Highly Ordered Ag/Cu Hybrid Nanostructure Arrays for Ultrasensitive Surface-Enhanced Raman Spectroscopy

Despite significant progress recently made in this field, the practical application of surface-enhanced Raman spectroscopy (SERS) is frequently limited by the lack of highly sensitive, reproducible, and cost-effective substrates. The fabrication of SERS substrates with a consistently high density of hot-spots is a key step to address this issue. Here, a simple approach is reported for the fabrication of Ag/Cu hybrid nanostructure arrays as highly sensitive and cost-effective substrates for SERS application. By effectively tuning the gap size between neighboring nanorods to sub-10 nm and increasing the packing density of nanorods, ordered Cu nanorod arrays can be used as cheap and effective SERS substrates in their own right. After sputtering a very thin layer of Ag nanoparticles on the surface of the Cu nanorods to get sub-5 nm gaps, further field enhancement is enabled. A cascaded field enhancement has been evidenced by the electromagnetic simulations. The Ag/Cu hybrid nanostructure arrays exhibit a detection limit down to 10⁻¹⁵ m for nonresonant molecules such as benzenethiol.