Phase separation induced controllable nanoscale roughness in PS-b-PMMA Di-block copolymer thin films for enhanced anti-reflectivity

This study demonstrates a simple method to control surface roughness and, consequently, the optical properties of PS-b-PMMA thin films. By utilizing different solvent combinations and post-treatment steps, we can precisely tune the surface morphology, leading to significant variations in the films' reflectance and transmittance characteristics. As-fabricated rough and porous PS-b-PMMA thin films exhibited omnidirectional broadband anti-reflective behaviour, with surface roughness values ranging from similar to 25 nm to 300 nm. Reflectance measurements showed near-zero reflection (as low as 0.045%) for PS-b-PMMA thin films, and transmittance was minimized to 0.7%. This work uniquely demonstrates the ability to tune surface roughness over more than one order of magnitude, from nano to sub-micron scale, using a straightforward and scalable method. The significant reduction in reflectance and transmittance achieved in this study underscores the potential application of these films in optoelectronic devices, marking a notable advancement over existing techniques.