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 tempera ture of 20 degrees C by pulsed laser deposition using a graphite target. Th e laser source used was an ArF excimer laser. The ambient pressure was vari ed between 10(-7) and 1 Torr by adjusting the gas flow of hydrogen or oxyge n. 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 typi cal diamond-like carbon films prepared using other methods. The absorption coefficients decreased and the optical band gaps increased at pressures hig her than 10 mTorr for hydrogen and 0.1 mTorr for oxygen. These results indi cate that both hydrogen and oxygen are effective in etching an sp(2) bondin g fraction. The sp2 etching processes for ambient hydrogen and oxygen could be explained well by the combination of the expected ablation processes an d the reaction rate between carbon atoms and the ambient gases. (C) 2000 El sevier Science S.A. All rights reserved.