Tunable Plasmonic SERS Hotspots on Au-Film over Nanosphere by Rapid Thermal Annealing

In thiswork, a novelmethod combining fabrication of nonlithographic Au-film over nanosphere (AuFON) with gradual rapid thermal annealing (RTA) treatment was developed to produce a high performance of surface-enhanced Raman scattering (SERS) substrate. The highly uniform and periodic AuFON was achieved by the downscaling processs in the modified nanosphere lithography technique using 100-nm polystyrene (PS) nanospheres, which target significant SERS enhancement factor (EF_SERS) due to effectively generated "hotspots." Two essential approaches in the nanostructure downscaling included the application of oxygen plasma or solvent ratio adjustment during PS nanospheres selfassembly drop-casting procedures. After the production of Au- FON substrates, short RTA process on the AuFON was conducted at 250 °C, 500 °C, and 750 °C, respectively, to increase surface roughness that contribute to the improved SERS activity. Results show that the higher temperature of RTA linearly resulted in structural alteration of Au-film confined on PS spherical lining, which led to an eventual enhancement of SERS response on the detection of 1 μM Rhodamine 6G Raman probe. The most effective SERS reinforcementwas demonstrated by (EF_SERS) value of 1.08×10⁸ by 750 °C of RTA. Overall, a downscaled nonlithographic SERS substrate with tunable plasmonic response by RTA process was successfully fabricated.