Microstructure evolution and highly sensitive surface enhanced Raman scattering properties of self-formation dual-scale Ag nanoparticles/ Ag-Zr alloy film

Abstract

• Simple method was proposed to prepare monodisperse Ag particles/Ag-Zr films. • Ag nanoparticles (NPs) directly formed on the surface of as-deposited Ag-Zr films. • Size, number and nanogap of Ag NPs are sensitive to Ag-Zr film thickness. • Ag NP/Ag-Zr granular film displays effective Raman enhanced properties. Ag-22%Zr alloy films with different thicknesses were fabricated on flexible polyimide substrate by co-sputtering method. It is interested in finding that a lot of Ag nanoparticles are spontaneously formed on the as-deposited Ag-Zr films at room temperature. The phase, crystal structure, particle number and size, and surface enhanced Raman scattering (SERS) properties of as-deposited and annealed Ag-Zr alloy films were characterized by X-ray diffraction, high resolution transmission electron microscope, field emission scanning electron microscope and Raman spectrometer, respectively. Results show that Zr grains dispersed around Ag grains and had a coherent growth relation with Ag grains in the alloy film. Dual scale Ag nanoparticles were formed on the annealed Ag-Zr alloy films without template. An intense SERS effect was obtained by covering the Ag layer on the Ag-Zr alloy films. The SERS substrate showed good repeatability and revealed high sensitivity of enhancement factor with the detection limit concentration of Rhodamine 6G as low as 5 × 10-15 mol/L. It was demonstrated that the nanogaps between Ag nanoparticles behaved as hot spots, and thus enhanced local electromagnetic fields substantially. Furthermore, densely and uniformly distributed Ag nanoparticles enlarged the surface roughness and the surface area, resulting in further enhanced Raman signals.