Corrugated thin metal films as couplers between propagating and surface modes for plasmonic enhancement of photocatalytic optofluidic microreactors

Abstract

Surface plasmons polaritons (SPP) ensure extreme concentrations of electromagnetic near fields at interfaces between materials with negative and positive dielectric permittivity (i.e. between metals and dielectrics), usually several orders of magnitude compared to fields in free space. This is useful for a number of practical applications, including chemical and biological sensing, enhancement of photodetectors and improvement of photocatalytical reactions. One of the problems to be solved with plasmonic field localization is that wavevectors of SPPs may vastly exceed those of propagating waves, so that a coupling device is mandatory between them. In photocatalytic microreactors one often uses nanoparticles with localized SPP as both couplers and field enhancers. In this contribution we consider the possibility to utilize surface corrugation of thin gold films to simultaneously ensure coupling between propagating and plasmon modes and enlarge effective catalytic surface. To this purpose we utilize wet chemical etching (chemical micromachining). Different surface corrugations are obtained by varying etching conditions. A combination of gold thin film over corrugated surface and titanium dioxide nanoparticles is used. The setup can be used for different photocatalytic processes.