Dali Qian

Load transfer and deformation mechanisms in carbon nanotube-polystyrene composites

Multiwall carbon nanotubes have been dispersed homogeneously throughout polystyrene matrices by a simple solution-evaporation method without destroying the integrity of the nanotubes. Tensile tests on composite films show that 1 wt % nanotube additions result in 36%–42% and ∼25% increases in elastic modulus and break stress, respectively, indicating significant load transfer across the nanotube-matrix interface. In situ transmission electron microscopy studies provided information regarding composite deformation mechanisms and interfacial bonding between the multiwall nanotubes and polymer matrix.

Continuous production of aligned carbon nanotubes: a step closer to commercial realization

High-purity aligned multi-walled carbon nanotubes MWNTs were synthesized through the catalytic decomposition of a ferrocene-xylene mixture at ; 6758C in a quartz tube reactor and over quartz substrates, with a conversion of ; 25% of the total hydrocarbon feedstock. Under the experimental conditions used, scanning electron microscope images reveal that the MWNT array grows perpendicular to the quartz substrates at an average growth rate of ; 25 mmrh. A process of this nature which does not require preformed substrates, and which operates at atmospheric pressure and moderate temperatures, could be scaled up for continuous or semi-continuous production of MWNTs. q 1999 Elsevier Science B.V. All rights reserved.

Model of carbon nanotube growth through chemical vapor deposition

Abstract This Letter outlines a model to account for the catalyzed growth of nanotubes by chemical vapor deposition. It proposes that their formation and growth is an extension of other known processes in which graphitic structures form over metal surfaces at moderate temperatures through the decomposition of organic precursors. Importantly, the model also states that the form of carbon produced depends on the physical dimensions of the catalyzed reactions. Experimental data are presented that correlate nanotube diameters to the size of the catalyst particles. Nanotube stability as a function of nanotube type, length and diameter are also investigated through theoretical calculations.

Purification and structural annealing of multiwalled carbon nanotubes at graphitization temperatures

In this work, we present a systematic study of the effects of graphitization on the structural perfection of multiwalled carbon nanotubes. High purity nanotubes were produced by a low temperature CVD method and subsequently annealed at temperatures between 1600 and 3000°C. The nanotubes were characterized for chemical purity, interlayer spacing, and defect healing. The graphitization procedure was found to remove residual metal catalyst in the nanotubes and reduce the wall defects as reflected in a reduced interlayer spacing between the graphene shells. Graphitization presents a low-cost, commercially viable method of purifying and ordering multiwall carbon nanotubes.

Magnetoelastic sensors in combination with nanometer-scale honeycombed thin film ceramic TiO2 for remote query measurement of humidity

Ribbonlike magnetoelastic sensors can be considered the magnetic analog of an acoustic bell; in response to an externally applied magnetic field impulse the sensors emit magnetic flux with a characteristic resonant frequency. The magnetic flux can be detected external to the test area using a pick-up coil, enabling query remote monitoring of the sensor. The characteristic resonant frequency of a magnetoelastic sensor changes in response to mass loads. [L.D. Landau and E. M. Lifshitz, Theory of Elasticity, 3rd ed. (Pergamon, New York, 1986). p. 100].Therefore, remote query chemical sensors can be fabricated by combining the magnetoelastic sensors with a mass changing, chemically responsive layer. In this work magnetoelastic sensors are coated with humidity-sensitive thin films of ceramic, nanodimensionally porous TiO2 to make remote query humidity sensors.

Thin film metallic catalyst coatings for the growth of multiwalled carbon nanotubes by pyrolysis of xylene

Thin film metallic coatings applied to alumina and silicon substrates are investigated for their use as a catalyst to help grow high-quality multiwall carbon nanotubes (MWNTs). Substrate coatings examined include Fe, Tb:Fe, Ni, Cu, and Ni:Fe, with xylene used as the hydrocarbon source. Coating the substrate with Tb90Fe10 and Ni80Fe20 facilitated dense and uniform growth of MWNTs without graphitic particles; Ni and Fe substrate coatings produced graphitic particles in addition to the MWNTs, while Tb and Cu were found to be completely inactive with no MWNT growth. Many of the MWNTs grown over Ni:Fe have a helical appearance, while the MWNTs grown over Tb90Fe10 did not contain catalyst particles

Visible photoluminescence from ruthenium-doped multiwall carbon nanotubes

Visible photoluminescence at 515 nm of ruthenium-doped multiwall carbon nanotubes, fabricated on quartz substrates using a chemical vapor deposition technique, is reported. The well-aligned nanotubes serve as templates for the luminescent, residual ruthenium–iron catalyst particles contained within the nanotubes, restricting the particle size to about 10 nm. The synthesis technique can be readily extended to other luminescent dopants; moreover, since nanotube arrays can be readily grown from patterned substrates, nanotube-based optoelectronic devices may be achieved.

