Particulates-free Ta thin films obtained by pulsed laser deposition: the role of a second laser in the laser-induced plasma heating

The presence of various types of particulates on the surface of the thin films deposited by pulsed laser deposition (PLD) is a strong limitation in key technological applications of this method. We investigated the morphology of the Ta thin films obtained by a two laser system technique. The first UV laser was used for the target ablation, and the second IR laser, propagating parallel with the target surface, intercepted the particulates present in the ablation plasma. We chose the second laser wavelength in IR because of its much higher absorption by plasma and liquid particles. The particulates density on the surface of the films was studied as a function of the time delay between the UV and IR laser pulses. Depending on the ablating laser experimental parameters, we succeeded to obtain a delay time regime 10–300 μs for which completely particulates-free films were deposited. For these delay values, the second laser intercepted the slow component of the ablation plasma consisting on micrometer sized particulates with propagation velocity within the range of 103 to 104 cm/s.