fabrication of sub-10-nm plasmonic gaps for ultra-sensitive raman spectroscopy

The past two decades have witnessed the explosion of activities in the field of surface enhanced raman spectroscopy (sers). sers platforms employ nano-structures that excite plasmonic modes with large local electromagnetic fields localized within small gap spaces between each constituting feature. although the research-oriented sers platforms yield significant signal enhancements to identify even single molecules, practical sers-based sensors have not been fully introduced yet. the main reason behind this absence is the need for a cost-effective and reliable manufacturing method for controllable fabrication of plasmonic nano-gaps over large areas. in this article, we introduced a novel manufacturing process that enables fast and scalable fabrication of highly uniform sub-10-nm gaps that could yield large sers signals. in this process, a conventional electroplating technique is used to produce unique nano-mushroom antenna arrays on a conducting substrate, resulting in controllable gap spaces between mushroom heads. by understanding the nature of mushroom shape antenna formation, we demonstrated the control of inter-metallic gaps down to 5 nm. we showed that the manufactured nano-structures yield raman enhancements more than 108. providing such large sers signals that are uniform over large areas, our cost-effective fabrication technique could be very critical to realize practical sers devices.