The effect of nitrogen partial pressure on the bonding in sputtered CNx films: implications for formation of beta-C3N4

An investigation of the bonding structure in carbon nitride films deposited by DC magnetron sputtering using a Penning-type opposed target system has been carried out. The changes in the valence band structure have been measu red by XPS, UPS and EELS. The density of unpaired electrons has been measur ed by ESR. As the nitrogen partial pressure and the nitrogen content of the films is initially increased, the structure shows a greater degree of sp(2 ) bonding compared to the pure carbon samples. However, with further increa ses in the nitrogen partial pressure up to 100% of the sputtering gas press ure, which has very little effect on the nitrogen content of the films, the bonding becomes more sp(3)-like in character and there is evidence for a r eduction in the network terminating C=N bonding. Under these circumstances the sp3-like nature becomes comparable to or greater than that for un-nitro genated films. These results point to the reasons why crystalline beta -C3N 4 material has been found in these films only with high nitrogen partial pr essure even though the nitrogen content is not significantly enhanced in th is situation. (C) 2000 Elsevier Science B.V. All rights reserved.