We have demonstrated a scalable approach to synthesize single-walled carbon nanotubes (SWCNTs) with selected diameter distributions by applying a magnetic field perpendicular to the electric field in the arc plasma. It is found that the purity and orientation of SWCNTs can be controlled by the magnetic field. SWCNTs with different diameter distributions can be separated into two different regions by the applied magnetic field, and the diameter-selection efficiency is improved by modifying the direction of the magnetic field. Our findings suggest that the motion of the catalyst particles with different sizes, positive carbon ions and electrons are significantly influenced by Lorentz forces, resulting in the difference in the growth processes of the SWCNTs due to the collective interactions between the arc plasma and the magnetic field.

Direct current (DC) arc discharge method gives high temperature in a short time, which has been widely used to prepare carbon nanotubes. We use this simple approach to synthesize magnesiumoxide (MgO) nanocubes without any catalyst. Structural characterizations indicate that the as-synthesized MgO nanocubes are all single crystalline, and enclosed by {100} facets. The edge lengths mainly range from 60 nm to 100 nm. Most nanocubes interlace with adjacent nanocubes as three types: point contacts, line contacts and face contacts. The blue band in PL spectrum is ascribed to various structural defects, the nanosize effect and surface states of MgO nanocubes.

We report unusual negative thermal expansion and viscoelastic properties in graphene oxide paper. The paper was prepared from aqueous GO dispersions using a simple vacuum evaporation technique. From room temperature to 150 °C, this paper-like graphene oxide sheet exhibits a constant negative thermal expansion coefficient of −67 × 10−6/°C along the in-plane direction. Peculiar hysteresis loops of thermal expansion-temperature curves are observed, which are affected by the cooling rate and starting temperature of cooling. The tensile tests on GO paper show clear hysteresis loops, revealing the viscoelastic property of the paper. The viscoelastic properties show excellent frequency-stability in the range of 1.0–60 Hz. In the low temperature range −150 to 25 °C, however, they show a strong temperature dependence. The storage modulus of the graphene oxide paper continuously increases with decreasing temperature.

Diameter selective growth of single-walled carbon nanotubes (SWCNTs) is one of the most important challenges for the application of SWCNTs in future high-performance nanodevices. In this investigation, SWCNTs with selective diameters have been synthesized by DC arc discharge method, in which carbon monoxide (CO) mixed with helium were used as buffer gases. The experimental results show that SWCNTs with small diameters are preferentially etched with the increase of CO concentration. However, pure CO as buffer gas can result in the formation of carbon nanoparticles. Appropriate CO pressure (>8 kPa) gives the diameter selective growth of SWCNTs in the range of 1.5–1.7 nm.

Single-walled carbon nanotubes with controlled length distributions have been successfully achieved by changing the cathode diameter in the arc discharge process. We find that the purities of SWNT products and the crystallinity of SWNTs are improved by using the cathode with certain diameter. By simply increasing the cathode diameter from 0.8 to 2.0 cm, the most abundant length fractions of SWNTs increase from 1.2 to 1.8 μm. On the other hand, the diameter distributions of SWNTs are also influenced by changing cathode diameter, ascribing to the changes in SWNT nucleation and growth processes caused by different plasma densities and temperature distributions. This approach would enable a viable route towards the synthesis of SWNTs with targeted length through the tuning of cathode diameter.

We report a facile and scalable approach to synthesize single-walled carbon nanotubes (SWNTs) with selected diameter distribution by applying a magnetic field perpendicular to the electric field in the arc plasma region. It is found that this magnetic field-induced diameter-selectivity strategy enables the control of the SWNTs with different diameter distributions in different regions, and the diameterselective efficiency could be enhanced by modifying the direction of magnetic field. Our results indicate that the motions of the catalysts with different particle sizes, positive carbon ions and electrons are significantly influenced by the magnetic field and electromagnetic force, resulting in the different nucleation and growth processes of SWNTs due to the collective interactions between the magnetic field and arc plasma. This approach would enable a viable route towards the synthesis of SWNTs with desired diameter through the tuning of arc parameters in the arc discharge process.

Carbon nanowires with a diameter of 40–60 nm were synthesized by coating single-walled carbon nanotubes (SWCNTs) in an intermittent, one-stage DC arc discharge process. Transmission electron microscopy shows that these nanowires consist of a SWCNT with an amorphous carbon coating, whose thickness depends on the time of arc discharge. The mechanical properties of blocks of these nanowires were tested by load–unload cyclic compression and static force thermomechanical experiments. The results show that carbon nanowire blocks exhibit better compressive behavior than pure SWCNTs blocks, and carbon nanowires show a typical nonlinear strain–temperature response due to the amorphous carbon layer. A mechanism of adsorption-controlled growth of amorphous carbon on the SWCNTs in the vapor phase is proposed for the formation of the nanowires.

Magnesium oxide (MgO) nanowires have been synthesized by DC arc discharge without using metal catalysts. These MgO nanowires are singlecrystalline, with an axes along the [100] direction. The cross sectional diameter of the nanowires spans the range of 5–150 nm, with the length up to hundreds of micrometers. The growth of MgO nanowires can be considered as a vapor-phase chemical reaction process, in which both defects and oxygen partial pressure play important roles. The photoluminescence (PL) measurement reveals two emission bands centered at 437 and 496 nm, which can be ascribed to various structural defects and nanosize effect of MgO nanowires. This efficient synthesis method has the potential for large-scale preparation of metal oxide nanostructures, using metals with low melting-points as the raw materials.