Laser ablation induced formation of nanoparticles and nanocrystal networks

Using experimental data on morphology of nanophase materials prepared by pu lsed laser ablation in an inert gas atmosphere, we present a phenomenologic al description of their condensation process. According to our idea, in hig h enough background pressure a shock wave is initiated by collisions betwee n gas and target atoms, which slows down and spatially confines the plume, while it is effectively cooled by further collisions. Thus, the plume becom es highly supersaturated and the condensed phase of the target material sta rts to develop via homogeneous nucleation. Later on, still in a very limite d volume, nanoparticles grow via complete or incomplete coalescence forming compact objects or large networks. The pressure threshold for gas phase co ndensation is intimately related to the collisional energy loss characteris tics of the particular,gas-target combination as well as to the thermophysi cal properties of the target. (C) 2000 Elsevier Science B.V, All rights res erved.