Influence of defects on extreme ultraviolet laser ablation of LiF

We study the influence of defects (neutral Li⁰ and F⁰) on the extreme ultraviolet (XUV) laser-induced ablation of 10-nm-thick LiF films. Our method combines a molecular-dynamics scheme for LiF and a set of equations describing the temporal evolution of the conduction-electron density and temperature. We find that defects may decrease the ablation threshold by a factor of around 4. This is caused by the lattice destabilization and the tensile pressure the defects induce upon creation. Metallic colloids form due to the high mobility of Li⁰ in the heated crystal. Inhomogeneous defect distributions are shown to be even more effective for crack formation and ablation. In the extreme case, when the thermal heating induced by the laser is negligible and only the effect of defect formation is considered (“cold ablation”), LiF spalls in the solid state.