  All carbon materials, e.g., amorphous carbon (a-C) coatings and C60 fullerene
thin films, play an important role in short-wavelength free-electron laser
(FEL) research motivated by FEL optics development and prospective
nanotechnology applications. Responses of a-C and C60 layers to the extreme
ultraviolet (SPring-8 Compact SASE Source in Japan) and soft x-ray
(free-electron laser in Hamburg) free-electron laser radiation are investigated
by Raman spectroscopy, differential interference contrast, and atomic force
microscopy. A remarkable difference in the behavior of covalent (a-C) and
molecular (C60) carbonaceous solids is demonstrated under these irradiation
conditions. Low thresholds for ablation of a fullerene crystal (estimated to be
around 0.15 eV/atom for C60 vs 0.9 eV/atom for a-C in terms of the absorbed
dose) are caused by a low cohesive energy of fullerene crystals. An efficient
mechanism of the removal of intact C60 molecules from the irradiated crystal
due to Coulomb repulsion of fullerene-cage cation radicals formed by the
ionizing radiation is revealed by a detailed modeling.
