Gold-coated zinc oxide nanowire-based substrate for surface-enhanced Raman spectroscopy

Zinc oxide nanowires with two distinct morphologies were synthesized on silicon substrates using a simple thermal evaporation and vapor transport method in an oxidizing environment. The as-synthesized nanowires were coated with gold to allow excitation of surface plasmons over a broad frequency range. SERS studies with near-IR excitation at 785 nm showed significant enhancement (average enhancement >10(6)) with excellent reproducibility to detect monolayer concentrations of 4-methylbenzenethiol (4-MBT) and 1,2-benzendithiol (1,2-BDT) probe molecules. The Raman enhancement showed a strong dependence on the gold film thickness, and the peak enhancement was observed for a similar to 40-nm-thick film. The Raman enhancement was stronger for randomly oriented nanowires compared to aligned ones suggesting the importance of contributions from the junctions of nanowires. Copyright (C) 2009 John Wiley & Sons, Ltd.