Electronic structure of hydrogenated carbon nitride films

Hydrogen-induced changes on the electronic and structural properties of amorphous carbon nitride (a-CNx:H) prepared by ion beam assisted deposition are investigated by x-ray photoelectron, ultraviolet photoelectron, infrared, and Raman spectroscopies. Two series of specimen are studied: films with a constant nitrogen content (C/N = 26%) grown at 150 degrees C using different hydrogen partial pressures between 0% and 70% and samples deposited at different substrate temperatures (150-500 degrees C) with fixed Hz partial pressure of 60%. The pronounced changes of the N 1s and C 1s core level spectra on increasing hydrogen incorporation (up to 17 at. %) are interpreted as due to the formation of terminating NH and CH bonds accompanied by modifications of the local C-N bonding structure. Corresponding changes are observed in the He II valence band spectra showing a recession of the leading edge of more than 0.9 eV while the optical band gap widens from 0 to more than 1 eV. Consistent with these results, the information obtained from the infrared and Raman spectra suggests a hydrogen induced transformation of the disordered sp(2)/sp(3) network into a polymerlike structure. With increasing substrate temperature a reversed process takes place. At 700 degrees C an increasing graphitization of the films is observed, but the effect of hydrogen on the structure influencing the growth kinetics is still present at this temperature. The nitrogen concentration (N/C) of about 30% indicates high thermal stability of the CN material. (C) 1998 American Vacuum Society. [S0734-2101(98)05705-4].