Block Copolymer at Nano-Patterned Surfaces

TL;DR

This paper uses numerical self-consistent field theory to study how patterned surfaces influence the orientation of lamellar phases in symmetric block copolymer films, revealing conditions for perpendicular alignment.

Contribution

It introduces a detailed numerical analysis of block copolymer lamellae on patterned surfaces, highlighting how surface design affects phase orientation and metastability.

Findings

Chemical stripes induce perpendicular lamellae but can cause metastable mixed states.

Grooved molds reliably produce perfect perpendicular lamellae.

System sensitivity to initial conditions influences phase outcomes.

Abstract

We present numerical calculations of lamellar phases of block copolymers at patterned surfaces. We model symmetric di-block copolymer films forming lamellar phases and the effect of geometrical and chemical surface patterning on the alignment and orientation of lamellar phases. The calculations are done within self-consistent field theory (SCFT), where the semi-implicit relaxation scheme is used to solve the diffusion equation. Two specific set-ups, motivated by recent experiments, are investigated. In the first, the film is placed on top of a surface imprinted with long chemical stripes. The stripes interact more favorably with one of the two blocks and induce a perpendicular orientation in a large range of system parameters. However, the system is found to be sensitive to its initial conditions, and sometimes gets trapped into a metastable mixed state composed of domains in parallel and perpendicular orientations. In a second set-up, we study the film structure and orientation when it is pressed against a hard grooved mold. The mold surface prefers one of the two components and this set-up is found to be superior for inducing a perfect perpendicular lamellar orientation for a wide range of system parameters.