Generation of scalable quasi-3D metallo-dielectric SERS substrates through orthogonal reactive ion etching

Abstract

We combined two orthogonal reactive ion etching strategies on monolayers of 4 μm diameter polystyrene (PS) microspheres assembled on a planar glass substrate to create geometrically diverse but highly regular quasi-3D nano-structured arrays with centimeter length scales. Reactive ion etching (RIE) with O₂/CF₄ was used to selectively etch PS and, thus, to adjust the morphology of the PS mask, and CHF₃ RIE was then used to etch the SiO₂ substrate. The dynamic combination of these two etching procedures facilitated the realization of a wide variety of 3D-corrugated surface morphologies, including pedestals, bowls, honeycombs and blossom bud like arrays. The generated structures were then evaporated with Au films of defined thicknesses to generate metallo-dielectric arrays with tunable surface roughness. Hexagonal diffraction patterns from the fabricated structures confirm the successful realization of extended periodic hexagonal structures and the optical transmission spectra showed an efficient trapping of incident light in these ultra-rough metallo-dielectric arrays. The metallo-dielectric substrates were finally optimized for the detection of the pesticide methyl parathion in a concentration as low as 1 × 10⁻¹⁰ M through surface enhanced Raman spectroscopy (SERS).