%0 journal article
%@ 1098-0121
%A Gaudin, J.,Peyrusse, O.,Chalupsky, J.,Toufarova, M.,Vysin, L.,Hajkova, V.,Sobierajski, R.,Burian, T.,Dastjani-Farahani, S.,Graf, A.,Amati, M.,Gregoratti, L.,Hau-Riege, S.P.,Hoffmann, G.,Juha, L.,Krzywinski, J.,London, R.A.,Moeller, S.,Sinn, H.,Schorb, S.,Stoermer, M.,Tschentscher, T.,Vorlicek, V.,Vu, H.,Bozek, J.,Bostedt, C.

%D 2012
%J Physical Review  B
%N 2
%P 024103 
%R doi:10.1103/PhysRevB.86.024103
%T Amorphous to crystalline phase transition in carbon induced by intense femtosecond x-ray free-electron laser pulses
%U https://doi.org/10.1103/PhysRevB.86.024103
2 
%X 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/cm2. 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 accurate time-dependent treatment of the ionization dynamics coupled to a two-temperature model. At the phase transition fluence threshold the free-electron density Ne is found to be at maximum 9 × 1020 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.