EIS capacitance diagnosis of nanoporosity effect on the corrosion protection of DLC films

An electrochemical impedance spectroscopy (EIS) capacitance diagnostic method was developed to measure the nanoporosity in DC magnetron-sputtered diamond-like carbon (DLC) films deposited on highly conductive silicon (111) substrates. The measurement was based on a calibration of artificial defects enclosed in a well-defined area. Films of known nanoporosity, as determined by EIS, were used to study the effect of nanopores on the corrosion protection behavior of DLC films in sulfuric acid. EIS was also used to determine the corrosion protection behavior of the film as a function of immersion time in 0.5 M H2SO4 solution. The polarization behavior of the film in sulfuric acid was studied with a potentiodynamic polarization. The corroded film surface was then examined with atomic force microscopy (AFM). The impedance behavior of the film with nanoporosity is capacitive. and the EIS method is sensitive for the detection of nanopores in DLC films and reliable in evaluation of the Porosity level. The porosity density in the film. increases with immersion time, and the nanopores can cause localized corrosion of the substrate. This study has confirmed that the corrosion resistance of DLC films, was compromised to a large extent by the nanopores in the films. (C) 2002 Elsevier Science B.V. All rights reserved.