Ablation of a nanostructured metal surface by ultrashort X-ray pulses

Using molecular-dynamics simulation, we study the interaction of an ultrashort X-ray pulse with an Al surface. The surface has a periodic grating structure consisting of alternating ridges of height 80 nm and width 80 nm, separated by trenches of width 160 nm. After irradiation with an ultrashort (0.2 ps) X-ray pulse with a fluence above the ablation threshold we observe that the ridges first disintegrate into a foamy mixture of melt and gas bubbles, which grow faster than those in the trenches. Due to the interference of tensile pressure build-up below the ridges and the trenches, the material does not spall. At the concave edges, jets are emitted with velocities of around 1000 m/s, which may ultimately lead to the creation of finer surface structures.