Femtosecond laser-nanostructured substrates for single molecule surface-enhanced Raman spectroscopy

We present a new type of surface-enhanced Raman scattering (SERS) substrate that exhibits extremely large and uniform cross-section enhancements over a macroscopic (>25mm2) area. The substrates are fabricated using an extremely simple procedure: a train of femtosecond laser pulses is used to structure a silicon wafer with an array of submicron-sized spikes, and a silver film is subsequently deposited on the structured surface. SERS signals from adsorbed molecular dyes indicate a spatially uniform enhancement factor (ca. 10^7) that is consistently observed over a wide range of excitation wavelengths. We present evidence of single molecule SERS performed using these substrates.