Lattice response to the relaxation of electronic pressure of ultrafast laser-irradiated copper and nickel nanofilms

J Zhang and XL Cheng and NL He and GQ Yan, JOURNAL OF PHYSICS-CONDENSED MATTER, 30, 085401 (2018).

DOI: 10.1088/1361-648X/aaa642

The impact of electronic pressure and electronic pressure gradient induced by laser excitation on the dynamic response of metals (Cu and Ni) has been numerically investigated using two complementary approaches. In the framework of DFPT, for electronic temperatures up to 6 eV, we demonstrate that electronic pressure results in a higher lattice stability. In other words, the electronic pressure has a negative influence on the phonon entropy and induces an increase in the shear modulus, which improves the melting temperature and lattice vibration frequency. Given the relaxation of electronic pressure during an extreme non-equilibrium state, we adopt a modified 2T-MD model to identify the contribution of the electronic pressure gradient to the atomic dynamics during fs laser excitation. Our results indicate the presence of rapid destabilization of the structure of Cu and Ni nano- films along the electronic pressure gradients. Specifically, the nucleation of the voids and heterogeneous nucleation occur at the surface layer, at a depth of several nanometers, for Cu and Ni, respectively. With the coexistence of a-thermal and thermal effects on scales, two different ultrafast destructuring processes of Cu and Ni both interrelate a hot electronic blast force and classical electron-ion dynamics.

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