Atomistic modeling of pulsed laser ablation in liquid: spatially and time-resolved maps of transient nonequilibrium states and channels of nanoparticle formation
Atomistic modeling of pulsed laser ablation in liquid: spatially and time-resolved maps of transient nonequilibrium states and channels of nanoparticle formation
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DOI：
10.1007/s00339-023-06525-0
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发表时间：
2023-03
期刊：
影响因子：
--
通讯作者：
Chaobo Chen;L. Zhigilei
中科院分区：
文献类型：
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作者：
Chaobo Chen;L. Zhigilei
通过一系列大规模的原子级模拟，研究了皮秒脉冲激光在液体中烧蚀FeNi靶的机理。模拟揭示了三种注量制度的存在，其具有不同的材料喷射和纳米颗粒形成的主导机制。这些是（1）低注量区域，其中通过金属原子的蒸发形成原子簇和小纳米颗粒，随后在烧蚀羽流的前部的低密度区域中冷凝，（2）中等注量区域，其中互连液体区域的瞬时海绵状结构的顶部的粗糙化和分解导致大纳米颗粒的形成，以及（3）高注量区域，其中纳米颗粒主要在相分离前沿形成，该相分离前沿传播通过烧蚀羽流，该烧蚀羽流通过相对于液体环境膨胀并与液体混合而从超临界状态冷却。最大的纳米粒子的产生是在中等注量制度中观察到的，并且在过渡到高注量制度时，纳米粒子的最大尺寸和材料转化为纳米粒子的能量效率都降低。一些纳米粒子经历极端的淬火速率，并在深过冷的条件下迅速固化，产生大量的缺陷丰富的纳米粒子的实际应用的兴趣。模拟的结果被映射到由具有高斯空间分布的光束照射的激光光斑内实现的条件，其中在激光光斑的不同部分中同时激活不同的烧蚀制度。在模拟中预测的瞬态非平衡状态的空间和时间分辨的地图提供了一个全面的烧蚀动力学和烧蚀过程的初始阶段的时间分辨实验探测的结果的解释的坚实基础。
The mechanisms of picosecond pulse laser ablation in liquid are investigated in a series of large-scale atomistic simulations performed for FeNi targets irradiated in a liquid environment by picosecond laser pulses at a broad range of fluences. The simulations reveal the existence of three fluence regimes featuring different dominant mechanisms of material ejection and nanoparticle formation. These are (1) the low fluence regime, where atomic clusters and small nanoparticles form through the evaporation of metal atoms followed by condensation in a low-density region at the front of the ablation plume, (2) the medium fluence regime, where roughening and decomposition of a top part of a transient spongy structure of interconnected liquid regions leads to the formation of large nanoparticles, and (3) the high fluence regime, where the nanoparticles form primarily at the phase separation front propagating through the ablation plume cooled from the supercritical state by expansion against the liquid environment and mixing with the liquid. The generation of the largest nanoparticles is observed in the medium fluence regime, and both the maximum size of the nanoparticles and the energy efficiency of the material conversion into nanoparticles decrease upon transition to the high fluence regime. Some of the nanoparticles experience extreme quench rates and rapidly solidify under conditions of deep undercooling, yielding a population of defect-rich nanoparticles of interest for practical applications. The results of the simulations are mapped to the conditions realized within a laser spot irradiated by a beam with a Gaussian spatial profile, where different ablation regimes are activated simultaneously in different parts of the laser spot. The spatially and time-resolved maps of the transient nonequilibrium states predicted in the simulations provide a comprehensive picture of the ablation dynamics and a solid foundation for interpretation of the results of time-resolved experimental probing of the initial stage of the ablation process.