Pulsed laser deposition: From basic processes to film deposition

The production of thin films by pulsed laser deposition (PLD) has become a standard method, even though many of the basic processes are not known in detail. The key quantities are the ablation rate (yield) and the angular distribution of the ablated particles. The starting point for this study is the comparatively simple case of one-component metals rather than metal oxides which in the past have been comprehensively studied. The ablation rate depends primarily on the thermal properties of the metal, in such a way that a low cohesive energy leads to a high ablation rate. The angular distribution of the ablated atoms is important for the uniformity of the film thickness as well as the deposition rate on a substrate. However, if the ablation takes place in a background gas, the angular distribution of collected ablated atoms becomes comparatively broad. Combined diagnostic measurements of deposition rates and ion time-of-flight (TOF) signals have been used to study the dynamics of a laser ablation plume in background gases. The angular distribution and the TOF signals exhibit three separate regimes with increasing pressure, a vacuum-like regime, a transition regime with increasing plume broadening and splitting of the ion signal, and at the highest pressures a diffusion-like regime with a broad angular distribution.