Field emission from bamboo-like multiwalled carbon nanotube arrays enhanced by mild oxidation

Multiwalled carbon nanotube (MWNT) arrays prepared by pyrolysis of Ni-phthalocyanine are heated at mild temperatures (100-300degreesC) in air. The arrays oxidized at 150degreesC exhibit the most excellent field emission characteristics, such as a turn-on voltage of 180 V and a current density of 10 mA.cm(-2) at 300 V. It is clarified by high-resolution electron microscopy of the MWNT that the MWNT tip is sharpened by selective oxidation at 150degreesC without affecting the graphytic cell structure. The lowest turn-on voltage is still higher than the voltage evaluated in a single metallic emitter with an identical radius. The reason for this discrepancy is discussed.