Determination of Carrier Densities of Boron- and Nitrogen-Doped Multiwalled Carbon Nanotubes Using Mott–Schottky Plots

Knowledge of the carrier type (p- or n-type) and the carrier density of carbon nanotubes is critical in semiconductor applications such as thermoelectric power generation and Peltier cooling. In this paper, an experimental procedure for electrochemically characterizing multiwalled carbon nanotubes (MWCNTs) doped with boron or nitrogen has been presented. The carrier type and carrier density of the doped MWCNTs were determined by generating Mott-Schottky plots. The boron-doped nanotubes were synthesized using the substitution reaction method and the nitrogen-doped MWCNTs were synthesized using the continuous-feed chemical vapor deposition (CVD) method using pyridine or acetonitrile as the carbon precursor and ferrocene as the metal catalyst particle precursor. The nitrogen-doped nanotubes were synthesized at different CVD reaction temperatures: 650, 700, 800, and 900°C, and the effect of reaction temperature on the carrier densities of the carbon nanotubes was examined. Thermoelectric devices were constructed using pyridine nanotubes synthesized at different synthesis temperatures, and it was found that with any change (increase/decrease) in the carrier densities reflected a corresponding change in the thermoelectric power of the nanotubes.

Tearing open nitrogen-doped multiwalled carbon nanotubes

Reductive alkylation of N-MWNTs with Li/NH3 results in fracturing of the nanotubes, ripping channels that breach the central core and generating significant new pore volume.

Synthesis of Germanium/Multi-Walled Carbon Nanotube Core-Sheath Structures via Chemical Vapor Deposition

One-dimensional (1D) nanostructures such as nanotubes, nanowires, and nanobelts have been the focus of much recent attention, owing to the novel electronic and optical properties intrinsically associated with their low dimensionality and the quantum confinement effect. Such 1D nanostructures have potential applications in nanoelectronics, advanced composites, field emission devices, sensors, probes, optics and optoelectronics (Baughman et al., 2002; Agarwal & Lieber, 2006). Silicon nanowires have been preferentially studied since Si is of great technological importance in microelectronics (Morales & Lieber, 1998). Silicon nanowires exhibit significant differences in physical (Cui & Lieber 2001; Ma, et al., 2003; Sun et al., 2001) and chemical properties (Sun et al., 2003; Chen et al., 2005) from bulk Si, which have been exploited to fabricate nanoelectronic devices such as logic circuits (Huang et al., 2001), field effect transistors (Lieber, 2003), and sensors (Cui et al., 2001). Compared to Si, Ge nanostructures are of particular interest, since the exciton Bohr radius of bulk Ge (24.3 nm) (Maeda et al., 1991) is larger than that of Si (4.9 nm) (Cullis et al., 1997), resulting in more prominent quantum confinement effects. Ge also offers the advantage of lower processing temperatures with easier integration into conventional devices. Furthermore, Ge has much higher electron and hole mobility than Si (Sze, 1981), which is especially required when electronic devices are scaled down to the sub-100 nm regime. Several growth methods have been developed for the synthesis of Ge nanowires, including laser ablation (Morales & Lieber, 1998; Zhang et al., 2000), thermal evaporation (Gu et al., 2001; Nguyen et al., 2005; Sun et al., 2006; Das et al., 2007; Sutter et al., 2008), supercriticalfluid synthesis (Ryan et al., 2003; Polyakov et al., 2006; Ziegler et al., 2004; Erts et al., 2006), liquid-state synthesis (Heath & LeGoues, 1993; Song et al., 2009), molecular beam epitaxy (Omi & Ogino, 1997), and chemical vapor deposition (CVD) (Kodambaka et al., 2007; Ryan et al., 2003). CVD has been the most widely employed of these synthesis methods, with the aim of synthesizing Ge nanowires in a controllable way via the selection of suitable Ge