The corrosion characteristics of diamond-like carbon (DLC) films, deposited on aluminum film-covered single-crystal silicon substrates were investigated using standard potentiometric methods. The DLC films were deposited by radio frequency (13.56 MHZ) plasma deposition from three different precursors, methane, acetylene, and 1,3 butadiene, with argon or hydrogen as the diluent. A 5 nm thick polysilicon (PS) film was plasma-deposited prior to DLC film deposition to improve adhesion. The measured corrosion current increased with an increase in the hydrogen content in the feed gas mixture and was lowest for the films deposited from butadiene and highest for those deposited from methane. Also, the DLC films deposited at higher gas flow rates and lower rf powers offered better protection against corrosion than those deposited at lower gas flow rates and higher rf powers. Annealing improved the corrosion resistance. The corrosion currents for certain DLC/PS/Al/Si samples were about 15 times smaller than those for polyimide (PI)/Al/Si samples.
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.
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