Ag-Cu alloy films as robust substrates for SERS-based sensing applications

In this work, thin films of pure Ag and Ag-Cu alloys in three different compositions were deposited on silicon and quartz substrates at room temperature using DC magnetron sputtering and co-sputtering techniques. Post-deposition, all films were annealed in an inert argon atmosphere at 600 °C for 1 h. Elemental composition was confirmed by Rutherford Backscattering Spectrometry (RBS), while X-ray diffraction (XRD) verified alloy formation. Surface morphology was examined using field emission scanning electron microscope (FESEM) and atomic force microscope (AFM) imaging. The films were evaluated as surface-enhanced Raman spectroscopy (SERS) substrates using three analytes: 1 nM crystal violet, 1 nM Rhodamine 6G, and 1 mM picric acid. An analytical enhancement factor (AEF) of the order of 108was achieved for crystal violet. A key novelty of this work is the quantitative assessment of oxidative resistance in Ag and Ag-Cu alloy films specifically for SERS applications. The results demonstrate that Ag-Cu alloys maintain strong SERS performance, comparable to pure Ag, while exhibiting a threefold reduction in surface oxidation compared to pure Ag, underscoring their suitability as durable and cost-effective SERS substrates with potential industrial applications for sensing of dyes, explosives and other harmful molecules.