Different Effects of Annealing on Microstructure Evolution and SERS Performance for Cu–Cr Alloy Film and Bulk Alloy

Copper–chromium alloy film and Cu–Cr bulk alloy were obtained using magnetron sputtering and vacuum smelting. Experimental results indicated that Cu–Cr bulk alloy and alloy films having different residual stress and atomic diffusion exhibit a significant difference in microstructure evolution behaviors after annealing. Numerous polyhedral Cu particles and dendritic Cr particles precipitated on the surface of annealed Cu–Cr alloy film and as–cast Cu–Cr bulk alloy, respectively. Cu particles were formed under the driving of energy and residual stress in the film. The effect of annealing temperature and Cr content on the size and quantity of Cu particles is discussed. Cr particles precipitated on the bulk alloy due to the low solid solubility of Cr in Cu, and the crystallinity of Cu grains promoted the diffusion of Cr atoms. The surface–enhanced Raman scattering (SERS) intensity of the Cu–14.6%Cr alloy film was obviously higher than that of the Cu–14.2%Cr bulk alloy. The particles/film composite structure possessed the appropriate particle number, surface roughness, and interstitial gap, as opposed to the bulk material, to effectively improve SERS enhancement.