Superhydrophobic carbon nanotube/silicon carbide nanowire nanocomposites

The composite film of carbon nanotubes and silicon carbide nanowires was synthesized directly on the silicon substrate by the catalyst-assisted method. The carbon nanotubes crimped together decorated with silicon carbide nanowires covering the whole substrate. The appropriate amount of aluminum powders is a crucial factor to achieve the composite film. The composite film exhibited excellent intrinsic superhydrophobicity without any further functionalization. By using the nano/micropillar composite structure model, the presence of silicon carbide nanowires is found to be the key factor that results in the superhydrophobicity of the films. The feasible synthesis of the superhydrophobic coating could have potential application in water-repelling devices, like biochemical sensors and microfluidic systems.     

Observation of breathing-like modes in an individual multiwalled carbon nanotube

We study collective vibrational breathing modes in the Raman spectrum of a multiwalled carbon nanotube. In correlation with high-resolution transmission electron microscopy, we find that these modes have energies differing by more than 23% from the radial breathing modes of the corresponding single-walled nanotubes. This shift in energy is explained with intershell interactions using a model of coupled harmonic oscillators. The strength of this interaction is related to the coupling strength expected for few-layer graphene.     

Linear nanomotor based on electromigration of a nanoparticle encapsulated in a carbon nanotube

We investigated a linear nanomotor based on the telescoping carbon nanotube motion induced by electromigration of an encapsulated nanoparticle. The nanoparticle motion induced by the electric current makes the inner nanotube linearly telescope or retreat. Theoretical results using a kinetic Monte Carlo method were in good agreement with previous experiments. The telescoping speed of the linear nanomotor exponentially decreased with increasing mass of the inner nanotube.     

Sensitivity of a superconducting nanowire detector for single ions at low energy

We report on the characterization of a superconducting nanowire detector for ions at low kinetic energies. We measure the absolute single-particle detection efficiency η and trace its increase with energy up to η = 100%. We discuss the influence of noble gas adsorbates on the cryogenic surface and analyze their relevance for the detection of slow massive particles. We apply a recent model for the hot-spot formation to the incidence of atomic ions at energies between 0.2 and 1 keV. We suggest how the differences observed for photons and atoms or molecules can be related to the surface condition of the detector and we propose that the restoration of proper surface conditions may open a new avenue for SSPD-based optical spectroscopy on molecules and nanoparticles.     

Charge noise in liquid-gated single-wall carbon nanotube transistors

The noise properties of single-walled carbon nanotube transistors (SWNT-FETs) are essential for the performance of electronic circuits and sensors. Here, we investigate the mechanism responsible for the low-frequency noise in liquid-gated SWNT-FETs and its scaling with the length of the nanotube channel down to the nanometer scale. We show that the gate dependence of the noise amplitude provides strong evidence for a recently proposed charge-noise model. We find that the power of the charge noise scales as the inverse of the channel length of the SWNT-FET. Our measurements also show that surprisingly the ionic strength of the surrounding electrolyte has a minimal effect on the noise magnitude in SWNT-FETs.     

Evaluation of a pyroelectric detector with a carbon multiwalled nanotube black coating in the infrared

The performance of a pyroelectric detector with a carbon multiwalled nanotube coating was evaluated in the 0.9-14 microm wavelength range. The relative spectral responsivity of this detector was shown to be flat over most of the wavelength range examined, and the spectral flatness was shown to be comparable to the best infrared black coatings currently available. This finding is promising because black coatings with spectrally flat absorbance profiles are usually associated with the highest absorbance values. The performance of the detector (in terms of noise equivalent power and specific detectivity) was limited by the very thick (250 microm thick) LiNbO3 pyroelectric crystal onto which the coating was deposited. The responsivity of this detector was shown to be linear in the 0.06-2.8 mW radiant power range, and its spatial uniformity was comparable to that of other pyroelectric detectors that use different types of black coating. The carbon nanotube coatings were reported to be much more durable than other infrared black coatings, such as metal blacks, that are commonly used to coat thermal detectors in the infrared. This, in combination with their excellent spectral flatness, suggests that carbon nanotube coatings appear extremely promising for thermal detection applications in the infrared.     

