Expansion flow and cluster distributions originating from ultrafast-laser-induced fragmentation of thin metal films: A molecular-dynamics study

Using molecular-dynamics simulation, we study the fragmentation patterns of ultrathin metal films as a function of the initial energization. The energization is assumed to occur instantaneously. Above the threshold for fragmentation, a homogeneous expansion of the exploding film is observed, in which a mixture of clusters of all sizes is found. The internal temperature of the clusters is constant, independent of space, time, and cluster size. The cluster size distribution can be characterized for small energizations as a biexponential distribution, but is better represented for larger energizations by a power law in cluster size m,proportional to m(-alpha), with an exponent alpha congruent to 2.8-3.1.