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首页> 外文期刊>Journal of Heat Transfer >Modeling Electron-Phonon Nonequilibrium in Gold Films Using Boltzmann Transport Model
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Modeling Electron-Phonon Nonequilibrium in Gold Films Using Boltzmann Transport Model

机译：使用玻尔兹曼输运模型模拟金膜中电子-声子非平衡

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Ultrashort-pulsed laser irradiation on metals creates a thermal nonequilibrium between electrons and the phonons. Previous computational studies used the two-temperature model and its variants to model this nonequilibrium. However, when the laser pulse duration is smaller than the relaxation time of the energy carriers or when the carriers' mean free path is larger than the material dimension, these macroscopic models fail to capture the physics accurately. In this paper, the nonequilibrium between energy carriers is modeled via a numerical solution of the Boltzmann transport model (BTM) for electrons and phonons, which is applicable over a wide range of lengths and time scales. The BTM is solved using the discontinuous Galerkin finite element method for spatial discretization and the three-step Runge-Kutta temporal discretization. Temperature dependent electron-phonon coupling factor and electron heat capacity are used due to the strong electron-phonon nonequilibrium considered in this study. The results from the proposed model are compared with existing experimental studies on laser heating of macroscale materials. The model is then used to study laser heating of gold films, by varying parameters such as the film thickness, laser fluence, and pulse duration. It is found that the temporal evolution of electron and phonon temperatures in nanometer size gold films is very different from the macroscale films. For a given laser fluence and pulse duration, the peak electron temperature increases with a decrease in the thickness of the gold film. Both film thickness and laser fluence significantly affect the melting time. For a fluence of 1000 J/m~2, and a pulse duration of 75 fs, gold films of thickness smaller than 100 nm melt before reaching electron-phonon equilibrium. However, for the film thickness of 2000 nm, even with the highest laser fluence examined, the electrons and phonons reach equilibrium and the gold film does not melt.
机译：金属上的超短脉冲激光辐照会在电子和声子之间产生热不平衡。先前的计算研究使用双温度模型及其变体对这种非平衡进行建模。但是，当激光脉冲持续时间小于能量载体的弛豫时间时，或者当载体的平均自由程大于材料尺寸时，这些宏观模型将无法准确地捕获物理学。本文通过电子和声子的玻尔兹曼输运模型（BTM）的数值解对能量载体之间的不平衡进行建模，该模型适用于各种长度和时间尺度。使用不连续Galerkin有限元方法对空间离散化和三步Runge-Kutta时间离散化求解BTM。由于本研究中考虑到了强烈的电子-声子非平衡性，因此使用了取决于温度的电子-声子耦合因子和电子热容量。所提出模型的结果与现有的大型材料激光加热实验研究进行了比较。然后，通过改变诸如膜厚，激光通量和脉冲持续时间之类的参数，将模型用于研究金膜的激光加热。发现纳米尺寸金膜中电子和声子温度的时间演化与宏观膜有很大不同。对于给定的激光通量和脉冲持续时间，峰值电子温度随着金膜厚度的减小而增加。膜厚和激光能量密度均会显着影响熔化时间。对于注量为1000 J / m〜2，脉冲持续时间为75 fs，厚度小于100 nm的金膜在达到电子-声子平衡之前就熔化了。但是，对于2000 nm的膜厚，即使检查的激光通量最高，电子和声子也达到平衡，金膜不会熔化。

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