Resistance of plasma-deposited a-C:H/fluorocarbon films to anodic breakdown in aqueous electrolytes

The corrosion characteristics of a-C:H/fluorocarbon composite films deposited on type 301 stainless steel substrates were investigated using potentiometry and electrochemical impedance spectroscopy. The films were deposited by radio frequency (13.56 MHz) plasma deposition from different mixtures of hexafluoroethane, acetylene, and argon. A 10 nm thick polysilicon film was plasma-deposited prior to a-C:H film deposition to improve adhesion. The anodic current densities recorded with all the coated samples, in an electrolyte consisting of 0.1 M NaCl and 0.1 M Na2SO4 at 1.5 V (Standard Calomel Electrode), were at least three orders of magnitude less than that for a bare steel sample. They were also at least 20 times less than that obtained with diamond-like carbon film-coated substrates, EIS spectra obtained for these samples, while exposed to 0.6 M NaCl solution over an extended period of time (30-40 days), confirm their barrier properties, All the coatings showed near capacitive behavior in the frequency range 10 mHz-4 KHz.