2.2.2. BCP Self-Assembly Process

The surface of silicon oxide wafer was chemically modified by a PS-r-PMMA random copolymer brush to provide identical interfacial tensions for the PS and PMMA blocks [33,34]. The PS-r-PMMA brush layer (thickness ~40 nm) was deposited by spin-coating process (1 wt% in toluene, 1000 rpm, 60 s) and subsequent thermally annealed at 160 °C for 48 hrs in a vacuum chamber (Figure 1b) [35]. Then, the un-grafted random brush layer was removed by sonication in toluene for 15 min by 3 times. After surface modification, a symmetric diblock copolymer, PS-b-PMMA thin film (thickness ~120 nm) was spin-casted (2 wt% in toluene, 1600 rpm, 60 s). Afterwards, thermal annealing was conducted at 220 °C for 48 hrs in a vacuum chamber to produce the surface perpendicular BCP nanodomain (Figure 1c).