Medvedev Nikita, Milov Igor
Institute of Physics, Czech Academy of Sciences, Na Slovance 1999/2, 18221 Prague, Czech Republic.
Institute of Plasma Physics, Czech Academy of Sciences, Za Slovankou 3, 18200 Prague, Czech Republic.
Materials (Basel). 2022 Jul 13;15(14):4883. doi: 10.3390/ma15144883.
Laser irradiation of metals is widely used in research and applications. In this work, we study how the material geometry affects electron-phonon coupling in nano-sized gold samples: an ultrathin layer, nano-rod, and two types of gold nanoparticles (cubic and octahedral). We use the combined tight-binding molecular dynamics Boltzmann collision integral method implemented within XTANT-3 code to evaluate the coupling parameter in irradiation targets at high electronic temperatures (up to ~20,000 K). Our results show that the electron-phonon coupling in all objects with the same fcc atomic structure (bulk, layer, rod, cubic and octahedral nanoparticles) is nearly identical at electronic temperatures above ~7000 K, independently of geometry and dimensionality. At low electronic temperatures, reducing dimensionality reduces the coupling parameter. Additionally, nano-objects under ultrafast energy deposition experience nonthermal damage due to expansion caused by electronic pressure, in contrast to bulk metal. Nano-object ultrafast expansion leads to the ablation/emission of atoms and disorders the inside of the remaining parts. These nonthermal atomic expansion and melting are significantly faster than electron-phonon coupling, forming a dominant effect in nano-sized gold.
金属的激光辐照在研究和应用中被广泛使用。在这项工作中，我们研究了材料几何形状如何影响纳米尺寸金样品中的电子 - 声子耦合：超薄层、纳米棒以及两种类型的金纳米颗粒（立方体形和八面体形）。我们使用在XTANT - 3代码中实现的结合紧束缚分子动力学玻尔兹曼碰撞积分方法，来评估在高电子温度（高达约20,000 K）下辐照靶中的耦合参数。我们的结果表明，在电子温度高于约7000 K时，所有具有相同面心立方原子结构的物体（体材料、层、棒、立方体形和八面体形纳米颗粒）中的电子 - 声子耦合几乎相同，与几何形状和维度无关。在低电子温度下，降低维度会降低耦合参数。此外，与体金属相比，超快能量沉积下的纳米物体由于电子压力引起的膨胀而经历非热损伤。纳米物体的超快膨胀导致原子的烧蚀/发射，并使其余部分内部无序。这些非热原子膨胀和熔化比电子 - 声子耦合快得多，在纳米尺寸的金中形成主导效应。
