Ultrashort Pulse PLD: A Technique for Nanofilm Fabrication

Abstract

In the present contribution the peculiarities of laser ablation are discussed with special emphasis on the differences in the mechanisms of nanoparticle formation when ablating materials with pulses of nanosecond vs. femtosecond duration. In the case of ablation using nanosecond pulses the dominating species leaving the target surface are principally atoms and ions. Cluster formation and growth mainly take place, via nucleation and condensation, from the plasma plume within the surroundings. The principal control parameter is the ambient pressure. When the major goal is not the production of colloids (either in form of an aerosol or a sol) but layer growth instead, nanostructured films can be made at pressures higher than a few pascals. On the other hand, ablation with ultrashort pulses produces a plasma plume of biphasic character: its leading edge, consisting of ionic and atomic components is followed by a spatially and temporally well separated cloud of nanoparticles. In this case nanoparticle formation is a direct consequence of the interaction of the ultrashort laser pulse with the target material. This process even works in high vacuum, which provides an additional proof for that here, contrary to nanosecond-ablation, those are the laser parameters that control the characteristics of the nanoparticles produced.