Samples of B4C, amorphous C, chemical-vapor-deposition-diamond C, Si, and SiC were exposed to single 25fs long pulses of 32.5nm free-electron-laser radiation at fluences of up to 2.2Jcm2. The samples were chosen as candidate materials for x-ray free-electron-laser optics. It was found that the threshold for surface damage is on the order of the fluence required for thermal melting. For larger fluences, the crater depths correspond to temperatures on the order of the critical temperature, suggesting that the craters are formed by two-phase vaporization.

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