Structural instability of transition metals upon ultrafast laser irradiation

Precision in laser material structuring is critically defined by the energy flow during irradiation process, particularly ultrafast regimes. Alternative to thermal evolutions, nonequilibrium electronic excitation can exercise a direct influence on atomic bonding delivering potentially rapid destructuring process. In this context, disordering of transition metals (Cr, Ni, and Ti) induced typical for processing studied with an emphasis role $d$-band filling crystalline structure. The density functional theory used obtain, from first principles, structural stability criteria nonthermal pathways timescales shorter than picosecond electron-phonon dynamics. We show that hot electrons distort charge distribution cold arrangement increase entropy system, thus driving mechanical expansion. calculated free-energy potentials indicate solid destabilization possible when electron temperature reaches universal value around 2 eV all considered metals. Under uniaxial lattice relaxation expected ablation surface layers, redistribution loss shown be oriented along specific crystal directions. Moreover, we interatomic potential energetically more favorable Ni Cr Ti. Lattice dynamics affected space-charge Fermi smearing associated anisotropic expansion due pressure gradients. This mechanism general feature partially filled