Plasma plume dynamics, rebound, and recoating of the ablation target in pulsed laser deposition

摘要

The effects of the type of background gas and pressure on the spatial distributions of plume species have been investigated by time and space resolved imaging in vacuum, 1 × 10~(-2) mbar and 1 x 10~(-1) mbar O_2 and Ar. The ablation of La_(0.4)Ca_(0.6)MnO_3 in vacuum shows dissimilar arrival times for the different neutral species and a backscattering of the impinging species from the substrate. At 1 x 10~(-2) mbar, a species-dependent plume splitting appears and preferential scattering of the lighter elements is detected generating a cation off-stoichiometry along the plume axis. In addition at 1 x 10~(-1) mbar the plume expansion in this relatively high pressure traps a portion of the background gas against the substrate holder, thereby creating a transient high local pressure with remarkable effects once the plume reaches the substrate. In an Ar background, a rebound wave is seen, which travels backwards and recoats/contaminates the target with a different composition than the original target. In O_2, in addition to the rebound, a long-lived volume of excited species is created, which consists mainly of LaO I. The rebound has important effects on the film composition and is background gas dependent. The same effects are also detected during Ag ablation and are probably valid for most target materials.