The improvement in gas barrier performance and optical transparency of DLC-coated polymer by silicon incorporation

Abstract

In this study, induced modification caused by silicon incorporation (up to 21 at.%) in the composition and microstructure of hydrogenated amorphous carbon (a-C:H) thin films synthesized by plasma-enhanced chemical vapour deposition (PECVD) technique has been studied. The effect of this new microstructure on gas barrier performance and optical properties has been studied. A small amount of silicon incorporation (8.5 at.%) into the a-C:H coatings significantly improves the barrier performance, giving a gas reduction factor of 98%. Moreover, silicon incorporation results in an enhancement of optical band gap (doubled its value) and in a reduction of film density, stress, and refractive index. The silicon inclusion in the a-C:H structure breaks down large size sp 2 carbon clusters and enhances the sp 3 bonding; however, the use of tetramethylsilane (TMS) precursor gas in the PECVD process also leads to the development of a more polymer-like structure due to the increasing hydrogen content. The development of sp 3 bonding and the reduction of large sp 2 graphitic clusters are responsible for the enhancement of the optical band gap. We have demonstrated that Si- a-C:H thin film coatings can be used as a transparent barrier coating on polymer substrates with barrier performance comparable to that of conventional metal oxides coatings.