Spontaneously formed dense Cu nanoislands and superior SERS properties of Cu nanoislands/Cu-Ta-Mo films

Abstract

The co-sputtering method was utilized for preparing Cu-Ta-Mo films. The results indicate that the micromorphology of Cu-Ta-Mo films depends on the composition and annealing temperature. It is worth that the deposited Cu-Ta-Mo films surface was without nanoislands, and substantial quantities of Cu nanoislands are self-formed on the film's surface after annealing. The analysis indicates that the main reason for the Cu nanoislands formation is phase separation, due to atomic diffusion. Notably, the Cu grains in Ta-Cu-Mo films are surrounded by Ta- and Mo-rich amorphous areas, inhibiting the Cu grains’ growth and leading to the formation of nanoislands. In addition, annealing could promote atomic diffusion, thus facilitating Cu nanoislands’ formation and growth. The size and quantity of nanoislands influence the surface-enhanced Raman scattering (SERS) properties of Cu-Ta-Mo films. Furthermore, covering 10 nm Ag film on Cu nanoislands/Cu-Ta-Mo films’ surface could significantly enhance the SERS property, attributed to a synergistic enhancement of the electric field between Ag film and Cu nanoislands. The Ag film/Cu nanoislands/ Cu-16.34 at% Ta-13.05 at% Mo film applied to SERS substrate has high stability and sensitivity, and the limiting concentration for detecting the Raman characteristic spectra of Rhodamine 6G (R6G) solution can reach 5 × 10−14 M.