|Title||Amorphous to crystalline phase transition in carbon induced by intense femtosecond x-ray free-electron laser pulses|
|Publication Type||Journal Article|
|Year of Publication||2012|
|Authors||J. Gaudin, O. Peyrusse, J. Chalupsky, M. Toufarova, L. Vysin, V. Hajkova, R. Sobierajski, T. Burian, D S. Farahani, A. Graf, M. Amati, L. Gregoratti, S.P Hau-Riege, G. Hoffmann, L. Juha, J. Krzywinski, R.A London, S. Moeller, H. Sinn, S. Schorb, M. Stormer, T. Tschentscher, V. Vorlicek, H. Vu, J. Bozek, C. Bostedt|
|Journal||Physical Review B|
|Type of Article||Article|
|Keywords||DIAMOND-LIKE CARBON, DYNAMICS, films, GRAPHITE, PLASMA, SPECTRA, SPECTROSCOPY|
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 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 x 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.
|Alternate Title||Phys. Rev. B|
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