Synthesis of straight multi-walled carbon nanotubes by arc discharge in air and their field emission properties

The possibility of preparing straight multi-walled carbon nanotubes (MWCNTs) on a large scale is demonstrated using direct current arc discharge with a rotating graphite anode in low pressure air. The process is time-saving, economical, and non-hazardous. It is found that the optimum air pressure for the highest yield of MWCNTs is about 60 Torr. Investigation of the internal organization of the cathode deposit reveals that many columns about 40 μm in diameter are closely packed and mechanically stable. The highest content of MWCNTs is found in the intercolumnar spaces between columns. Emitters made of the cathode deposits that contain a large number of straight nanotubes exhibit outstanding field emission properties. The turn-on electric field decreases from 1.44 to 0.93 V/μm and the field enhancement factor β increases from about 3,190 to 7,830 only after simple burning at 750 °C for 30 min in air. The results indicate that MWCNTs prepared by arc discharge in air are promising for field emission application.