Both negative and positive substrate bias effects on structural and field-emissive properties of carbon nanombes (CNTs) are investigated. The CNTs are grown on Ni catalysts employing an inductively coupled plasma chemical vapor deposition (ICP-CVD) method by varying substrate bias from -550 to 400 V. Characterization using various techniques, such as field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Auger spectroscopy (AES), and Raman spectroscopy, shows that the physical dimension as well as the crystal quality of grown CNTs can be changed and controlled by the application of substrate bias during CNT growth. It is for the first time observed that the prevailing growth mechanism of CNTs which is either due to tip-driven growth or based-on-catalyst growth may be influenced by the application of substrate bias. It is also seen that negative bias would be more effectual for vertical-alignment of CNTs compared with positive bias, whereas the CNTs grown under positive bias display much better electron emission capabilities than those grown under negative bias or without bias. The reasons for all the measured data regarding the structural properties of CNTs are discussed to confirm the correlation with the observed field-emissive properties. (C) 2004 Published by Elsevier B.V.