Synergistic enhancement of Ag layer and Cu particles on SERS property of spontaneously formed Cu nanoparticles/Ta–Cu alloy thin films

Surface-enhanced Raman scattering (SERS) is a highly accurate and ultra-sensitive single-molecule detection technology. Ta-Cu alloy thin films were prepared by co-sputtering technique at room temperature. The results have shown that as-deposited state Ta-Cu alloy thin films' surface was smooth, however, large amounts of Cu nanoparticles (NPs) were spontaneously formed on annealed alloy thin films' surface. Analysis indicated that the Ta-rich amorphous regions dispersed around Cu grains in Ta-Cu alloy thin films inhibited the growth of Cu grains and promoted the self-formation of nanoparticles on films' surface. The microscopic morphology of Ta-Cu alloy thin films can be regulated by varying the Cu content, film thickness, and annealing temperature. In addition, a 12 nm Ag covering layer on Cu NPs /Ta-Cu alloy thin films' surface could improve SERS performance by synergistic enhancement of the electric field induced by the plasmon resonance of Cu NPs and reducing the spacing between Cu NPs to enhance the local electric fields. As SERS substrates, the Ag layer/Cu NPs/Ta-Cu alloy thin films can detect the Raman characteristic spectrum of 5 × 10-12 mol·L-1 (M) rhodamine 6G (R6G) solution. This paper proposes an economical and environmentally friendly method to prepare low-cost and highly sensitive SERS substrates.