Femtosecond Laser Irradiation of a Multilayer Metal–Metal Nanostructure

The selective modification of upper layers of a Ni/Al multilayer nanostructure irradiated by a single femtosecond laser pulse has been studied. The analysis of surface topography indicates that either partial or complete removal of two upper layers is possible depending on the absorbed energy. The surface has been scanned by an atomic force microscope. The numerical simulation of the phenomenon with a two-temperature hydrodynamic code has revealed an asynchronous dynamics of the electron subsystems of Ni and Al and an inhomogeneous heating of ion subsystems. As a result, a complex combination of compression and rarefaction waves is initiated in the multilayer target. It has been shown numerically that, as the absorbed energy increases, the first nickel layer is initially ruptured because of the localization of tensile stresses. The experimental and numerical thicknesses of the separated layer and the threshold energy are in agreement with each other. Consequently, the parameters of two-temperature models of nickel and aluminum are selected correctly.