Department of Mechanics, Huazhong University of Science & Technology, 1037 Luoyu Road, Wuhan, 430074, China.
Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment, Luoyu Road 1037, Wuhan, 430074, China.
Sci Rep. 2017 Aug 23;7(1):9218. doi: 10.1038/s41598-017-09559-6.
Ultrafast thermomechanical responses and spallation behaviours of monocrystal copper films irradiated by femtosecond laser pulse are investigated using molecular dynamics simulation (MDS). Films with 〈100〉, 〈110〉 and 〈111〉 crystal orientations along the thickness direction were studied. The results show that the crystal orientation has a significant effect on femtosecond laser-induced thermomechanical responses and spallation behaviors of monocrystal copper films. The discrepancy between normal stresses in copper films with different crystal orientation leads to distinct differences in lattice temperature. Moreover, the copper films with different crystal orientations present distinct spallation behaviors, including structural melting (atomic splashing) and fracture. The melting depth of 〈100〉 copper film is lower than that of 〈110〉 and 〈111〉 copper films for the same laser intensity. The dislocations and slip bands are formed and propagate from the solid-liquid interface of 〈110〉 and 〈111〉 copper films, while these phenomena do not appear in 〈100〉 copper film. Additionally, numerous slip bands are generated in the non-irradiated surface region of copper films due to reflection of mechanical stress. These slip bands can finally evolve into cracks (nanovoids) with time, which further result in the fracture of the entire films.
采用分子动力学模拟（MDS）研究了飞秒激光脉冲辐照下单晶铜薄膜的超快热机械响应和层裂行为。研究了厚度方向上具有〈100〉、〈110〉和〈111〉晶体取向的薄膜。结果表明，晶体取向对飞秒激光诱导的单晶铜薄膜热机械响应和层裂行为有显著影响。不同晶体取向的铜薄膜中法向应力的差异导致晶格温度存在明显差异。此外，具有不同晶体取向的铜薄膜呈现出不同的层裂行为，包括结构熔化（原子飞溅）和断裂。对于相同的激光强度，〈100〉铜薄膜的熔化深度低于〈110〉和〈111〉铜薄膜。位错和滑移带从〈110〉和〈111〉铜薄膜的固液界面形成并扩展，而〈100〉铜薄膜中则不会出现这些现象。此外，由于机械应力的反射，在铜薄膜的未辐照表面区域产生了大量的滑移带。随着时间的推移，这些滑移带最终会演变成裂纹（纳米空穴），从而导致整个薄膜的断裂。
