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Record-long (21.7 mm) vertically aligned MWNT arrays were synthesized using water-assisted thermal CVD process. The catalyst lifetime was maintained for 790 min at optimized experimental condition. The growth of the centimeter long CNT was observed by real time photography at different growth conditions. The growth length increased linearly with increasing growth time followed by a sudden growth end. The ratio of ethylene and H 2 concentration as well as the water and ethylene concentration was studied and optimized which led to prolong catalyst lifetime. Transmission electron microscope images confirmed that most CNTs were double wall and the number of wall distribution was uniform along different height position. Raman spectra showed that the I D / I G ratio remained constant at the 3 studied positions along the CNT. TGA demonstrated negligible impurity incorporation in the CNT array.

The mechanism of abrupt growth termination for growing vertically aligned centimeter long CNT arrays in chemical vapor deposition process was studied. We found that the growth length increases linearly with increasing growth time and the CNT growth terminates abruptly for all the experimental conditions applied. We investigated the change of particle size distribution, particle number density and the catalyst composition on the surface of the substrate with the exposure time and temperature in the reactor. For this study X-ray Photoelectron Spectroscopy (XPS), High Resolution Transmission Electron Microscopy (HRTEM) and Atomic Force Microscopy (AFM) were employed. Focused Ion Beam (FIB) was used for preparation of the STEM samples. The experimental results demonstrated that the formed catalyst nanoparticles undergo compositional and morphological changes during the heating step of the substrate, when the temperature of the reactor is rising from ambient to the growth temperature, and during annealing at the set growth temperature. Most of the changes in the catalyst composition and morphology were related to metal diffusion into neighboring substrate layers during heating up to the growth temperature. Based on the results, a new scenario of abrupt termination mechanism for growing centimeter long CNT arrays using an iron–gadolinium binary catalyst was proposed.

Individual carbon nanotubes (CNTs) have exceptional mechanical, thermal and electrical properties. However, transferring these extraordinary qualities into CNT assemblages, without degrading performance, remains a challenge. At the UC Nanoworld Laboratories, we are successfully working to complete the cycle of synthesis, processing and application of carbon nanostructured materials. This approach allows for tuning of the CNT products at different processing stages in order to meet specific application objectives. Results in catalytic synthesis of centimeter long CNT arrays by CVD and related kinetics data will be presented, along with their characterization. Nanotechnology innovations under development in our Nanoworld laboratories include: big area synthesis of arrays and processing this highly aligned and pure CNT material into light, strong and electrically conductive threads and sheets. CNT thread with electrical resistivity of about 10− 6 Ω ∗ m has been produced. In addition, optical and Electromagnetic Interference (EMI) shielding, shielding properties of CNT sheets will be reported. These CNT materials have been fully characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), which revealed the outstanding alignment of the nanotubes. Raman Spectroscopy and Thermo-Gravimetric Analysis (TGA) confirmed the high purity of the CNT threads and sheets. The reported properties open opportunities for novel applications of the CNT assemblages such as power distribution, sensors, transparent conductive electrodes, EMI shielding, nano-composites, biomedical devices, etc.

A multiwalled carbon nanotube (MWCNT)-based electrochemical biosensor is developed for monitoring microcystin-LR (MC-LR), a toxic cyanobacterial toxin, in sources of drinking water supplies. The biosensor electrodes are fabricated using vertically well-aligned, dense, millimeter-long MWCNT arrays with a narrow size distribution, grown on patterned Si substrates by water-assisted chemical vapor deposition. High temperature thermal treatment (2500 ° C) in an Ar atmosphere is used to enhance the crystallinity of the pristine materials, followed by electrochemical functionalization in alkaline solution to produce oxygen-containing functional groups on the MWCNT surface, thus providing the anchoring sites for linking molecules that allow the immobilization of MC-LR onto the MWCNT array electrodes. Addition of the monoclonal antibodies specifi c to MC-LR in the incubation solutions offers the required sensor specifi city for toxin detection. The performance of the MWCNT array biosensor is evaluated using micro-Raman spectroscopy, including polarized Raman measurements, X-ray photoelectron spectroscopy, cyclic voltammetry, optical microscopy, and Faradaic electrochemical impedance spectroscopy. A linear dependence of the electron-transfer resistance on the MC-LR concentration is observed in the range of 0.05 to 20 μ g L − 1 , which enables cyanotoxin monitoring well below the World Health Organization (WHO) provisional concentration limit of 1 μ g L − 1 for MC-LR in drinking water.

Towers of aligned multiwalled carbon nanotubes (MWCNTs) were electrochemically oxidized in aqueous 1 M NaOH. An oxidation current that decayed with time was monitored using amperometry at a fixed potential. Cyclic voltammetry showed that the background current and electrode capacitance increased after oxidation without significantly affecting the faradaic current from the reduction of ferricyanide. Oxidation in NaOH caused morphological changes and increased hydrophilicity of the MWCNT tower electrodes. XPS spectra indicated increased oxygen on the surface after oxidation, while Raman spectra indicated that a large amount of amorphous carbon was present before and after oxidation.

