Optical and microstructural characterisation of Au-Sn and Cu-Sn diffusive layers

► We determined phase composition, optical and electrical properties of Au-Sn and Cu-Sn ultra-thin films. ► The samples were characterised using the XRD, SEM, SE and transmittance measurements. ► Creation of intermetallic phases at room temperature was revealed in both types of samples. ► The effective complex dielectric functions and optical conductivity were determined. ► The optical resistivity of multiphase films agreed reasonably with the dc-resistivity results.