Fabrication of Ion Beam–Modified Flexible Plasmonic-Based Au-ITO-PET Substrates for SERS Applications

The thermal evaporation technique was utilized to deposit a gold (Au) thin film on commercial Indium Tin Oxide (ITO)–coated Polyethylene Terephthalate (ITO-PET) sheets. These Au-deposited sheets of ITO-PET were subsequently irradiated by 10 keV Ar⁺ ions at fluences of 1 × 10¹⁶ and 3 × 10¹⁶ ions/cm². The thickness of Au and ITO-PET following irradiation of the pristine and irradiated samples were then investigated using the Rutherford backscattering (RBS) experiment. The film with the highest irradiation demonstrated a maximum decrease in the thickness of Au when compared to the as-prepared Au film. FESEM data suggests an observable change in the morphologies, but interestingly, Au-ITO-PET irradiated at a fluence of 3 × 10¹⁶ ions/cm² showcases an interesting morphology of rod-like structures with globules connected and with nano-holes on the surface. Further, the EDAX analysis confirms the decrease of Au, which is analogous to results obtained from RBS. The pristine and irradiated Au surface roughness on ITO-PET samples increased with irradiation, as analyzed using atomic force microscopy. The transmission spectra for these samples were studied using UV–visible absorption spectroscopy. A minimum was observed at 560 nm for Au-ITO-PET irradiated substrate at a fluence of 3 × 10¹⁶ ions/cm², showcasing the plasmonic properties due to the formation of Au nanostructures. The pristine and the ion-modified substrates were examined as SERS substrates for detecting RhB dye as an analyte at concentrations of micro-M (µM) and nano-M (nM). Interesting results were obtained showing Raman modes for PET and RhB. These experiments lay a new area of research on polymer as a substrate for SERS with the presence of noble metals. Surface roughness and formation of plasmonic metal nanostructures are two critical parameters for SERS. The work here reports and investigates how a polymer as a base substrate affects SERS detection using ion beam modification.