At low fluences, the [Sr]/[Ti] ratio of laser deposited SrTiO3 films appears to be a function of the laser fluence. The deviation from stoichiometry is remarkably constant in time. From an analysis of both the composition of the film and the irradiated target, we deduce a volume-diffusion-assisted preferential ablation process. At high fluences (above 1.3 J/cm2), stoichiometric SrTiO3 films are obtained. This is not due to a change in ablation mechanism, but follows from the fact that at 1.3 J/cm2 the calculated diffusion length of Sr within the irradiated target, becomes of the order of the ablation rate per shot.@en

YBa₂Cu₃O_7-δ films on SrTiO₃ are characterized by a network of anti-phase boundaries (APB's), protruding from the interface to the film surface. We propose that the island morphology of these films is to a large extent determined by this network. At APB-outcrops deep trenches form which separate the growth islands. At the cross-section of three APB's deep holes are formed. It is found that the growth island size can be increased by increasing the substrate temperature or the oxygen pressure during growth.

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Investigating the epitaxial nature of YBa2Cu3O7-δ films on NdGaO3 (001) by Rutherford backscattering (RBS) and X-ray diffraction (XRD) texture measurements we find that the films are almost single crystalline, in the sense that the a, b and c axes are uniquely defined with respect to those of NdGaO3. The crystalline perfection is, however, not reflected in the electrical properties of the films. Although we measure a Tc of 89.7 K, we did not observe the expected anisotropy in the resistivity. We interpret this to be due to Ga diffusion from the substrate into the film, which effectively blocks the chain conductivity.@en

We report on the magnetic and transport properties of thin films of La0.67Ca0.33MnO3 as a function of annealing temperature, substrate material and film thickness. The films were sputtered from a stoichiometric target with the same nominal composition and were grown epitaxially on SrTiO3 and LaAlO3 substrates. We find a clear correlation between the ferromagnetic ordering temperature TM and the magnitude of the magnetoresistance ratio (MR ratio). Also, TM appears to be extremely sensitive to the preparation conditions: within the one composition investigated, TM could be made to vary between 125 K and 255 K.@en

High quality twin-free c-axis oriented YBa2Cu3O7-δ films were grown by pulsed laser deposition on NdGaO3. We find resistive anisotropies between 1 < ρa/ ρb < 1.6. The resistive anisotropy above Tc appears to be correlated to the anisotropy in the critical current below Tc. The normal state properties of the chains along b seem to have a significant influence on the superconducting properties of YBa2Cu3O7-δ.@en

We provide evidence that non-stoichiometric ablation of YBa₂Cu₃O_7-δ at low fluences is due to a phase separation of the target surface. On the other hand, in SrTiO₃ we find at low fluences evidence for preferential ablation which is assisted by volume-diffusion. As a result, the Sr/Ti ratio of the ablated films can be tuned by choosing the appropriate fluence.

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Projection optics is a means to reduce the spatial energy density variations on the target during laser ablation. Using projection optics to study the interaction between a spatially uniform 248 nm excimer laser beam and a YBa2Cu3O6+x target we observe a well-defined threshold fluence of 1.0 J/cm2. Below this threshold non-stoichiometric ablation results in an dramatic change in target morphology and in a decay of the ablation rate. Above this threshold the stoichiometry of the target is conserved. The roughness of the deposited films increases along with the increase in roughness of the target above the threshold. Thus it is clear that in order to obtain flat stoichiometric films one should use a narrow fluence window just above the threshold.@en

Using projection optics we made a detailed study of the interaction of a spatially uniform 248 nm excimer laser beam and a 99% dense YBa 2Cu3O6+x target. Below a threshold fluence of 1 J/cm2 the roughness of the irradiated target increases dramatically due to non-stoichiometric ablation. The overall target surface composition becomes increasingly Y rich and Cu poor, while the opposite is found for the corresponding ablated thin films. Above the threshold fluence the composition of the ablated target surface is conserved. As a result of the energy homogeneity of the laser beam obtained by means of projection optics, the optimization of the deposition parameters has been improved leading to the reproducible fabrication of flat, stoichiometric YBa2Cu3O7 films with Tc0's over 91 K.@en

The dynamical relaxation rate Q dln js/dln(dB/dt) where js is the current induced in a superconductor when the external field is swept at a rate dB/dt, has been measured in YBa2Cu3O7 and Y2Ba4Cu8O16 films of 100 nm and 180 nm thickness as a function of magnetic field at temperatures between 2 K and Tc. The data show i) a non zero relaxation at low T due to quantum creep, ii) a plateau between 15 and ∼ 50 K and iii) a divergence when T approaches the irreversibility line. The data are analyzed within the collective pinning model. At low temperatures it is shown that both js and Q are influenced by quantum creep.@en