Gold nanoisland arrays by repeated deposition and post-deposition annealing for surface-enhanced Raman spectroscopy.

Gold nanoisland arrays with well controlled growth were achieved by repeated sputtering deposition and post-deposition annealing processes. When each deposition was set at 5 nm (nominal thickness based on gold mass), the single deposition and annealing process (single process) yielded gold nanoisland arrays with an average diameter of ~16 nm based on top view scanning electron microscopy (SEM). When the deposition and annealing process was repeated two more times (triple process), top view SEM showed the nanoisland arrays grew to ~38 nm in average diameter. The surface-enhanced Raman spectroscopy (SERS) measurement indicated that triple processed nanoisland arrays led to the highest SERS enhancement, suggesting the necessity of pursuing nanoislands with larger sizes. The gold nanoisland arrays after the triple process were further sputtered with a final layer of gold thin film at different nominal thicknesses. An optimal nominal thickness for SERS was determined experimentally at ~40 nm, as a result of the competition between the positive and negative effects of the final gold deposition. Last, the uniformity of the optimized SERS substrate was investigated on a 5 cm x 5 cm platform. SERS measurements demonstrated a relative standard deviation of ~7% in terms of spectral variation over the entire substrate, rendering the process in the present study a promising fabrication approach for large-scale production of SERS substrates.