Runaway lattice-mismatched interface in an atomistic simulation of femtosecond laser irradiation of Ag film–Cu substrate system
Runaway lattice-mismatched interface in an atomistic simulation of femtosecond laser irradiation of Ag film–Cu substrate system
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DOI：
10.1007/s00339-011-6436-7
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发表时间：
2011-05
期刊：
影响因子：
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通讯作者：
Chengping Wu;Derek A. Thomas;Zhibin Lin;L. Zhigilei
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文献类型：
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作者：
Chengping Wu;Derek A. Thomas;Zhibin Lin;L. Zhigilei
本文研究了飞秒激光辐照银膜-铜衬底体系中的原子混合和结构转变。该模型采用经典分子动力学方法和连续能级描述激光激发和导带电子随后的弛豫。Cu中的电子-声子耦合强度高于Ag，导致Cu衬底优先在亚表面加热和熔化。在低于Cu和Ag的平衡熔化温度的强过冷条件下，熔解后是快速冷却和快速再凝固。快速再凝固导致界面区域结构复杂，在再凝固过程的最后阶段，在fcc Ag膜的（001）表面外延生长的中间伪晶bcc Cu层将晶格不匹配的界面与Ag - Cu混合区分开。新的晶格错配界面具有由阶梯杆部分位错勾勒出的周期性层错金字塔阵列组成的三维结构。中间的bcc层和错配界面的叠错金字塔结构可能为位错的传播提供了强大的屏障，导致激光辐照后层状结构的有效硬化。与平衡Cu - ag界面的宽度相比，原子混合区的浓度分布要宽得多，并且具有明显的不对称形状，这反映了Cu衬底的优先熔化。
The atomic mixing and structural transformations in a Ag film–Cu substrate system irradiated by a femtosecond laser pulse are investigated in a simulation performed with a model that couples the classical molecular dynamics method with a continuum-level description of the laser excitation and subsequent relaxation of the conduction-band electrons. The higher strength of the electron–phonon coupling in Cu compared to Ag results in preferential sub-surface heating and melting of the Cu substrate. The melting is followed by fast cooling and rapid resolidification occurring under conditions of strong undercooling below the equilibrium melting temperatures of Cu and Ag. The rapid resolidification results in a complex structure of the interfacial region, where the lattice-mismatched interface is separated from the Ag–Cu mixing region by an intermediate pseudomorphic bcc Cu layer that grows epitaxially on the (001) face of the fcc Ag film during the final stage of the resolidification process. The new lattice-mismatched interface has a three-dimensional structure consisting of a periodic array of stacking fault pyramids outlined by stair-rod partial dislocations. The intermediate bcc layer and the stacking fault pyramid structure of the mismatched interface are likely to present a strong barrier for dislocation propagation, resulting in the effective hardening of the layered structure treated by the laser irradiation. The concentration profiles in the atomic mixing region are substantially wider compared to the width of the equilibrium Cu–Ag interface and have a pronounced asymmetric shape that reflects the preferential melting of the Cu substrate.