*2.2. DLC Coating Procedure*

DLC films were deposited onto stainless steel disks and wires using a plasma-based ion implantation/deposition (PBIID) method after the specimens were cleaned ultrasonically with acetone and alcohol. A custom-made jig was used to hold the specimens in the PBIID equipment (PEKURIS-HI; Kurita Seisakusho, Kyoto, Japan). To obtain DLC films with different compositions, two different parameters for target voltage, gas atmosphere and deposition time were used; these are listed in Table 1. All deposition processes were carried out at a pressure of 1.33 × <sup>10</sup>−<sup>3</sup> Pa.


**Table 1.** Deposition parameters for the DLC coating procedure used in the present study.
