Cu@Cu2O core-shell nanoparticles on the a-C: H thin films are prepared by co-deposition of RF-Sputtering and RF-PECVD. The samples with different Cu concentration and Cu nanoparticle with different size are grown. X-ray photoelectron spectroscopy (XPS) characterization indicates that the surface of the Cu nanoparticles oxidizes when they are exposed to air. The results are indicative that the shell of nanoparticle is mainly Cu2O phase with CuO cover thin layer. Surface plasmon resonance (SPR) peak that is signature of the existence of the Cu core nanoparticles appears in visible spectra of these films. Several interesting information are obtained from XPS study of these core-shells nanoparticles. The CuO/Cu2O ratio that is obtained by deconvolution of Cu 2p(3/2) main peak and from intensity ratio of the main and satellite peak of Cu 2p(3/2) are consistent. Background of XPS spectra is assigned to the scattering photoelectrons from Cu ions and plasmon of Cu nanoparticles. We observed that Cu core addition to copper oxide improves absorption of CO gas. (C) 2008 Elsevier B. V. All rights reserved.