Perpendicular Structure Formation of Block Copolymer Thin Films during Thermal Solvent Vapor Annealing: Solvent and Thickness Effects.

Qiuyan Yang,Katja Loos

doi:10.3390/polym9100525

Abstract

Solvent vapor annealing of block copolymer (BCP) thin films can produce a range of interesting morphologies, especially when the perpendicular orientation of micro-domains with respect to the substrate plays a role. This, for instance, allows BCP thin films to serve as useful templates for nanolithography and hybrid materials preparation. However, precise control of the arising morphologies is essential, but in most cases difficult to achieve. In this work, we investigated the solvent and thickness effects on the morphology of poly(styrene-b-2 vinyl pyridine) (PS-b-P2VP) thin films with a film thickness range from 0.4 L0 up to 0.8 L0. Ordered perpendicular structures were achieved. One of the main merits of our work is that the phase behavior of the ultra-high molecular weight BCP thin films, which hold a 100-nm sized domain distance, can be easily monitored via current available techniques, such as scanning electron microscope (SEM), atomic force microscope (AFM), and transmission electron microscope (TEM). Systematic monitoring of the self-assembly behavior during solvent vapor annealing can thus provide an experimental guideline for the optimization of processing conditions of related BCP films systems.

Highlights

The self-assembly of block copolymer (BCP) thin films can generate structures with a tailored length, enabling them to be desirable templates for nano-manufacturing [1]
This process is highly effective over comparatively short timescales, for high molecular weight BCPs in comparison to thermal annealing, due to the dramatic enhancements of chain mobility afforded by the presence of a plasticizing solvent in the BCP film as compared to the thermal-activation of chain motion in a dry melt [1]
Contributed by its high χN (≥100) value, a lamellar spacing (L0 ) around 146 nm is observed in the transmission electron microscope (TEM) image of an annealed BCP sample with a thickness higher than 45 L0 (Figure 1)

Summary

Introduction

The self-assembly of block copolymer (BCP) thin films can generate structures with a tailored length, enabling them to be desirable templates for nano-manufacturing [1]. In SVA, as-prepared block polymer thin films are exposed to vapors of one or more solvents at temperatures typically well below the bulk Tg of both blocks to form a swollen and mobile polymer film on the substrate [4] This process is highly effective over comparatively short timescales, for high molecular weight BCPs in comparison to thermal annealing, due to the dramatic enhancements of chain mobility afforded by the presence of a plasticizing solvent in the BCP film as compared to the thermal-activation of chain motion in a dry melt [1]. Various arrays including micellar, laminar, and cylindrical domains of PS-b-P4VP with a high degree of orders were produced by Park and Russell, which were further used as the templates for the fabrication of porous films [5], dot and stripe arrays [6,7], metallic line patterns [8], and ordered structure designs [9,10,11]

Methods

Results

Conclusion