Adhesion Strength and Optical Transparency of DLC Coatings on Polycarbonate

Abstract

In this study, we investigated the adhesion strength and optical transparency of a-C, a-C:H, a-C:H:Si and SiO2 films deposited on polycarbonate. The a-C and SiO2 films were deposited by ECR-type ion beam sputtering system (ECR-type IBS), and the a-C:H and a-C:H:Si films were prepared with bipolar-type plasma based ion implantation (bipolar-type PBII). It is observed that the friction signal of the polycarbonate decreases due to the diamond-like carbon (DLC) coating, and the a-C:H:Si coating shows the lowest friction force. The a-C:H:Si film on the polycarbonate shows higher critical load, i.e., higher adhesion strength, compared to those of the a-C, a-C:H and SiO2 coatings. The transmittance increases due to the Si-addition to the a-C:H film in a wavelength range of 400 - 800 nm (visible range), whereas decreases in a wavelength range of 200 - 400 nm (UV range). The a-C:H:Si coating exhibits a larger optical band gap compared to those of other coatings due to highly sp3 dominant bonding structure. The a-C:H:Si is effective protective-coating for the polycarbonate due to its lower friction higher adhesion strength, higher transmittance in the VIS range and better UV protection ability compared to those of other coatings.