Role of inorganic oxide interlayers in improving the adhesion of sputtered silver film on PMMA

Large mirrors are used to concentrate sunlight for renewable power generation. The reflector materials that are used must be inexpensive and maintain high specular reflectance for extended lifetimes in severe outdoor environments. Polymer reflectors are lighter than glass mirrors, offer greater system-design flexibility, and have the potential for lower cost. The state-of-the-art commercial reflector is a silvered polymethylmethacrylate (PMMA) polymer. Interlayer adhesion failure can limit the performance of the optical components used to convert solar energy into thermal or electric energy. Optically transparent, inorganic interlayers can improve adhesion in multilayer structures. We have evaluated interlayer adhesion in sandwich structures that are representative of solar mirrors and other devices. Experimental structures were fabricated by vacuum-sputtering thin layers onto substrates. The structures were evaluated for optical performance and for adhesion. Calculations show that the Lifshitz-van der Waals interaction does not account for the adhesion between silver and PMMA. Appropriate oxide interlayers improve the adhesion between silver and PMMA in conformity with the acid-base model for adhesion.