軟X線による物質アブレ一シヨン

摘要

X-ray ablation has been recently achieved using plasma soft X-ray lasers, laser plasma soft X-rays, and X-ray free electron lasers. Nanosecond laser plasma soft X-rays sources allow us to fabricate high-quality micro- and nano-structures of poly (methylmethacrylate) (PMMA), poly (dimethylsiloxane) (PDMS), and SiO_2. Even after the soft X-ray irradiation, the surfaces of these materials have the same chemical structures as those of unirradiated surfaces. We found that ablation of SiO_2 occurs more efficiently than linear optical absorption and energy accumulation to break all of the bonds in SiO_2 surfaces. Picosecond plasma soft X-ray laser sources allow us to ablate LiF crystals at a low threshold fluence. The ablation is explained in terms of spallative ablation, that is, removal of a surface layer by tensile stress induced by the short-pulse X-ray irradiation, without breaking the layer into atomic species. It should be noted that nanostructures such as nano-cones on Al surfaces can be fabricated by irradiation with the plasma soft X-ray laser light