We have studied the plasma induced at the surface of a titanium target following irradiation with femtosecond and nanosecond laser pulses. Time-resolved imaging and spectroscopic measurements allowed us to evidence some features specific to the femtosecond-laser-induced plasma. In this ultrashort interaction regime, we could discriminate between three different velocity populations in the plasma expansion. Coulomb explosion firstly creates highly energetic Ti+ ions, which are followed by atomic neutral titanium and lastly by nanoscale titanium oxide clusters

International audienc

We have studied the structural properties of ZnO thin films grown on Al2O3 (00.1) single-crystal substrates by pulsed-laser deposition using either a femtosecond or a nanosecond laser. Although hexagonal ZnO films deposited on sapphire substrate were epitaxially grown in both cases, the crystalline quality was found to be very different: ZnO films grown with the femtosecond laser are characterized by a higher mosaicity, a smaller crystallite size, a larger content of defects but also smaller residual stresses than ZnO films obtained by nanosecond laser ablation. These differences can be explained according to the kinetic energy of the species evolved during laser ablation as deduced from plasma characterization with a charged-coupled device camera: close to 1 KeV in the femtosecond regime for the population species emitted from the target with the highest velocity, versus a few hundreds of eV in the case of nanosecond pulses. The high energy species irradiation associated with a femtosecond laser is likely to induce a large structural disorder together with stress relaxation during ZnO films growth.

ZnO thin films have been grown on various substrates by femtosecond pulsed-laser deposition. According to optical microscopy and atomic force microscopy analyses, the production of droplets is not significant using femtosecond pulses. Smooth, dense, stoichiometric, crystalline, and textured hexagonal ZnO films are epitaxially grown on (0001) sapphire at 700 °C with an in-plane epitaxial relationship corresponding to a 30° rotation of the ZnO basal plane with respect to the sapphire. Nevertheless, channeling experiments and rocking curve measurements show that the crystalline quality is not as good as that obtained with nanosecond pulses.

Crystalline erbium(Er)-doped zinc oxide thin films have been grown by pulsed-laser deposition and were analyzed by the complementary use of Rutherford backscattering spectroscopy, x-ray diffraction analysis, atomic force microscopy, and photoluminescence. The composition, structure, and surface morphology of films were studied, as a function of the growth conditions (temperature from 300 °C to 750 °C and oxygen pressure from 10−6 to 0.5 mbar) and Er-doping rate, and were correlated to the emission spectroscopy of Er in the infrared domain. While these studies lead to the determination of optimal conditions for the growth of high crystalline quality films, results of photoluminescence experiments show that the insertion of Er ions in the ZnO matrix does not follow a simple pattern. The Er ions are incorporated from two pathways, one population is found inside the crystallites and another one at the grain boundaries, as a consequence of the differences in valence and ionic radius of Zn and Er.

International audienc

No abstract

No abstract