Plasma-induced stabilization of pmma surfaces for enhanced adhesion of plasma-deposited coatings

Adhesion of plasma-deposited optical and protective coatings, such as amorphous hydrogenated silicon nitride, SiN1.3, on polymethyl-methacrylate (PMMA) substrates has been found to be limited by a cohesive failure inside the PMMA bulk. Using direct exposure to a low pressure plasma in helium or to vacuum ultraviolet radiation generated from H-2 plasma for an extended period of time, we succeeded to obtain excellent adhesion even under a humidity test at elevated temperature. We found, using a multitechnique approach, that such improved adhesion is achieved by forming a crosslinked, mechanically stabilized layer in the interfacial region, which possesses a physical thickness of 50 to 100 nm.