Role of amorphous carbon nanowires in reducing the turn-on field of carbon films prepared by microwave-heated CVD

The effect of growth temperature (600-750 degreesC) and growth time on the field emission properties and microstructure of carbon thin films grown using microwave-heated CVD process and Ni as catalyst, was investigated. It was found that the 600 degreesC, 20 min grown and 650 degreesC, 10 min grown films consist of mixed carbon nanostructures: mainly amorphous carbon nanowires, and a few of hollow and 'bamboo-like' multi-walled carbon nanotubes. To the contrary, as the growth temperature was increased to 700-750 degreesC, long growth time of 20 min was needed and mainly multi-walled carbon nanotubes of high graphite quality were produced. Field emissions of the 700 and 750 degreesC grown carbon films show higher turn-on fields of 2.3-3.9 V/mum, as compared to the much lower turn-on fields of < 1 V/mum for the 600 and 650 degreesC grown carbon films. The improvement of emission characteristics in lower-temperature-grown films can be attributed to the larger field enhancement effect induced by the inhomogeneous electronic sp(2)/sp(3) structures and the hydrogen termination on amorphous carbon nanowires. (C) 2004 Elsevier B.V. All rights reserved.