Rapid Substrate Neutralization via Side-Chain Hydroxylated Copolymers for Efficient Vertical Alignment of Block...

Directed self-assembly (DSA) of block copolymers (BCPs) with a density-multiplication capability is a promising approach for next-generation nanolithography. However, achieving well-ordered, vertically oriented nanostructures remains challenging due to the stringent requirement for precise interfacial-energy balance between the BCP and the substrate. Here, we report a cost-effective and scalable substrate-neutralization strategy based on a random copolymer of polystyrene-r-poly(methyl methacrylate)-r-poly(2-hydroxyethyl methacrylate) (PS-r-PMMA-r-PHEMA). By tuning the feed ratio of HEMA, the hydroxyl density and surface energy of the copolymer can be controlled, thereby optimizing the wetting behavior of the PS-b-PMMA thin films. Critically, the side-chain hydroxyl groups in PS-r-PMMA-r-PHEMA formed multisite hydrogen bonds with SiO_x substrates, achieving interfacial equilibrium in 5 min, far faster than the 72 h required for conventional end-hydroxylated PS-r-PMMA-OH brushes. Moreover, we demonstrated the application of BCP films for the controlled coercivity of CoFe/SiO₂ films. This work provides a facile substrate-neutralization route, offering strong potential for large-scale nanolithography.