SERS in red spectrum region through array of Ag–Cu composite nanoparticles formed by vacuum-thermal evaporation

In order to expand the spectral capabilities of the SERS method, Ag–Cu alloy nanoparticle arrays were studied. Arrays of Ag–Cu nanoparticles were formed by vacuum thermal evaporation and condensation on an unheated substrate followed by heat treatment at 230 °C. A higher Raman scattering enhancement in the red region of the spectrum when using an array of nanoparticles of the Ag–Cu eutectic system was found. This enhancement is comparable to the one of pure silver particle array in the blue region of the spectrum. Transmission electron microscopy study has shown that the feature of the Ag–Cu array is that many particles are composite: one part consists of copper, and the other part is made up of silver. These parts have a perfect (possibly heteroepitaxial) boundary. It is believed that the localized surface plasmon resonance excited in the copper part by red light can be transmitted without any loss into the silver part, while the one excited in the silver part by blue light, quickly fades out in the copper part, because blue light has a higher frequency than the copper plasma frequency. From the point of view of SERS applications, the use of Ag–Cu particle arrays allows extending the advantage of silver to the red region of the spectrum. [Display omitted] •Maximum amplification of the Raman signal for the array of Ag–Cu particles is observed in the red region of the spectrum.•Many particles in the array are composite: one part is copper the other is silver.•The border between the copper and silver parts is perfect.