Nano-texturing of Transparent Polymers with Plasma Etching: Tailoring Topography for a Low Reflectivity

The reflectivity of transparent polymers can be reduced with a proper nanotextured layer on the surface according to the moth eye effect. Plasma etching has been proved to be a reliable method to generate self-organized nanostructures on the surface of various polymers. In the present work this method, directly carried out in one step, has been tested on polycarbonate for application as low reflective transparent material. CF4 and O2 fed plasma processes have been compared at different treatment time. Chemical (X-ray photoelectron spectroscopy), morphological (scanning electron microscopy), and optical (diffuse and specular reflectance, normal and grazing incidence) features have been evaluated. Results indicate that the CF4-to-O2 feed ratio significantly affects shape and distribution of the generated structures. O2 plasma, in particular, leads to taller structures with wire-like aspect and more homogeneous distribution, which are more effective in reducing reflectance with a broadband character (visible and near-infrared). Treatment duration, which instead affect mainly the dimension scale of the structures, must be tailored in order to control diffuse component of reflectance.