Cuprous oxide films were prepared by the post-annealing of cupric oxide using an atmospheric pressure microwave plasma torch. Metallic copper films were deposited oil glass substrate by magnetron sputtering. Then the films were annealed in air at 500 degrees C for 12 h, and the formation of cupric oxide observed. The annealed Films were further treated by nitrogen plasma at a power of 800 W for 10 and 20 min. The color of the film clearly changed from black to reddish brown over 10 min. X-ray diffraction patterns show that the annealed films were cupric oxide and included cuprous oxide diffraction peaks observed after 10 min in nitrogen plasma. The resistivity of annealed Films was 16.7 Omega cm, and was reduced markedly to about one order of magnitude under nitrogen plasma. Annealing in air and nitrogen plasma treating shifted the optical band gap from 2.1 eV to 2.4 eV The relationship between the microstructure and plasma content of the films and their properties is investigated. (C) 2008 Elsevier B.V. All rights reserved.