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

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. (c) 2004 Elsevier B.V. All rights reserved.