Determination of Pinhole Defects in Diamond-like Carbon Film by Electrochemical Test with CPCD Method

摘要

Diamond-like carbon (DLC) films were coated on SUS3O4 stainless steel using an ionization deposition method, and the area of defects in the films was determined by the critical passivation current density (CPCD) method. The area of pinhole defects in the DLC films (R_i) was evaluated as a function of applied negative bias voltage and film thickness. The value of R_i was not influenced by the bias voltage for films thinner than 100 nm, but decreased with increasing bias voltage for films thicker than 100 nm. For each bias voltage, the density and size of the defects in the DLC films decreased with increasing thickness. In particular, the Ri-value of the 550 nm film prepared at the bias voltage of -2000 V was approximately 0.01 percent, less by a factor of 100 than that of TiN films of similar thickness prepared by the hollow cathode discharge technique. On the basis of these findings it is concluded that protective ability is remarkably improved by DLC films (thinner than 600 nm) prepared by ionization deposition.