Effects of consecutive processing between cleaning and deposition on adhesion of diamond-like carbon prepared by plasma-based ion implantation and deposition

The effects of pretreatment on adhesion, which is the most important challenge of diamond-like carbon (DLC) films, were investigated. DLC films were prepared by changing pretreatment conditions on austenitic stainless steel (SUS304) substrates by hybrid process of plasma-based ion implantation and deposition (PBIID) using superimposed RF and negative high-voltage pulses. Although an oxide layer on a substrate surface was removed by Ar-plasma sputter cleaning, the substrate surface was immediately reoxidized when plasma was stopped for a moment between sputter cleaning and deposition. The DLC film on the oxide layer was poor adhesion strength less than approximately 50 MPa. Even if the oxide layer existed on the substrate surface, carbon ion implantation as an interface treatment in the PBIID process broke the oxide layer. As a result, the adhesion strength of DLC films was enhanced above the strength of epoxy resin (about 70 MPa). Furthermore, it was found that continuous generation of plasma after sputter cleaning was able to suppress reoxidation of the substrate surface. Consequently, the adhesion strength of DLC films prepared with no interface treatment was increased above 70 MPa, suggesting simplification of coating process and reduction in processing time for cost reduction.