Study on ultra fast nonequilibrium heat transfers in nano metal films by femtosecond laser pump and probe method

Abstract

The reduction in size and the increase in speed of microelectronic device make the probability of nonequilibrium electron-phonon phenomena become greater, leading to the increase of thermal resistance in the device. The measurement of electron-phonon coupling factor in material resistance increasingly becomes important for accurate thermal treatment. The femtosecond laser pump and probe method is used for studing the nonequilibrium heat transfer in nano metal films with different thicknesses. Exploring parabolic two-step model (PTS) to fit the experimental data. During the fitting process, we considered the proportional relationship between the changes of electron temperature and phonon temperature, which affects the reflectivity. By studying the different thicknesses of Ni and Al films electron-phonon coupling factors, we find that the electron-phonon coupling factor does not change with film thickness. In addition, the experimental result verifies that the reflectivity of probe laser is affected by electron temperature and phonon temperature at the same time. Through the data analysis, we also get the influence coefficients of electron temperature and phonon temperature on reflectivity.