) photodetectors based on single-walled carbon nanotube film Schottky contacts on GaAs. We find that above ∼260°K, thermionic emission of electrons with a barrier height of ∼0.54 eV is the dominant dark current transport mechanism. Furthermore, MSM devices with CNT film electrodes exhibit a higher photocurrent-to-dark current ratio while maintaining a comparable responsivity relative to control devices. This work demonstrates that nanotube films can be integrated as Schottky electrodes in conventional semiconductor optoelectronic devices.

Vertically aligned multiwalled carbon nanotube (CNT) arrays were fabricated in anodized aluminum oxide (AAO) templates without the use of a catalyst, using xylene pyrolysis. The CNT arrays in AAO template were integrated into a resistive sensor design. The sensors were found to be highly responsive to NH3 and NO2 with steady state sensitivities of 5% and 10% for 100ppm of NH3 and NO2 respectively, at room temperature. Results were interpreted in terms of the CNTs acting as p-type semiconductors. A study was undertaken to elucidate the dependence of sensitivity on the thickness of the conducting amorphous carbon layers on top and bottom. Recovery of the MWNT gas sensor was studied for different types of desorption techniques. The thickness of the amorphous carbon layer (sheet resistance) was found to be critical in determining the sensor response.

Rosette Nanotubes (RNTs) are formed by the self-assembly of a guanine-cytosine motif (GΛC), a hybrid of the DNA bases guanine and cytosine, to give a six membered macrocycle maintained by 18 H-bonds. In theory, any moiety covalently attached to the GΛC base can be expressed on the nanotubes surface. However we anticipate that the self-assembly and stability of these functionalised RNTs will also be governed by steric effects. Herein we describe the synthesis and the self assembly of the Twin Base Lysine (TBL-K) and its monobase (MBL-K). While TBL-K self-assembles readily in water and methanol to give nanotubular structures, MBL-K does not form nanotubes. Various techniques were used to characterize the RNTs and the factors, preventing self-assembly in the case of MBL-K, were investigated.

Control over the dimensions of nanostructured materials is of critical importance for proper utilization in devices. There has been a number of systems reported that utilize amphiphilic molecules that organize themselves into nanotubes or tubules, as well as various polymers that can assemble into tubular nanoscale structures. The organization of these components into nanotubes is mainly driven by hydrophobic effects of the substituents in particular solvents, which contain polar and apolar portions. While studying a modification to a previously reported GC module that normally forms rosette nanotubes (RNTs) with diameters in the 4nm range, we discovered that a small modification led to the formation of nanotubes with diameters 10 times of that expected. These structures were studied by SEM, TEM, and AFM in an attempt to uncover the mechanism of their formation. It was determined that these chiral organic molecules first self-assemble into sheet-like structures, but due to an inherent curvature of the sheet, they roll into large nanotubules. This new type of self-assembled nanotube may have applications in host-guest chemistry and as templates for other nanoparticles and materials.

We discuss the energetics of Double walled Carbon nanotubes (DWCNT) peapods as compared to their single walled (SWNCNT) counterparts. We show that filling DWCNT with C60 fullerenes is energetically more favourable than SWNTs. Essentially two mechanisms are responsible for this phenomenon: 1] the interalyer state between the tubes which acts as repository of charge, 2] The Van der Waals interactions with the outer tubes. We discuss in some details the first effect using pseudopotential DFT, LDA first principles simulations for the two peapods C60@(15,0) and C60@(15,0)-(24,0)

This paper investigates the effectiveness of different pretreatment methods applied on M50, M35, and W4 type of tool steel substrates for direct growth of carbon nanotubes. The pretreatments explored include treatment with sand paper polishing, nitric acid (HNO3) etching, and high temperature hydrogen gas treatment. Furthermore, in order to establish a correlation between the steel surface average roughness value and the carbon nanotube growth, surface topography of steel substrates created by mechanical polishing were measured before actual growth process. Grown carbon nanostructures were shown by SEM and TEM to be multi-walled carbon nanotubes (MWCNTs) and vapor grown carbon nanofibers (VGCFs). It was found that under the same pretreatment conditions, even when the same roughness values were achieved and the same thermal chemical vapor deposition conditions were applied, grown nanostructures on different types of tool steel substrates showed dissimilarity.

To understand nanoribbons of graphene, we developed an ab initio parametrized fit to Carbon and Hydrogen chemical data, out to arbitrary neighbor interactions, including relaxations. Our computed band structure confirms the well-known three-family behavior of armchair bangaps but also predicts a similar familial behavior for conductance in nanoribbon transistors. The Boltzmann carrier transport simulations from calculated phonon spectra show, over a range of temperatures, the familial conductance behavior. Both the peak field-effect mobility and the "on" conductance increase with ribbon width, the later being proportional to the width and inversely proportional to the lattice temperature. We will also discuss phonon-limited scattering of charge carriers in graphene.

