Field emission from tetrahedral amorphous carbon films with various surface morphologies

Field emission properties of tetrahedral amorphous carbon films prepared by filtered cathodic vacuum arc technique have been compared with different surface morphologies. With fewer cycles of conditioning, field emission from relatively rough granular ta-C films on nickel-coated silicon substrates was routinely improved, due to a local field enhancement resulting from both a 'protrusion-on-protrusion' geometry and a relatively high sp(2) content in the film. A 2-MeV ion implantation machine was also employed to intentionally produce local graphitic channels in smooth ta-C films with a high fraction of sp(3) content on bare silicon. A relatively low threshold field was obtained from the ta-C film implanted at a dose of 10(12) cm(-2), which still remained an extremely smooth surface. However, for the highly graphitic sample implanted with a higher dose of over 4 X 10(13) cm(-2), no electron field emission was observed, even under a very high electric field of 40 V mum(-1). Therefore, a suitable sp(2) content in an sp(3) matrix, resulting in graphitic conductive channels in amorphous carbon films to produce a local field enhancement, may be the main factor in obtaining low threshold fields. Furthermore, protrusive structures could further increase the field enhancement factor, due to a 'protrusion-on-protrusion' geometry. (C) 2001 Elsevier Science B.V. All rights reserved.