Gold coating of a plastic optical fiber based on PMMA

Abstract

We investigated the adhesion between gold thin film and poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)) substrates with the aim of imparting electrical conductivity to plastic optical fibers (POFs). The two polymers were used as the core and the cladding of POF, respectively. Gold thin film of 50nm thickness was deposited by ion sputtering onto the polymers and also POF. Several approaches, which were well known to be effective in enhancing adhesive strength between gold and polymers, were applied in this study: introduction of polar functionality on the substrate surface by plasma treatment, buffer layer insertion, and physical surface roughening. The variation of wettability and adhesion with plasma conditions was investigated through water contact angle measurement and cross hatch cut test. Even though the contact angles of substrates were decreased after Ar or O2 plasma treatment, irrespective of the polymer type, the adhesion of polymers with gold layer was very poor. The Ti buffer layer of 5nm thickness, which was deposited between PMMA substrate and gold layer, did not contribute to improve the adhesion. However, P(VDF-co-HFP) substrates with rough surface of 13.44nm RMS shows 3B class adhesion to gold from the cross hatch tape test. The gold-coated POF showed the electrical conductivity of 1.35×103Scm-∈1 without significant optical loss. The result may be used for developing a medical device capable of simultaneously applying electrical and optical stimulus. © 2009 Springer Berlin Heidelberg.