The effect of bias voltage on the structural properties of amorphous carbon nitride films deposited by plasma decomposition of methane (CH4) and nitrogen (N-2) is investigated. A series of films was deposited under conditions in which diamond-like a-C:H films are obtained, i.e., bias of -200 V, and pressure of 1.0 Pa. Another series of films was deposited under conditions where graphite-like films are obtained, i.e., bias of -800 V, and pressure of 12 Pa. To investigate the effect of these conditions on the properties of the films, FTIR, Raman, nanohardness, and ESR measurements were undertaken. It was observed that the incorporation of nitrogen and the investigated properties depend on the base structure (diamond-like vs. graphite-like). (c) 2005 Elsevier B.V. All rights reserved.