Investigation of Field Emission and Photoemission Properties of High-Purity Single-Walled Carbon Nanotubes Synthesized by Hydrogen Arc Discharge

Enhanced field emission and improved supercapacitor obtained from plasma-modified bucky paper

The surface morphology of bucky papers (BPs) made from single-walled carbon nanotubes (CNTs) is modified by plasma treatment resulting in the formation of vertical microstructures on the surface. The shapes of these structures are either pillarlike or conelike depending on whether the gas used during plasma treatment is Ar or CH(4) . A complex interplay between different factors, such as the electric field within the plasma sheath, polarization of the CNT, intertubular cohesive forces, and ion bombardment, result in the formation of these structures. The roles played by these factors are quantitatively and qualitatively analyzed. The final material is flexible, substrate-free, composite-free, made only of CNTs, and has discrete vertically aligned structures on its surface. It shows enhanced field emission and electrochemical charge-storage capabilities. The field enhancement factor is increased by 6.8 times, and the turn-on field drops by 3.5 times from an initial value of 0.35 to 0.1 V μm(-1) as a result of the treatment. The increase in Brunauer-Emmett-Teller surface area results in about a fourfold improvement in the specific capacitance of the BP electrodes. Capacitance values before and after the treatments are 75 and 290 F g(-1) , respectively. It is predicted that this controlled surface modification technique could be put to good use in several applications based on macroscopic CNT films.

The effect of pre-treatment methods on morphology and size distribution of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) are important materials with a unique combination of mechanical, electrical and thermal properties. MWCNTs usually exist as tangled aggregates embedding impurities such as catalysts or amorphous carbon. Therefore, purification and cutting process are essential processes to get the well-dispersed solutions in solvents or a polymer matrix for diverse practical applications. In this study, we used MWCNTs with high purity (>95%) and focused on the cutting effects on the size distribution of MWCNTs. Their size distribution after the cutting process is expected to be a very important factor in determining the final properties of the polymer-MWCNT composite. Gel permeation chromatography (GPC) was effectively demonstrated in analyzing the effect of treatment methods on a size distribution of pre-treated MWCNTs in organic solvent. MWCNT was treated by two different methods. One is an oxidation process with H(2)SO(4)/HNO(3) solution and the other is an ultrasonic process with high power. MWCNTs were shortened simply by applying high power ultrasonication with narrow length distribution. Meanwhile, the acid-treated MWCNTs became much broader in their sizes and more flexible in their rigidities. These differences led to a different behavior in electric conductivity. These studies promise to optimize pre-treatment processes for tailoring suitable MWCNTs towards future applications.