Research On The Heat Transport Process Of Gold Nano-film Based On Transient Heat Reflection

The critical dimension of integrated circuits are decreasing,the problem of local overheating caused by running device can not be ignored.Therefore,understanding the heat transport of the micro-nano structure and microelectronic devices at micro-nano scale is very important for the future development.We use the gold nanofilm as the main study object,which is compared with copper nanofilm.Based on dieletric function,transient two-temperature model and thermoreflectance method,the theoretical simulation and experimental research of heat transfer process are performed,which happens in the time scale for picosecond and femtosecond magnitude.The dielectric function of the metal varies with the wavelength and temperature.combining Fermi smearing and Lorentz-Drude model in the visible and near infrared region,the real and the imaginary part of the dielectric function for the gold nanofilm are derived with the change of the wavelength at different temperatures.Two-temperature model is used to simulate the interaction between ultrafast pulse and gold nanofilm,and the variation of electron and phonon temperature with delay time is obtained.The phonon temperature in the early stage of optical pumping is low.The change of transient reflectivity and refractive index is main caused by the change of electron temperature,and the relationship between transient reflectivity and temperature can be obtained.The thermal transport process of gold and copper nanofilms is studied by using dualwavelength transient reflection technique,the non-equilibrium relaxation process of gold nano films is measured.The addition of transient transmission and reflection signals can be achieved by using an adder.The two-temperature model and Crude approximation are used to fit the experimental results.It is found that the transient reflectivity and transmittance of the film change corresponding with the heat transfer process.In order to study the interaction between translucent metal nanofilms and ultra-fast laser pulses,both transmission and reflection should be considered simultaneously.It is pointed out that the obvious difference between transient reflection and transmission is the sign of transient transmission is invert,and the reason of this phenomenon is the substrate material and the temperature gradient along with the direction of the film thickness.Transient reflection technique using supercontinuous white light is used to study the ultrafast dynamic process of gold nanofilm.It is found that there is an obvious bleaching signal at 490 nm,which is due to the excitation of high energy adiabatic carriers.There is an excited absorption signal at 530 nm,The relaxation time is proportional to the pump energy.the phonon-phonon interaction caused by the substrate can not be ignored during analizing the electron and phonon temperature relaxation stage.