Amorphous carbon nitride (a-C:N) films were deposited by reactive direct current magnetron sputtering of graphite using a gaseous mixture of Ar and N-2. X-ray photo electron spectroscopy analysis (XPS) showed that there is an optimum volume ratio of nitrogen:argon in the sputter gas that results in a maximum content of incorporated nitrogen in the films. By using different take-off angles in XPS experiments, the variation gradient of bonding structure near the surface of a-C:N films has also been studied. In the surface layer of the a-C:N films, it was found that some of the initially formed beta-C3N4-like phase transforms to a graphite-like carbon-nitrogen phase. This structural change is driven by the nitrogen in the sputter gas during deposition.