Formation of nanostructures by an intense femtosecond pulse laser irradiating Au film on sapphire substrate

摘要

We investigate the morphology change of Au film on sapphire substrate by irradiating with a 1 kHz femtosecond pulse laser. Under observation of a scanning electron microscope, a textured nanostructure was formed in the exposed area on Au film due to laser ablation and subsequent stress relaxation. This process was strongly determined by the laser intensity profile and the dynamics of molten liquid. With the increasing of laser pulses number, the Au film was broken down and then a few polarization-dependent nanoripples arranged in the same direction appeared on the sapphire surface, which may result from a spatial modulation of energy due to the interference between the incident light and the excited surface plasmon polaritons. In addition, we used an energy dispersive spectrometer to analyze the chemical composition of nanoripples on the surface and in the ablated crater, respectively. The changes of O and Al elements implied that a complicated chemical transformation participated in the nanoripples formation process. We believe that present results are very useful for the analysis of the interaction between femtosecond laser and solids, especially the film material.