Plasma density induced formation of nanocrystals in physical vapor deposited carbon films

The effect of plasma parameters on the nanostructures formed during physical vapor deposition growth of carbon films has been studied. It was shown that the formation and nature of nanostructures strongly depend on plasma density and ion energy during the deposition. High plasma density results in formation of nanocrystals with preferred orientation even at low negative substrate bias (300 V) while at low plasma density higher substrate bias (500 V) is required for the nanocrystals. Moreover, at the same plasma density the nature of the nanostructures strongly depends on the ion energy. At higher ion energies, carbon nanotubes are formed in the microstructure while at lower ion energies, graphitic nanostructures are more stable. It was also found that prior to the formation of preferred orientation, an amorphous layer is formed at the silicon/carbon interface. Through electron energy loss spectroscopy, it is shown that the structure of this layer strongly depends on ion energy during the deposition. (C) 2011 Elsevier Ltd. All rights reserved.