Amorphous to crystalline phase transition in carbon induced by intense femtosecond x-ray free-electron laser pulses

J. Gaudin, O. Peyrusse, J. Chalupský, M. Toufarová, L. Vyšín, V. Hájková, R. Sobierajski, T. Burian, Sh. Dastjani-Farahani, A. Graf, M. Amati, L. Gregoratti (+14 others)
2012 Physical Review B  
We present the results of an experiment where amorphous carbon undergoes a phase transition induced by femtosecond 830 eV x-ray free-electron laser pulses. The phase transition threshold fluence is found to be 282 ± 11 mJ/cm 2 . Atomic force microscopy, photoelectron microscopy, and micro-Raman spectroscopy give experimental evidence for the phase transition in terms of a volume expansion, graphitization, and change of local order of the irradiated sample area. The interaction is modeled by an
more » ... n is modeled by an accurate time-dependent treatment of the ionization dynamics coupled to a two-temperature model. At the phase transition fluence threshold the free-electron density N e is found to be at maximum 9 × 10 20 cm −3 while the ion (atom) temperature is found to be 1050 K, e.g., above the crystallization activation temperature reported in the literature. This low ionization rate and high atom temperature suggest a thermally activated phase transition.
doi:10.1103/physrevb.86.024103 fatcat:ftj2kvlumzcxvb5dwjqc2gnhje