Abnormal microstructure evolution behaviors of annealed Ag-18.9 at% Co alloy film on flexible polyimide substrates

Ag-Co alloy films were fabricated at room temperature by magnetron sputtering. The results revealed that a large amount of polyhedral single-crystal Ag nanoparticles grow on the surface of Ag-Co alloy films, which is significantly different from the microstructure of Ag-Co alloy films on rigid substrates. Furthermore, after annealing, Ag atoms get enough energy to move toward the film surface and thus the mass and average size of Ag particles both increase with the increase of annealing temperatures. In addition, the average size of Ag particles decreases with the increase of annealing time but the particles per square micron increases. Amorphous Co is observed in the Ag-Co films and Ag grains in Ag-Co films become smaller, which indicates the growth of Ag grains is inhibited by Co. A new type of Ag particles / Ag-Co films with a convex structure is obtained and applied as SERS substrates, where the characteristic Raman spectra of 5 × 10−12 M R6G could be detected.