Laser fabrication of periodic arrays of microsquares on silicon for SERS application

Abstract

Two dimensional periodic arrays of microsquares of different dimensions are fabricated by direct ns-laser writing on silicon substrate. The micro/nano structures pattern on the Si surface significantly minimizes the optical reflection by light trapping effect, but enhances the SERS signal intensity of analyte dye molecule Rhodamine B (RhB) and Methylene Blue (MB) in presence of gold nanoparticles. The dependence of surface roughness, optical reflection and SERS intensity on the laser pulse energy and line scan interval is investigated. The SEM images clearly show well-ordered features on the surface of patterned Si substrates and aggregation of micro/nanoparticles on the substrate surface. The optical reflection from the patterned surfaces reduces below 11% over a broad range of wavelengths from 300nm to 1200nm. The patterned surface can be used as a reproducible SERS substrate with a spatially uniform enhancement factor of 108. This fabrication method can be employed for preparation of multifunctional surfaces for light trapping in solar cells and for Raman signal amplification for versatile and reproducible SERS sensors.