Abstract
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.
Highlights
Ultrafast thermomechanical responses of a 〈100〉 copper film
The main aim of the present work is to study the effect of crystal orientation on ultrafast thermomechanical responses and spallation behaviors of monocrystal copper films irradiated by femtosecond laser pulse
Monocrystal copper films with 〈100〉, 〈110〉 and 〈111〉 crystal orientations along the thickness direction are adopted to investigate the influence of crystal orientation on ultrafast thermo-mechanical responses and spallation behaviors based on molecular dynamics simulation (MDS)
Summary
Ultrafast thermomechanical responses of a 〈100〉 copper film. Their results illustrated that the electron relaxation effect can be neglected when the laser duration is much longer than the electron thermal relaxation time; but it becomes significant if the laser duration matches the electron relaxation time, especially when the former is much shorter than the latter. Few works about the influence of crystal orientation on ultrafast thermomechanical responses and spallation behaviors of single crystal metal during femtosecond laser heating has been reported up to now. The main aim of the present work is to study the effect of crystal orientation on ultrafast thermomechanical responses and spallation behaviors of monocrystal copper films irradiated by femtosecond laser pulse. To study the effect of crystal orientation on ultrafast thermo-mechanical coupling responses and spallation behaviors of monocrystal copper films, three MD models of thin copper films are created: i) a monocrystal copper target with the 〈1 0 0〉, 〈0 1 0〉 and 〈0 0 1〉 crystal orientations along the x-, y- and z-directions, respectively, which has a size of 15.2 nm × 15.2 nm × 455.5 nm and possesses 8.68 million atoms as shown in Fig. The HTTM-MD model is described as follows: HTTM: Ce(Te)
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