Gas Phase Reaction Dynamics in Pulsed Laser Deposition

Pulsed laser deposition (PLD) has proved to be an outstanding technique for the deposition of complex oxide thin films due to its ability to congruently transfer the target composition to the deposited film. The deposition of many oxides is usually conducted using a pulsed KrF laser (λ= 248 nm corresponding to 4.99 eV/photon) with a pulse length of a few 10 ns in an O₂ background gas. The wavelength combined with the pulse length results in a plasma plume consisting largely of monoatomic plasma species (excited, ion, and neutral species plus electrons). The background gas moderates the kinetic energy of the expanding plume species, forming additional ions and excited state species. In addition, O₂ can act as a reactive background gas adjusting the oxidation of the ablated species and of the film. The gas-phase reaction dynamics and kinetics in a laser induced plasma are very much dependent on the interactions of the laser ablated target material and the background gas. As ions from the ablation process have a wide kinetic energy range, the question of interest is to determine the favourable kinetic energy window at which plasma species react/interact with the background gas molecules to form neutral and ionic metal-oxygen (MO) species.