Hierarchical Order in Dewetted Block Copolymer Thin Films on Chemically Patterned Surfaces

Abstract

We investigated the dewetting process on flat and chemically patterned surfaces of ultrathin films (thickness between 2 and 15 nm) of a cylinder forming polystyrene- block-poly(methyl methacrylate) (PS- b-PMMA) spin coated on poly(styrene- r-methyl methacrylate) random copolymers (RCPs). When the PS- b-PMMA film dewets on a 2 nm-thick RCP layer, the ordering of the hexagonally packed PMMA cylinders in the dewetted structures extends over distances far exceeding the correlation length obtained in continuous block copolymer (BCP) films. As a result, micrometer-sized circular droplets featuring defectless single grains of self-assembled PS- b-PMMA with PMMA cylinders perpendicularly oriented with respect to the substrate are generated and randomly distributed on the substrate. Additionally, alignment of the droplets along micrometric lines was achieved by performing the dewetting process on large-scale chemically patterned stripes of 2 nm thick RCP films by laser lithography. By properly adjusting the periodicity of the chemical pattern, it was possible to tune and select the geometrical characteristics of the dewetted droplets in terms of maximum thickness, contact angle and diameter while maintaining the defectless single grain perpendicular cylinder morphology of the circular droplets.

Tailored and Guided Dewetting of Block Copolymer/Homopolymer Blends

“…After the thermal treatment, the formation of droplets periodically distributed within the prepatterned structures is observed (Figure b,c). As previously reported, the height of the droplets linearly scales with their diameter; thus, the maximum height reached by the droplet, shown in Figure c, is ∼95 nm.…”

“…In the case of BCPs treated at T a below the ODT, stable films not subjected to the rupture process are observed when h > 2· R g . In contrast, when h < 2· R g , dewetting processes occurs with ε ∼ 1. , This behavior suggested the occurrence of an additional stabilizing effect of the BCP nanometric morphology for h > 2· R g .…”

Aligned Morphologies in Near-Edge Regions of Block Copolymer Thin Films

“…McGraw et al studied the terracing of a lamellar BCP in a ring-shaped droplet of material . Lupi et al demonstrated the formation of single-grain hexagonal morphologies in ultrathin dewetted droplets of BCP cylinder-forming material . Printing methods have been applied to creating isolated patterns of BCP film material .…”

Hyperbolic Metamaterials via Hierarchical Block Copolymer Nanostructures

“…[ 29,45 ] At the same time, a reduced effective glass transition temperature imposed by the so‐called “wet brush” regime [ 29 ] significantly affects the thermal stability of the BCP film. As a result, a low‐temperature dewetting process, typically occurring in ultrathin (sub‐10 nm) films, [ 46 ] takes place on relatively thick BCPs. [ 36 ]…”