Nanostructured bi-metallic Pd–Ag alloy films for surface-enhanced Raman spectroscopy-based sensing application

In the present work, thin films of bimetallic palladium–silver (Pd50Ag50 and Pd70Ag30) alloy on silicon substrates are deposited by direct current magnetron cosputtering in a vacuum chamber at a pressure of 10−7 Torr. The formation of the alloy is confirmed by the shift of x-ray diffraction peaks as compared to the pure phases of the metals. The films are subjected to rapid thermal annealing at 500 °C for 120 s. Surface-enhanced Raman spectroscopy (SERS) is performed for low level detection of two analytes: crystal violet (dye) and tetryl (an explosive). The SERS signals are observed only in the case of the rapid thermal annealed films. The lowest concentration of the dye detected with Pd50Ag50 is 100 μM. In comparison, it is 250 μM for Pd70Ag30, indicating that a higher content of silver in the alloy is desirable from a SERS perspective due to its more robust plasmonic activity.