Nano-meter scale modifications on material surfaces induced by soft x-ray laser pulse irradiations

To study the interactions between a soft x-ray laser (SXRL) and various materials, we irradiated Al, Au, Cu, and Si with the SXRL beam pulses having a wavelength of 13.9 nm and duration of 7 ps. Following the irradiation, the induced structures were observed using a scanning electron microscope and an atomic force microscope. With single pulse irradiation, conical structures were observed on the Al surface, and ripple-like structures were formed on the Au and Cu surfaces. The conical structures were destroyed under multiple SXRL pulse irradiation. On the other hand, the developments of modified structures were observed after multiple pulse irradiations on the Au and Cu surfaces. On the Si surface, deep holes, that seemed to be molten structures induced by the accumulation of multiple pulse irradiations, were found. Therefore, it is concluded that the SXRL pulse irradiations of various material surfaces cause different types of surface modifications, and the changes in the surface behaviors are attributed to the differences in the elemental properties of each materials, such as the melting point and the attenuation length of x-rays.