Perpendicular SiO2 cylinders fabricated from a self-assembled block copolymer as an adaptable platform

Abstract

We discuss the formation of perpendicular cylinders from polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS), which were used to fabricate silica (SiO2) pillar arrays with an aspect ratio of 5. The solvent used in spin-coating solutions to form the initial films played an important role to lead the final morphology of the cylinders after solvent annealing. Tetrahydrofuran, a selective solvent for the major PS block, trapped PDMS spheres in isolation, opening a route to form highly aligned perpendicular cylinders after an induction period. Meanwhile, cyclohexane, a non-selective solvent, connected PDMS domains to some extent and provided a different route through which moderate regularity was achieved with gradual improvement. The transient morphological changes of the cylinders were precisely investigated using grazing-incidence small-angle X-ray scattering and scanning electron microscopy. The alignment of the final morphology of the cylinders was validated by reflectance and optical ellipsometry measurements. Oxygen plasma was used to completely remove organic substances and convert PDMS to SiO2, providing a platform suitable for various applications. As an example, a surface-enhanced Raman spectroscopy (SERS) platform was obtained by depositing gold on a perpendicular silica array. This platform exhibited substantial SERS enhancement using Rhodamine 6G as a probe molecule. Identical enhancements were observed throughout the platform, which was attributed to its uniform nanostructures.