Laser fabricated ripple substrates for surface-enhanced Raman scattering

Femtosecond laser fabricated surface nanograting structures, referred to as ripples, are proposed as efficient substrates for surface-enhanced Raman scattering (SERS). Ripple substrates show order of magnitude higher sensitivity and superior reproducibility as compared to lithographically made commercial SERS sensing substrates. It is demonstrated that the SERS intensity from ripple substrates scales with the thickness of the Au coating. Ag coating on sapphire ripples showed > 2000 times higher sensitivity as compared to the same coating on the flat sapphire surface. The period, duty cycle and aspect ratio of the ripple textures can be adjusted by laser ablation conditions, which could be used for plasmon resonance tuning.