Laser ablation induced formation of nanoparticles and nanocrystal networks

Using experimental data on morphology of nanophase materials prepared by pulsed laser ablation in an inert gas atmosphere, we present a phenomenological description of their condensation process. According to our idea, in high enough background pressure a shock wave is initiated by collisions between gas and target atoms, which slows down and spatially confines the plume, while it is effectively cooled by further collisions. Thus, the plume becomes highly supersaturated and the condensed phase of the target material starts to develop via homogeneous nucleation. Later on, still in a very limited volume, nanoparticles grow via complete or incomplete coalescence forming compact objects or large networks. The pressure threshold for gas phase condensation is intimately related to the collisional energy loss characteristics of the particular,gas-target combination as well as to the thermophysical properties of the target. (C) 2000 Elsevier Science B.V, All rights reserved.