Hierarchical nanospheres for SERS-active substrates: design, fabrication, and performance assessment

In this work, we proposed new SERS-active substrates based on hierarchical structures of plasmonic assisted nanospheres (HSNs) and fabricated by self-assembling approaches. The hierarchical architecture exploits the advantages of the well-known ordered configuration of hexagonally closed packed array (CPA) of nanospheres. A further layer of upper nanospheres is used to provide regular and intense hotspots, located at the nanogaps between neighboring nanospheres. Numerical analyses were provided to establish the design guidelines and insights into factors affecting SERS response, and to identify the promising architectures. HSNs structures have been fabricated and morphologically characterized. Experimental analysis of the SERS response demonstrates that HSNs can work as cost-effective SERS substrates with superior performances with respect to the simpler single layer CPA configurations.