Perpendicular Orientation of PS-b-PMMA Microdomains Controlled by the Grafting Density of P(S-r-MMA) Brushes

Perpendicularly-oriented microdomains of diblock copolymer (di-BCP) was studied by means of fine-tuning the grafting density (σ) of random copolymer brushes, which balances the interfacial interactions between substrate and each block of BCP. In this study, a ‘grafting-to’ approach with end-functionalized random copolymer was applied to modify the silicon substrate and the thickness window for perpendicular orientation of lamella-forming di-BCP was observed in both ways of simulation and experiment. Moreover, we identified the minimal value of grafting density to achieve the largest thickness window, quantified by the radius of gyration of random copolymer chain (σR_g²). The result provides a guide for the appropriate extent of surface modification by random copolymer, which leads to photolithography or nanoimprinting application of self-assembled BCP thin film.