Qunqing Li

Nanotechnology: Spinning continuous carbon nanotube yarns

The creation of continuous yarns made out of carbon nanotubes would enable macroscopic nanotube devices and structures to be constructed. Here we show that carbon nanotubes can be self-assembled into yarns of up to 30 cm in length simply by being drawn out from superaligned arrays of carbon nanotubes, and that the strength and conductivity of these yarns can be enhanced by heating them at high temperatures. Our findings should help to translate the remarkable mechanical, electrical and thermal properties of carbon nanotubes to a macroscopic scale.

Fabrication of ultralong and electrically uniform single-walled carbon nanotubes on clean substrates.

We report the controlled growth of ultralong single-wall carbon nanotube (SWNT) arrays using an improved chemical vapor deposition strategy. Using ethanol or methane as the feed gas, monodispersed Fe-Mo as the catalyst, and a superaligned carbon nanotube (CNT) film as the catalyst supporting frame, ultralong CNTs over 18.5 cm long were grown on Si substrates. The growth rate of the CNTs was more than 40 mum/s. No catalyst-related residual material was found on the substrates due to the use of a CNT film as the catalyst supporting frame, facilitating any subsequent fabrication of SWNT-based devices. Electrical transport measurements indicated that the electrical characteristics along a single ultralong SWNT were uniform. We also found that maintaining a spatially homogeneous temperature during the growth process was a critical factor for obtaining constant electrical characteristics along the length of the ultralong SWNTs.

Flexible, Stretchable, Transparent Carbon Nanotube Thin Film Loudspeakers

We found that very thin carbon nanotube films, once fed by sound frequency electric currents, could emit loud sounds. This phenomenon could be attributed to a thermoacoustic effect. The ultra small heat capacity per unit area of carbon nanotube thin films leads to a wide frequency response range and a high sound pressure level. On the basis of this finding, we made practical carbon nanotube thin film loudspeakers, which possess the merits of nanometer thickness and are transparent, flexible, stretchable, and magnet-free. Such a single-element thin film loudspeaker can be tailored into any shape and size, freestanding or on any insulating surfaces, which could open up new applications of and approaches to manufacturing loudspeakers and other acoustic devices.

Controlled Fabrication of High-Quality Carbon Nanoscrolls from Monolayer Graphene

We report a simple and effective way of fabricating high-quality carbon nanoscrolls (CNSs), using isopropyl alcohol solution to roll up monolayer graphene predefined on SiO(2)/Si substrates. Transmission electron microscopy studies reveal that the CNS has a tube-like structure with a hollow core surrounded by graphene walls 0.35 nm apart. Raman spectroscopy studies show that the CNS is free of significant defects, and the electronic structure and phonon dispersion are slightly different from those of two-dimensional graphene. Finally, the CNS-based device is fabricated, directly on the SiO(2)/Si substrate. Electrical-transport measurements show that its resistance is weakly gate-dependent but strongly temperature-dependent. In addition, the CNS can sustain a high current density up to 5 x 10(7) A/cm(2), indicating that it is a good candidate for microcircuit interconnects. The controlled fabrication of high-quality CNSs may open up new opportunities for both fundamental and applied research of CNSs.

Continuous synthesis and characterization of silicon carbide nanorods

Abstract A two-step reaction scheme has been employed for the synthesis of SiC nanorods at 1400°C. SiO vapour was generated via the silicon reduction of silica, and then this SiO vapor reacted with carbon nanotubes to form SiC nanorods. The morphology and structure of the nanorods were characterized by XRD, TEM, IR and Raman spectroscopy. The nanorods are single crystalline β-SiC with the diameters ranging from 3 to 40 nm. A broad photoluminescence peak located around 430 nm under 260 nm UV fluorescent light excitation at room temperature is observed. A growth model of SiC nanorods is proposed.

Binder‐Free LiCoO2/Carbon Nanotube Cathodes for High‐Performance Lithium Ion Batteries

Binder-free LiCoO(2) -SACNT cathodes with excellent flexibility and conductivity are obtained by constructing a continuous three-dimensional super-aligned carbon nanotube (SACNT) framework with embedded LiCoO(2) particles. These binder-free cathodes display much better cycling stability, greater rate performance, and higher energy density than classical cathodes with binder. Various functional binder-free SACNT composites can be mass produced by the ultrasonication and co-deposition method described in this paper.

Synthesis of silicon nitride nanorods using carbon nanotube as a template

A method to prepare silicon nitride nanoscale rods using carbon nanotube as a template has been presented in this letter. The products of the reaction of carbon nanotubes with a mixture of Si and SiO2 powder in nitrogen atmosphere are β-Si3N4, α-Si3N4, and Si2N2O nanorods. The sizes of the nanorods are 4–40 nm in diameter and up to several microns in length. The formation mechanism of the nanorods has also been discussed.

Highly Sensitive Surface-Enhanced Raman Scattering Substrate Made from Superaligned Carbon Nanotubes

Surface-enhanced Raman scattering (SERS) has attracted wide attention because it can enhance normally weak Raman signal by several orders of magnitude and facilitate the sensitive detection of molecules. Conventional SERS substrates are constructed by placing metal nanoparticles on a planar surface. Here we show that, if the planar surface was substituted by a unique nanoporous surface, the enhancement effect can be dramatically improved. The nanoporous surface can be easily fabricated in batches and at low costs by cross stacking superaligned carbon nanotube films. The as-prepared transparent and freestanding SERS substrate is capable of detecting ambient trinitrotoluene vapor, showing much higher Raman enhancement than ordinary planar substrates because of the extremely large surface area and the unique zero-dimensional at one-dimensional nanostructure. These results not only provide a new approach to ultrasensitive SERS substrates, but also are helpful for improving the fundamental understanding of SERS phenomena.

Measuring the Work Function of Carbon Nanotubes with Thermionic Method

The work function of carbon nanotubes might depend on their diameters and the number of walls, and be different for their tips and sidewalls. Here we report the work function measurement of single-walled, double-walled, and multiwalled carbon nanotubes by investigating the thermionic emission from the middle of their bundles. It is found that the sidewall work functions of the three kinds of carbon nanotubes are all around 4.7-4.9 eV; the diameter and the numbers of walls have no obvious influence on their work functions. For the carbon nanotube bundle with some tips appearing in the middle, the measured work function is smaller than without tips, indicating that the work function of tips is smaller than that of the sidewalls. This tip effect also results in a difference in the thermionic emission characteristic, implying non-uniform work function distribution along the bundle.

Fano resonances in dipole-quadrupole plasmon coupling nanorod dimers

We theoretically investigate the plasmon coupling in metallic nanorod dimers. A pronounced dip is found in the extinction spectrum due to plasmonic Fano resonance, which is induced by destructive interference between the bright dipole plasmon of a short nanorod and the dark quadrupole plasmon of a long nanorod. This Fano interference can also be explained as the coupling between the bright and dark modes both supported by the whole dimer. The Fano resonance can be tuned by adjusting the spatial or spectral separation between two nanorods in the dimer.