Tunable Plasmonic SERS “Hotspots” on Au-Film Over Nanosphere by Rapid Thermal Annealing

In this work, a novel method 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 (EFSERS) 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 AuFON 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 reinforcement was demonstrated by (EFSERS) value of 1.08 × 10
⁸
by 750 °C of RTA. Overall, a downscaled nonlithographic SERS substrate with tunable plasmonic response by RTA process was successfully fabricated.