WiFi-like Nanostructures from Confinement of Block Copolymer Microdomains in Asymmetric Hemisphere Nanocavity

Abstract

We investigated the morphology of lamellae-forming polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) confined in asymmetric hemisphere nanocavities which were prepared by oblique angle deposition of gold with various thicknesses. When the thickness of the deposited gold layer (tAu) was 0.5L0 of PS-b-PMMA (L0 is the lamellar domain spacing of PS-b-PMMA in bulk), concentric lamellar patterns were formed on the top surface of the nanocavities. Interestingly, at tAu = 1L0, WiFi-like nanopatterns were observed on the top surface. This is because of the reduction of dislocations of PS and PMMA lamellar microdomains near the center of the nanocavity. The experimentally observed morphologies are consistent with prediction by self-consistent field theory. In addition, the inner wall of the hemispherical nanocavity was modified by grafting three different polymer brushes (PS, PMMA, and PS-r-PMMA) to change the affinity to each block. When the nanocavity was grafted by PMMA, WiFi-like nanopatterns were observed. On the other hand, laterally stacked U-shaped nanopatterns were formed in a nanocavity grafted by PS-r-PMMA with neutral affinity to PS and PMMA. We also fabricated an array of silver WiFi-like nanopatterns composed of laterally stacked split-ring resonators after selective silver deposition only on the PS microdomains. They showed unique plasmonic resonances depending on the polarization angle of incident light in near-infrared (NIR) wavelengths. The nanopatterns with broken symmetry obtained in this study can be used in advanced optical devices for structural coloration and optical anticounterfeiting.