Cobalt-containing amorphous carbon (a-C:Co) composite films have been prepared by filtered cathodic vacuum arc at high negative pulsed bias voltage. After heat treatment at 580 degreesC in a mixture of acetylene and hydrogen gases, field emission properties of the a-C:Co films were significantly improved and the films deposited at higher negative bias voltage possessed better field emission properties. A relatively low threshold field of 2.1 V/mum (for emission current I muA/cm(2)) and a high emission current density of 2 mA/cm(2) at the electric field of 6 V/mum has been achieved for the films deposited at the negative bias voltage of 7 W The morphologies and structures of the a-C:Co films were also studied in detail. It is suggested that the employed negative bias voltage increases the grain size and the sp(2) content in the films, and further improves the field emission properties. (C) 2003 Elsevier Science B.V. All rights reserved.