X-Ray reflectivity is used to determine the electron density profiles normal to the surface of diamond-like carbon DLC films Ž . prepared by plasma-enhanced chemical vapor deposition PE-CVD . Average values of the scattering lengths obtained from the Ž . specular reflection data and elastic recoil detection analysis ERDA hydrogen measurements are used to calculate the average mass density of the films. The density is shown to be strongly dependent on the hydrogen content. This depends on the plasma parameters. Argon diluted methane plasma produces homogeneous DLC films but generally with a lower density than the films prepared from pure or He diluted plasmas. These later plasmas produce films with a high density contrast and higher densities.
