Nanoscale surface modifications and formation of conical structures at aluminum surface induced by single shot exposure of soft x-ray laser pulse

We irradiated the soft x-ray laser (SXRL) pulses having a wavelength of 13.9 nm, a duration time of 7 ps, and fluences of up to $27mJ/cm2$ to aluminum (Al) surface. After the irradiation process, the modified surface was observed with the visible microscope, the scanning electron microscope, and the atomic force microscope. The surface modifications caused by the SXRL pulses were clearly seen, and it was found that the conical structures having about 70–150 nm in diameters were formed under a single pulse shot. The conical structures were formed in the features with the average depth of about 40 nm, and this value was in accordance with the attenuation length of the SXRL beam for Al. However, those conical structures were deconstructed under the multiple pulse shots exposure. Thermomechanical modeling of SXRL laser interaction with Al surface, which explains nanostructure surface modification, was provided.