Amorphous carbon nitride (a-C1-xNx) films were prepared by magnetron sputtering using nitrogen (N-2) and oxygen (O-2) gases in order to reduce the sp(2) structural region and to reduce triple bonding between carbon and nitrogen atoms (C=N) with oxygen radical. Furthermore, these films were prepared at liquid-nitrogen temperature in order to increase the nitrogen concentration. Electron spin resonance (ESR), infrared (IR) absorption, ultra violet visual (UV-vis) spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to investigate the effects of O-2 gas addition and substrate cooling on the preparation of a-C1-xNx films by magnetron sputtering.