Electrical properties of multiwalled carbon nanotube reinforced fused silica composites

Multiwalled carbon nanotube (MWCNT)-fused silica composite powders were synthesized by solgel method and dense bulk composites were successfully fabricated via hot-pressing. This composite was characterized by XRD, HRTEM, and FESEM. MWCNTs in the hot-pressed composites are in their integrity observed by HRTEM. The electrical properties of MWCNT-fused silica composites were measured and analyzed. The electrical resistivity was found to decrease with the increase in the amount of the MWCNT loading in the composite. When the volume percentage of the MWCNTs increased to 5 vol%, the electrical resistivity of the composite is 24.99 omega cm, which is a decrease of twelve orders of value over that of pure fused silica matrix. The electrical resistivity further decreases to 1.742 omega. cm as the concentration of the MWCNTs increased to 10 vol%. The dielectric properties of the composites were also measured at the frequency ranging from 12.4 to 17.8 GHz (Ku band) at room temperature. The experimental results reveal that the dielectric properties are extremely sensitive to the volume percentage of the MWCNTs, and the permittivities, especially the imaginary permittivities, increase dramatically with the increase in the concentration of the MWCNTs. The improvement of dielectric properties in high frequency region mainly originates from the greatly increasing electrical properties of the composite.     

Charge imbalance in superconducting tin films produced by a supercurrent in the presence of a temperature gradient

A pair-quasiparticle potential difference V arising from a quasiparticle charge imbalance has been measured in superconducting tin and tin-indium films along which there exist both a supercurrent I and a temperature gradient T. The voltage is proportional to I T at a given temperature, and near T _cdiverges approximately as (1 \s- t)^\s-1 for given values of I and T. Theories by Schmid and Schön and by Clarke and Tinkham are in good agreement with the temperature dependence and magnitude of V/(I T), while a theory by Beyer Nielsen et al. predicts the correct magnitude but a temperature dependence of (1 \s- t)^\s-1/2.This work was supported by the Phillips Foundation of 1958, the Danish Natural Science Research Council, and the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Science Division, U.S. Department of Energy under contract No. W-7405-ENG-48.     

Synthesis and characterization of multiwalled carbon nanotube/FeCo nanocomposites

Multiwalled carbon nanotube/FeCo nanocomposites were produced by Catalytic Chemical Vapour Deposition using highly porous FeCo-SiO2 aerogels with different loadings and dimensions of FeCo nanoparticles as catalysts. Multiwalled carbon nanotubes with average number of walls depending on the size of the catalyst nanoparticles were obtained. Inside the nanotubes spherical or elliptical FeCo nanoparticles are retained, and the magnetic properties of the resulting nanocomposites were characterized in detail.     

Temperature effects on resistance of aligned multiwalled carbon nanotube films

Electrical transport in vertically aligned films of multiwalled carbon nanotubes has been investigated in the -150 degrees C to 300 degrees C temperature range (all the tests were conducted in air at atmospheric pressure). In all the cases, the nanotube film exhibited a semi-conducting behavior, with the film resistance decreasing with increasing temperature. Removal of amorphous carbon contamination (via plasma etching) significantly improved the nanotube film's sensitivity to temperature changes (particularly in the 20 degrees C to 200 degrees C temperature range). All the of films tested in this study showed a consistent, repeatable behavior that was independent of the nanotube film length. The temperature sensitivity of the nanotube films was also found to be independent of the heating/cooling rates and without hysteresis. Because of the excellent repeatability and stability of the results, it is conceived that miniaturized temperature sensors could be designed using such aligned multiwalled nanotube films.     

Charge transfer induced polarity switching in carbon nanotube transistors

We probed the charge transfer interaction between the amine-containing molecules hydrazine, polyaniline, and aminobutyl phosphonic acid and carbon nanotube field effect transistors (CNTFETs). We successfully converted p-type CNTFETs to n-type and drastically improved the device performance in both the ON- and OFF-transistor states, utilizing hydrazine as dopant. We effectively switched the transistor polarity between p- and n- type by accessing different oxidation states of polyaniline. We also demonstrated the flexibility of modulating the threshold voltage (Vth) of a CNTFET by engineering various charge-accepting and -donating groups in the same molecule.     

Highly conductive interwoven carbon nanotube and silver nanowire transparent electrodes

Abstract

Electrodes fabricated using commercially available silver nanowires (AgNWs) and single walled carbon nanotubes (SWCNTs) produced sheet resistances in the range 4–24 Ω □^?1 with specular transparencies up to 82 %. Increasing the aqueous dispersibility of SWCNTs decreased the bundle size present in the film resulting in improved SWCNT surface dispersion in the films without compromising transparency or sheet resistance. In addition to providing conduction pathways between the AgNW network, the SWCNTs also provide structural support, creating stable self-supporting films. Entanglement of the AgNWs and SWCNTs was demonstrated to occur in solution prior to deposition by monitoring the transverse plasmon resonance mode of the AgNWs during processing. The interwoven AgNW/SWCNT structures show potential for use in optoelectronic applications as transparent electrodes and as an ITO replacement.     