Vertically aligned multi-walled carbon nanotube (MWCNT) arrays up to ∼6 mm high with an array density of 0.06 g cm−3 have been grown by chemical vapor deposition. Thermal conductivities (κ) and electrical conductivities (σ) were determined from 5 K to 390 K. The range for κ at 300 K is 0.5–1.2 W m−1 K−1 along the tube growth direction, with the shortest array having the highest κ, and an order of magnitude lower in the direction perpendicular to the tubes. The same trends also were evident for electrical conductivity, i.e., decreasing values with increasing array height and conductivity an order of magnitude lower in the perpendicular direction. Values of σ ranged from 7 to 14 S cm−1 along the array at 300 K. The Seebeck coefficient is ∼20 μV K−1 at 300 K. The effective Lorentz number indicates that thermal conductivity in the carbon nanotube arrays is phonon dominated over the full temperature range.

Individual nanotubes made of carbon, boron nitride, iron, silicon, or other materials have properties such as high strength, toughness, electrical and thermal conductivity, and light weight that cannot be matched by conventional materials. Nanotubes also change their properties in response to external fields and change one type of energy into another, which are useful for design. This article explores three main steps in exploiting responsive materials based on nanotubes: nanotube synthesis, macroscale material fabrication, and incorporation into device structures for novel applications. Nanotubes are always synthesized as individual particles in the form of powders, smoke particles, or aligned forests. To be industrially important, nanotubes generally must be processed to form derivative materials such as functionalized/coated powders and forests and macroscale intermediate materials such as sheets, ribbon, and yarn. The processed nanotubes are then used to develop responsive materials and devices that are able to resist, react to, or generate energy from their environment. This article provides background information and ideas on how to develop nanotube responsive materials for everyday use.

A self-aligned nanogap between multiple metal layers has been developed using a new controlled undercut and metallization technique (CUMT), and practically applied for self-assembly of individual carbon nanotubes (CNTs) over the developed nanogap. This new method allows conventional optical lithography to fabricate nanogap electrodes and self-aligned patterns with nanoscale precision. The self-aligned nickel (Ni) pattern on the nanogap electrode works as an assembly spot where the residual iron (Fe) catalyst at the end of the CNT is magnetically captured. The captured CNT is forced to be aligned parallel to the flow direction by fluidic shear force. The combined forces of magnetic attraction and fluidic alignment provide massive self-assembly of CNTs at target positions. Both multiwalled nanotubes (MWNTs) and single walled nanotubes (SWNTs) were successfully assembled over the nanogap electrodes, and their electrical characteristics were fully characterized. The CNTs self-assembled on the developed electrodes with a nanogap and showed a very reliable and reproducible current-voltage (I-V) characteristic. The method developed in this work can envisage the mass fabrication of individual CNT-assembled devices which can be applied to nanoelectronic devices or nanobiosensors.

Carbon nanotubes (CNTs) are fascinating materials with outstanding mechanical, optical, thermal, and electrical properties [1-4]. CNTs also have a huge aspect ratio and a large sur‐ face area to volume ratio. Because of their unique properties, vertically aligned centimeter long CNT arrays have generated great interest for environmental sensors, biosensors, spin‐ ning CNT into yarn, super-capacitors, and super-hydrophobic materials for self-cleaning surfaces [5-11]. Yun et al. studied a needle-type biosensor based on CNTs to detect dopa‐ mine. Their results showed advantages of using CNT biosensors for detecting neurotrans‐ mitters [11]. Most of the envisioned applications require CNTs with high quality, a long length, and well aligned vertical orientation. Although many researchers have studied the synthesis of vertically aligned CNT arrays, the CNT growth mechanism still needs to be bet‐ ter understood. In addition, CNT lengths are typically limited to a few millimeters because the catalyst lifetime is usually less than one hour [1216]. Many groups have studied the ki‐ netics of CNT growth trying to improve CNT properties. Different observation methods [17-22] were used to determine the effect of the catalyst, buffer layers, carbon precursor, and deposition conditions on nanotube growth. One of the suggested growth mechanisms pos‐ tulates several steps [23]. First, the carbon source dissociates on the surface of the substrate. Next, the carbon atoms diffuse to the molten catalyst islands and dissolve. The metal-carbon solution formed reaches a supersaturated state. Finally, the carbon nanotubes start to grow from the carboncatalyst solution. In situ observation of CNTs during their nucleation and growth is a useful method to understand the growth mechanism, which might help to over‐ come the limitation of the short length of nanotubes, and to control array growth and quali‐ ty. Various remarkable approaches of in situ observation have been performed to affirm the growth mechanism of vertically aligned CNTs and also to obtain kinetics data such as

Self-consistent formulae for treating the pi-polarization waves in two-beam X-ray diffraction from single crystals are refined within the Laue formalism. These formulae overcome the inverted Delta.D not equal 0 problem and avoid all the unnecessary approximations in previous dynamical theories. Therefore, they are as accurate as the formulae for sigma-polarization waves.

The electrical resistivity of CNT yarns of diameters 10–34 μm, spun from multi-walled carbon nanotube arrays, have been determined from 2 to 300 K in magnetic fields up to 9 T. The magnetoresistance is large and negative at low temperatures. The thermal conductivity also has been determined, by parallel thermal conductance, from 5 to 300 K. The room-temperature thermal conductivity of the 10 μm yarn is (60 ± 20) W m −1 K −1 , the highest measured result for a CNT yarn to date. The thermal and electrical conductivities both decrease with increasing yarn diameter, which is attributed to structural differences that vary with the yarn diameter.