The phase transformation dynamics induced in Ge2Sb2Te5 films by picosecond laser pulses were studied using real-time reflectivity measurements with subnanosecond resolution. Evidence was found that the thermal diffusivity of the substrate plays a crucial role in determining the ability of the films to crystallize and amorphize. A film/substrate configuration with optimized heat flow conditions for ultrafast phase cycling with picosecond laser pulses was designed and produced. In this system, we achieved reversible phase transformations with large optical contrast (>20%) using single laser pulses with a duration of 30 ps within well-defined fluence windows. The amorphization (writing) process is completed within less than 1 ns, whereas crystallization (erasing) needs approximately 13 ns to be completed.

In this work we report on the competition between growth, implantation, and sputtering effects during the production of metal nanoparticles ͑NPs͒ by pulsed laser deposition. The production sequence involves first the deposition of an amorphous ͑a-͒Al 2 O 3 layer onto which gold NPs are produced. They are subsequently covered by a-Al 2 O 3 and this sequence is repeated five times. The resulting nanocomposite films have metal contents per layer in a broad range: 1 -9 ϫ 10 15 at cm −2 . The results clearly show the formation of two NP layers per layer of gold deposited, the deepest one consisting of NPs produced by metal implanted into the a-Al 2 O 3 layer, which is acting as a substrate, and the other one consisting of NPs grown on the a-Al 2 O 3 surface. The high kinetic energy of a significant fraction of the Au species present in the plasma and the high fluxes ͑1016 -10 18 at cm −2 s −1 ͒ at the substrate plays an essential role in the nucleation and growth of the NPs. The competition between surface growth and sputtering at high fluence induces a self-regulation of the NP dimensions that narrows the size distributions.

Thin films consisting of layers of Ag nanocrystals (NCs) embedded in amorphous Al 2 O 3 were grown by pulsed laser deposition. High-resolution electron microscopy was used to characterize the structure of the films. The growth kinetics of the NCs were studied by varying the Ag content of the films between 0.8 and 12.4 × 10 15 atoms cm −2 which produced NCs with average diameters of between 1.1 and 9.6 nm. At low Ag content the NCs have a spherical in-plane shape with a narrow size distribution but they become more elongated with a broader size distribution as the Ag content increases due to coarsening and coalescence of the NCs. Underneath each layer of NCs there is a continuous layer of what is believed to be Ag implanted into the amorphous Al 2 O 3 due to the high kinetic energy, of the order of 100 eV, of the Ag species produced during laser ablation.

Phase transformations of crystalline Ge 2 Sb 2 Te 5 films upon pulsed laser irradiation have been studied using in situ reflectivity measurements with temporal resolution. Two different configurations allowed point probing with nanosecond temporal resolution and imaging with subpicosecond temporal and micrometer spatial resolution. The role of the pulse duration and laser fluence on the dynamics of the phase change and the degree of amorphization is discussed. Several advantageous features of femtosecond compared to nanosecond laser-induced amorphization are identified. Moreover, a high-resolution study of the amorphization dynamics reveals the onset of amorphization at moderate fluences to occur within ϳ100 ps after arrival of the laser pulse. At high fluences, amorphization occurs after ϳ430 ps and the molten phase is characterized by an anomalously low reflectivity value, indicative of a state of extreme supercooling.

Optical and vibrational properties of novel self-assembled silver nanocolumns are studied experimentally and theoretically. The split of the surface plasmon resonance into transverse and longitudinal modes verifies the one-dimensional character of the nanocolumns. In this work, we have identified the acoustic vibration modes of the nanocolumns using Raman scattering, as spheroid-like modes (l = 2, m = +/-2) involving vibrations of the nanocolumns along their minor axes and the existence of surface plasmon-vibration coupling mechanisms.