Evidence of sequential lift in growth of aligned multiwalled carbon nanotube multilayers

We synthesized aligned multiwalled carbon nanotube multilayers by aerosol-assisted catalytic chemical vapor deposition through sequential injections of aerosols containing both carbon and catalyst precursors. Each sequence was traced by a specific duration or precursor mixture, with the carbon source being possibly enriched in (13)C isotope labels. We discovered that any sequence involved the growth of a new layer on the substrate surface, under any pre-existing one by lifting it up, giving definitive evidence of a base-growth mechanism.     

Dispersion control and characterization in multiwalled carbon nanotube and phenylethynyl-terminated imide composites

The inherent multifunctional properties of carbon nanotubes provide an opportunity to create novel composites, but their dispersion into a polymer matrix is challenging due to nanotube dimensions, interparticle forces, and poor interaction with the polymer. In this study, we used melt mixing to disperse multiwalled carbon nanotubes (MWNTs) in a polyimide resin under various process conditions to understand the efficacy of the process and the energy required to achieve dispersion and distribution. Through controlled variation of process conditions, we achieved various degrees of nanotube dispersion and distribution. The different dispersion and distribution states were observed by microscopy and correlated with the magnitude of the changes seen in the glass transition temperature and viscosity when compared to the neat resin. The results of these studies will be used to assess the compatibility of nanocomposite resins with composite fabrication methods and predict appropriate processing conditions for producing multiscale composites.     

Electric field induced, superhydrophobic to superhydrophilic switching in multiwalled carbon nanotube papers

Superhydrophobic multiwalled carbon nanotube bucky paper, fabricated after ozonolysis, shows fascinating electrowetting behavior, which could be remarkably tuned by changing key solution variables like the ionic strength, the nature of the electrolyte, and the pH of the water droplet. More significantly, the droplet behavior can be reversibly switched between superhydrophobic, Cassie-Baxter state to hydrophilic, Wenzel state by the application of an electric field, especially below a threshold value.     

Fast mass transport through carbon nanotube membranes

The May 19, 2006 issue of Science included a paper by Holt et al. on "Fast Mass Transport Through Sub-2-Nanometer Carbon Nanotubes". The paper was also featured on the cover, showing methane molecules translating inside a carbon nanotube (CNT). The authors explained how they prepared 2-6-mum thin membranes consisting of double-walled carbon nanotubes (DWNTs) all aligned perpendicular to the apparent membrane surface. These tubes are open at both ends and the space between the tubes is filled with dense Si(3)N(4). Pure gas and water fluxes were measured at room temperature with the application of a small pressure difference. Interpretation of the results led to the conclusion that the membranes showed much higher fluxes than what was estimated from Knudsen gas diffusion and Poiseuille viscous flow models. The membranes have a straight-channel morphology with a narrow pore-size distribution and exceptionally smooth pore walls. The unusual geometry and surface properties make it difficult to compare the membrane's properties with common membranes but there is no question that the mass transport in the aligned DWNTs is fast indeed. To appreciate how fast, we will consider their transport properties starting from the perspective of "conventional" porous membrane technology. Recent molecular dynamics simulations suggest that none of the classic models for gas (Knudsen) and water (Poiseuille) permeation work in a meaningful way for these nanotube membranes, and new models are needed.     

Electron transport through metal-multiwall carbon nanotube interfaces

In this paper, we examine mechanisms of electron transport across the metal-carbon nanotube (CNT) interface for two different types of multiwall carbon nanotube (MWNT) architectures, horizontal or side-contacted MWNTs and vertical or end-contacted MWNTs. Horizontally aligned nanotube growth and electrical characteristics are examined with respect to their potential applications in silicon-based technologies. Recent advances in the synthesis techniques of vertical MWNTs have also enhanced the possibility for a manufacturable solution incorporating this novel material as on-chip interconnects or vias as copper interconnect feature sizes are scaled into the sub-100-nm regime. A vertical MWNT architecture is presented that may be suitable for integration into silicon-based technologies. The growth method for this architecture and its effect on electrical characteristics are examined. Through simulations, dc measurements, and comparison of our results with previous studies, we explain why high contact resistance is observed in metal-CNT-metal systems.     

Performance of superconducting nanowire single photon detection system with different temperature variation

The performance of cryocooler-based superconducting single photon detection system suffers from the intrinsic temperature oscillation, which is typically ∼300 mK around 4.2 K originated from the periodic expansion of the cryocooler’s working fluid (He). By using a rare-earth alloy (ErNi) plate with a high heat capacity at cryogenic temperatures in between the cold head of the cryocooler and the detector block, the detector temperature variation is successfully damped to be less than 10 mK. The dark count rate is reduced and the maximum working bias current is increased. The quantum efficiency of SNSPD system is significantly improved by 40%.