Phonon transport across multi-layered structure subjected to laser short irradiation pulse

Abstract

Energy transfer across a multi-layered structure, consisting of the aluminum–silicon–aluminum thin films and minute vacuum gaps at the film interfaces, is investigated. Laser short pulse irradiation is introduced at the free surface of the first aluminum film and Lambert’s Beer law is adopted to account for the absorption of the irradiated energy within the aluminum film. The transient and frequency dependent Boltzmann equation is incorporated to predict phonon transport characteristics. Equivalent equilibrium temperature is introduced to assess the phonon intensity distribution in the multi-layered structure. Since electron and lattice sub-systems thermally separate during the laser short pulse irradiation, electron–phonon coupling is incorporated in the aluminum film to model the thermal transport across the electron and lattice sub-systems. Near filed radiation is introduced across the vacuum gaps for the energy transfer at the film interfaces. It is found that equivalent equilibrium temperature in the first aluminum and the silicon film is influenced by the size of the vacuum gap located at the silicon–aluminum interface. The contribution of the ballistic phonons to the energy transfer across the minute size vacuum gap is larger than that of the near field radiation; however, increasing the gap size slightly lowers the ballistic phonon contribution.