Swift Heavy Ion irradiated Pd_Au Nanocomposite Thin Films for SERS Applications

Plasmonic nanoparticle-based SERS substrates have proved their excellence in trace detection of hazardous molecules. The present work reports on ion irradiated palladium gold (Pd_Au) nano composite thin films for SERS application. The Pd_Au thin films are deposited on Si substrates by sputtering method. Further, ion irradiation at various fluences of $3\times 10^{12},1\times 10^{13}$, and $3\times 10^{13}\text{ions}/\text{cm}^{2}$ is carried out on these samples by 120 MeV silver ions. The morphology, compositional analysis and phase were characterized by SEM, RBS, and XRD techniques respectively. The pristine and irradiated samples were tested for trace level detection of an analyte molecule, Methylene Blue (MB). A lowest detection limit of $\sim 5\ \mu \mathrm{M}$ was observed for the sample irradiated with highest fluence ($3\times 10^{13}$) while $\sim 50\ \mu \mathrm{M}$ was detected in the case of other two samples. Enhancement factors of $0.67\times 10^{2},0.75\times 10^{2}$, and $2\times 10^{2}$ were observed for the samples irradiated at $3\times 10^{12},1\times 10^{13}$, and $3\times 10^{13}$, respectively. Hence, it is very clear that the irradiation fluence has a desirable effect on the SERS response of the thin films. The difference in SERS response may be attributed to the observed surface morphology changes (grain size variation) upon irradiation. We believe that further experiments with different irradiation conditions and thickness of the composite thin film may increase the enhancement factors.