Study of the Electron–Phonon Relaxation in Thin Metal Films Using Transient Thermoreflectance Technique

Electron–phonon (e–ph) relaxation in thin metal films is an important consideration in many ultra-small and ultra-fast applications. In this work, e–ph relaxation in thin gold and aluminum films has been studied using the transient thermoreflectance technique which is demonstrated sensitive enough to study the relaxation process. The optical properties of the thin metal films are different from those of bulk metal and have been measured. Based on confirmation of the measurements, the effects of metal type, film thickness, and interface on e–ph relaxation have been experimentally studied. The thermoreflectance traces of gold and aluminum films have been compared. The results show that the e–ph relaxation and the effect of electron and lattice temperatures on the thermoreflectance of gold and aluminum are quite different. The e–ph relaxation is independent of film thickness and interface.