The role of hydrogen and oxygen gas in the growth of carbon thin films by pulsed laser deposition

Carbon thin films of thickness 100 nm were deposited at a substrate temperature of 20 degrees C by pulsed laser deposition using a graphite target. The laser source used was an ArF excimer laser. The ambient pressure was varied between 10(-7) and 1 Torr by adjusting the gas flow of hydrogen or oxygen. Raman spectrum measurement showed a broad peak with a center at 1550 cm(-1) for all films deposited in both ambient gases, similar to those of typical diamond-like carbon films prepared using other methods. The absorption coefficients decreased and the optical band gaps increased at pressures higher than 10 mTorr for hydrogen and 0.1 mTorr for oxygen. These results indicate that both hydrogen and oxygen are effective in etching an sp(2) bonding fraction. The sp2 etching processes for ambient hydrogen and oxygen could be explained well by the combination of the expected ablation processes and the reaction rate between carbon atoms and the ambient gases. (C) 2000 Elsevier Science S.A. All rights reserved.