Size-dependent ultrafast ionization dynamics of nanoscale samples in intense femtosecond x-ray free-electron-laser pulses

All matter exposed to intense femtosecond x-ray pulses from the Linac Coherent Light Source free-electron laser is strongly ionized on time scales competing with the inner-shell vacancy lifetimes. We show that for nanoscale objects the environment, i.e., nanoparticle size, is an important parameter for the time-dependent ionization dynamics. The Auger lifetimes of large Ar clusters are found to be increased compared to small clusters and isolated atoms, due to delocalization of the valence electrons in the x-ray-induced nanoplasma. As a consequence, large nanometer-sized samples absorb intense femtosecond x-ray pulses less efficiently than small ones.