The effect of enhanced heat transfer across metal-nonmetal interfaces subject to femtosecond laser irradiation

The heat transfer across metal-nonmetal interfaces inevitably affects the femtosecond laser processing of thin metal films coated on nonmetal substrates. In the present work, a two-temperature model with a metal-nonmetal interface is employed to numerically investigate the heat transfer across a metal-nonmetal interface. A parallel-series thermal circuit is considered under the drastic electron-phonon nonequilibrium induced by femtosecond laser irradiation. The interfacial thermal resistance affects temporal evolutions of surface electron temperature and phonon temperature, as well as the optical response simulated by the Drude-Lorentz model. By inserting an interlayer and reducing the interfacial thermal resistance, the enhanced heat transfer across Au-Al₂O₃ and Au-Si interfaces is confirmed. More heat transfers from a metal to a nonmetal due to lower total interfacial thermal resistance, which reshapes the temperature distributions of metal-electrons, metal-phonons, and nonmetal-phonons. Consequently, the higher damage threshold of thin Au films and the lower sensitivity of damage threshold versus film thickness are determined. It implies that the heat transfer across metal-nonmetal interfaces is found to affect the transient thermal reflectivity detection and the repeatable femtosecond laser processing of thin metal films.