The electrical and optical properties of diamondlike carbon films deposited by direct current magnetron sputtering on Si substrates at room temperature have been measured as a function of the ion energy (E-ion) and ion-to-carbon flux (J(ion)/J(C)) . The results show that, in the ranges of 5 eV less than or equal to E(ion)less than or equal to85 eV and 1.1less than or equal toJ(ion)/J(C)less than or equal to6.8, the presence of defective graphite formed by subplanted C and Ar atoms, voids, and the surface roughness, are the dominant influences on the resistivity and optical absorption. (C) 2003 American Vacuum Society.