Chromium oxynitride Cr-N-O thin films have been prepared by pulsed laser deposition. The thin films were formed by depositing chromium metal vapor in nitrogen or ammonia ambient gas with residual oxygen. Comparing the data obtained for thin films deposited in both ambient gas by using Rutherford backscattering spectroscopy, it was found that the thin films contained similar to 3 to 43 at.% oxygen. X-ray diffraction results indicated that the crystallographic structure of the main phase in the thin films was of the B I (NaCl) type when the oxygen content of the thin film was below 37 at.%. The results indicated that thin films with a Cr(N-x,O-y) phase with varying oxygen content, which has a non-metal substituted CrN structure, was successfully produced. The hardness of the Cr(N-x,O-y) thin films showed a maximum value for an oxygen concentration of 37 at.% oxygen, which was the maximum concentration of oxygen incorporated in the B1-NaCl structure Cr(N,O). Oxygen atoms dissolved in the B1 structure likely enhanced the hardness of the thin films. (c) 2006 Elsevier B.V. All rights reserved.