Plume dynamics during film and nanoparticles deposition by pulsed laser ablation

The gas dynamics of pulsed laser ablation of silicon target in the helium as ambient is investigated via direct simulation Monte Carlo method with a real physical scale of target-substrate configuration. A shock driven process is clearly observed. It is shown that the interaction of the shock front with the target surface and the vapor front induce significant backward flux of ablated particles and oscillating behavior of vapor front. A confined layer mixed with high density Si and He atoms is formed around the contact front. Its behavior is important to the nanoparticle formation and deposition. (C) 2002 Elsevier Science B.V. All rights reserved.