Plasma Fabrication and SERS Functionality of Gold Crowned Silicon Submicrometer Pillars.

Paola Pellacani,Franco Marabelli,Lucia Fornasari,Carlo Morasso,Miguel Manso Silvan,Silvia Picciolini,Dario Gallach

doi:10.3390/ma13051244

Abstract

Sequential plasma processes combined with specific lithographic methods allow for the fabrication of advanced material structures. In the present work, we used self-assembled colloidal monolayers as lithographic structures for the conformation of ordered Si submicrometer pillars by reactive ion etching. We explored different discharge conditions to optimize the Si pillar geometry. Selected structures were further decorated with gold by conventional sputtering, prior to colloidal monolayer lift-off. The resulting structures consist of a gold crown, that is, a cylindrical coating on the edge of the Si pillar and a cavity on top. We analysed the Au structures in terms of electronic properties by using X-ray absorption spectroscopy (XAS) prior to and after post-processing with thermal annealing at 300 °C and/or interaction with a gold etchant solution (KI). The angular dependent analysis of the plasmonic properties was studied with Fourier transformed UV-vis measurements. Certain conditions were selected to perform a surface enhanced Raman spectroscopy (SERS) evaluation of these platforms with two model dyes, prior to confirming the potential interest for a well-resolved analysis of filtered blood plasma.

Highlights

Surface engineering techniques are increasingly spanning into the field of optics, allowing the design of intricate material configurations with photonic [1], luminescent [2], photochemical [3], plasmonic [4], photovoltaic [5], or even dual [6] properties
The first screening of plasma parameters was performed in view of the special characteristics of the colloidal monolayer masks
The PS colloids were not dense but rather considerably soft and made contact to the surface only by an interfacial vortex, which limits their resistance to the plasma process and the derived thermal exposure

Summary

Introduction

Surface engineering techniques are increasingly spanning into the field of optics, allowing the design of intricate material configurations with photonic [1], luminescent [2], photochemical [3], plasmonic [4], photovoltaic [5], or even dual [6] properties. The relevance of the plasma processes for the surface engineering of optical structures stems from its versatility to work in deposition (additive process) or etching (removal process) conditions at a wide range of pressures, gas combinations, and temperatures, making the processing of organic and inorganic structures compatible. This versatility of operation in extremely different conditions, and flexibility for the processing of materials of different natures, is scarcely provided by pure ion, electron, or photon techniques.

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