The self-assembly of six self-complimentary Guanine – Cytosine hybrid heterocycles bearing hydrophobic substituents has been studied using combinatorial approach in eight solvents under different conditions. The parameters that were varied include: the structure of the self-assembling module, its concentration, the solvent, temperature, and time of self-assembly. scanning electron microscopy (SEM) was used as a screening tool. A wide variety of interesting morphologies was found. The most interesting structures were studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), dynamic light scattering (DLS), and X-ray powder diffraction (XRD).

Large-scale production of perfect conical carbon nanostructures that are fundamentally different from the other nanocarbon materials, such as buckyballs and nanotubes, can be made using the so-called Kvaerner Carbon Black & Hydrogen Process. This involves pyrolysis of hydrocarbons using a torch plasma process. The carbon cones that occur appear in five distinctly different forms. In addition, disk-shaped particles may be produced. Here we report about the current status for the experimental research and theoretical modeling of these particles, which have properties different from the other known forms of carbon.

We have grown vertically-aligned carbon nanotubes on (100) silicon substrates by means of a plasma enhanced chemical vapor deposition method. The growth of CNTs is achieved by a mixture of hydrogen and acetylene gases in a CVD reactor and a 2-5nm thick nickel is used as the seed for the growth. Following the growth of nanotubes on the silicon substrates, they are covered by a titanium-oxide layer and then the substrate is placed back into the original chamber to expose to a hydrogen plasma. Depending on the hydrogenation step, the nickel seed layer, which is placed on the tip side of the original nanotube, is expanded. The subsequent process in the same reactor leads to the growth of carbon nanotubes in a branched manner. Scanning electron microscopy has been used to investigate the results of such tree-like nanostructures.

The intertube oscillations of double-walled carbon nanotubes (DWNTs) are investigated using molecular-dynamics (MD) simulation. The inner and outer tubes of model DWNTs have chiral indices of armchair type. The intertube oscillations are damped owing to energy dissipation. The logarithmic decrements and frequencies of the damped oscillations are calculated. The results show that the logarithmic decrement increases with increasing the tube diameter and decreases with increasing the tube length.

Rosette nanotubes (RNTs) were used as structure-directing agents for the synthesis of microporous and/or mesoporous silica nanotubes. The silica nanomaterials were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and CO2 and nitrogen physisorptions. The results show that the mode of the obtained porous systems as well as the surface areas and volume of micro- and/or mesopores depend on the nature of the pendant attached to the rosette nanotubes surface.

We report on microwave measurements of complex permittivity of single-walled carbon nanotubes (SWNTs). The SWNT samples are a mixture of semiconducting and metallic nanotubes suspended using Pluronic (F108) as a stabilizing surfactant agent. Other samples that were characterized include pluronic powder and an oriented carpet of multi-walled nanotubes (MWNT). For broadband measurements, the shielded open-circuited transmission line technique was used. Single frequency (resonant) measurements for liquid-based SWNT samples were carried out by employing two different modes in specially designed microwave dielectric resonators (DR), either with a cylindrical hole in the center of a dielectric disk or with a horizontal gap (split resonator). The first resonator can operate in either TE011 or TM011 modes (3.4 GHz and 6 GHz) and was designed for liquid or powder characterization. For pluronic suspended SWNT, real (epsilon) and imaginary parts of permittivity were found at 3.4 GHz as 3.5 and 0.72, respectively.

The growth of ZnO nanotubes and nanosquids is obtained by conventional thermal chemical vapor deposition (CVD) without the use of catalysts or templates. Characterization of these ZnO nanostructures was conducted by X-ray powder diffraction (XRD), Field-emission scanning electron microscopy (FESEM), Raman spectroscopy, and photoluminescence (PL). Results indicate that these ZnO nanostructures maintain the crystalline structures of the bulk wurtzite ZnO crystals. Our results show that rapid cooling can be used to induce the formation of ZnO nanotubes and ZnO nanosquids. The self-assembly of these novel ZnO nanostructures are guided by the theory of nucleation and the vapor-solid crystal growth mechanism.

We have performed a systematic investigation of the influence of the growth parameters on the synthesis of vertically aligned single-walled carbon nanotubes (VA-SWNTs) by the alcohol catalytic chemical vapor deposition (ACCVD) method. The growth process of the VA-SWNTs was monitored using an in situ optical absorbance technique and the effects of CVD temperature and ethanol pressure on the initial growth rate and the catalyst lifetime were investigated. We found that for a given CVD temperature, there is an optimum pressure at which the VA-SWNT film height is maximized, and this pressure increases with temperature. Below this optimum pressure the growth reaction is first-order, with the arrival of ethanol to the catalyst being the rate-limiting step. The activation energy of the growth was also determined to be approximately 1.5 eV.

The root-growth mechanism of VA-SWNTs by the alcohol CVD method was also confirmed by a two-stage growth process. Following a short growth period using normal ethanol, isotope labeled 13C ethanol was introduced to continue the growth. The location of the 13C was confirmed by resonance Raman spectroscopy, confirming the root-growth mechanism.