Experiment study of the size effects on electron-phonon relaxation and electrical resistivity of polycrystalline thin gold films

The electron-phonon relaxation and electrical resistivity of several polycrystalline thin gold films with different thickness have been investigated using the transient thermoreflectance technique and standard four-probe method, respectively. The results show that the electron-phonon relaxation is nearly the same as that of bulk gold and independent of film thickness, while the electrical resistivity greatly increases compared to the bulk value and tends to decrease as films become thicker. These discrepancies indicate quite a different influence of size effects on electron-phonon relaxation and electrical resistivity of polycrystalline thin gold films. We identify the mechanisms by which size effects influence the electron-phonon relaxation and electrical transport and explain why size effects alter them in different way.