Block Copolymer Films with Free Interfaces: Ordering by Nano-Patterned Substrates

TL;DR

This study explores how free interfaces in block copolymer films on nano-patterned substrates influence their self-assembly and morphology, revealing complex domain arrangements and interface shapes relevant for nanofabrication techniques.

Contribution

It introduces a self-consistent model for BCP films with free interfaces on patterned substrates, highlighting the impact on domain orientation and morphology.

Findings

Free interfaces induce mixed parallel and perpendicular domains.

The free interface relaxes boundary constraints, altering BCP ordering.

Results have implications for nanolithography and patterning techniques.

Abstract

We study block copolymers (BCP) on patterned substrates, where the top polymer film surface is not constrained but is a free interface that adapts its shape self-consistently. In particular, we investigate the combined effect of the free interface undulations with the wetting of the BCP film as induced by nano-patterned substrates. For a finite volume of BCP material, we find equilibrium droplets composed of coexisting perpendicular and parallel lamellar domains. The self-assembly of BCP on topographic patterned substrates was also investigated and it was found that the free interface induces mixed morphologies of parallel and perpendicular domains coupled with a non-flat free interface. In both cases, the free interface relaxes the strong constraints that would otherwise be imposed by a fixed top boundary (which is commonly used in simulations), and affects strongly the BCP ordering. Our study has some interesting consequences for experimental setups of graphoepitaxy and nanoimprint lithography.