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.

We analyze the limitations imposed by sample absorption on the determination of the nonlinear refractive index by the Z-scan technique. By using a nanostructured thin film consisting of Cu nanocrystals embedded in a dielectric Al 2 O 3 matrix as an example, we show that thermo-optical effects appearing when linear absorption is significant can be strongly misleading in the interpretation of the results of a Z scan. Even though this effect is not new, the widespread use of the Z-scan technique during the past several years makes it necessary to analyze explicitly the conditions under which the technique can be reliably applied and when more sophisticated techniques should be used instead. We discuss the contributions to the signal under different experimental conditions, several diagnostic techniques to discriminate true nonlinear effects from thermally induced phenomena, and different methods to reduce the thermal contribution.

Erbium doped Al 2 O 3 films with concentrations up to 6ϫ10 20 Er cm Ϫ3 have been prepared in a single step process by pulsed-laser deposition. Alternate ablation of Al 2 O 3 and Er targets has been used to control the in-depth distribution and in-plane concentration of Er 3ϩ ions independently. The characteristic Er 3ϩ photoluminescence response at 1.53 m has been studied as a function of the Er 3ϩ distribution. It is found that lifetime values can be greatly increased by increasing the Er 3ϩ-Er 3ϩ in-depth separation above 3 nm. This result can be related to a reduced Er 3ϩ-Er 3ϩ energy migration process. The in-plane Er 3ϩ concentration was increased by either increasing the number of pulses on the Er target or the laser energy density for ablation. By the latter method in-plane concentrations as high as 1.1ϫ10 14 Er cm Ϫ2 per layer ͑corresponding to 2 ϫ10 20 Er cm Ϫ3 ͒ were achieved, while keeping lifetime values as high as 6 ms. This result is explained in terms of shallow Er 3ϩ implantation during deposition.

The optical response of nanocomposite thin films formed by Cu nanoparticles (NPs) embedded in amorphous aluminium oxide (Al2O3) prepared by pulsed laser deposition (PLD) in vacuum is studied in order to investigate the possible existence of reactive processes on the Cu NPs during their covering with Al2O3. The study is performed as a function of the laser fluence on the Al2O3 target (0.6–4.6 J cm−2), while the laser fluence for Cu ablation is kept constant (1.8 J cm−2). The structural analysis of the films shows that they are formed by a high density of NPs with average dimensions in the 4.9–5.9 nm range. The optical response of the films has been followed in situ by real-time reflectivity measurements at 633 nm and after deposition by transmission measurements as a function of wavelength around the surface plasmon resonance (SPR). For low laser fluences on the Al2O3 target, the absorption spectrum is dominated by a well-defined SPR absorption band at 1.9 eV. As the laser fluence is increased, the intensity of the absorption band associated with the SPR decreases and shifts to 2.1 eV. The films deposited at low fluences contain metallic Cu NPs and, as the laser fluence increases sputtering of Cu from the NPs and mixing of the species from the Al2O3 deposition with the Cu from the NPs surface takes place. The latter process leads to the formation of an Al–Cu oxide cover on the Cu NPs. The present results provide evidence for mixing of species from the host and Cu at the surface of the NPs, and it is shown how the degree of mixing depends on the laser fluence used to ablate the Al2O3 host target.

Thermally induced transmission and reflectivity changes are investigated in thin films formed by Bi nanostructures embedded in amorphous Al2O3. The Bi nanostructures are formed by coalesced nanoparticles forming a quasi-network close to the percolation threshold. Upon heating above the Bi melting temperature (>574 K), the transmission of the film increases abruptly, up to 18% in respect to the initial value, which is related to Bi melting. Upon cooling, the high transmission state remains up to temperatures as low as 436 K, thus evidencing a wide melting–solidification hysteresis cycle. The existence of transient morphological changes within the embedded nanostructure related to the contraction of Bi upon melting seems to have a significant contribution to the large transmission contrast between the molten and solid states of the Bi nanostructures. This large contrast together with the large width of the cycle makes this nanostructured film promising for a thermally driven optical switch.