L. Cultrera

Characterization of Hastelloy thin films deposited by pulsed laser ablation

Hastelloy thin films have been deposited on carbon steel substrates at room temperature by pulsed laser ablation of bulk Hastelloy targets. Different numbers of laser pulses were used in order to obtain films of various thicknesses. Scanning electron microscopy (SEM) was used to analyze the surface morphology of the deposited films. Energy dispersion X-ray (EDX) spectroscopy and X-ray diffraction (XRD) have shown that the laser ablation process was almost congruent, and the crystallographic structure was retained in the films. In order to relate the microstructure of the film surface with its corrosion behavior, electrochemical tests in aqueous CO2 environment, such as potentiodynamic curves and linear polarization resistance, were performed. The film characteristics and their dependence on deposition parameters are presented and discussed.

Detailed studies of the plume deflection effect during long laser irradiation of solid targets

Abstract The changes of the laser ablated target morphology and the corresponding plume deflection angle have been studied. As the number of laser pulses/site increases, the target morphology changes and produces a visible deviation of the plasma plume. Scanning electron microscopy analyses of the target surface allowed us to correlate the plume deflection angle to the target roughness and, hence, to the number of laser pulses/site. The deflection effect has been observed for all the targets used (Ti, Si, Cu, Al–Sn alloy, graphite and magnetic compounds) and for whatever target surface morphology produced by laser irradiation. As earlier models explaining the origin of the plume deflection are not universal and less than ever satisfactory, we suggest a simple model that seems to be more realistic and general.

Extensive Studies of the Plume Deflection Angle During Laser Ablation of Si Target

The plume deflection effect during long laser irradiation of a Si target has been extensively studied. Two different laser ablation experiments were performed to study the plume deflection angle and the ablation rate versus the number of laser pulses/site. Scanning electron microscopy (SEM) analyses and profilometry of the Si target surface were performed to examine the continuous morphological changes produced by the laser irradiation. The roughening of the target surface strongly influenced the formation and expansion of the Si plume. Plume deflection angles higher than 30° have been observed by a digital camera. Complementary mass spectrometer measurements confirmed that the ion flux distribution is strongly oriented along the laser beam direction. In addition to laser ablation experiments, two other laser deposition experiments were performed: with the conventional configuration and with a new approach, termed frontal off-axis deposition. The new pulsed-laser deposition configuration provides much better control of uniformity and film thickness than the conventional deposition configuration.

Effects of codoping in ZnO-based semimagnetic semiconductor thin films

Single doped Zn1−xMnxO, Zn1−xFexO and codoped Zn1−x−yMnxFeyO, Zn1−x−yMnxSnyO, Zn1−x−yMnxLiyO, Zn1−x−yFexAlyO thin films were grown on sapphire and glass substrate by pulsed laser deposition and RF sputtering techniques. No secondary phases was detected from XRD analysis. Among the studied oxide films single doped with Fe and codoped with (Mn,Fe) and (Fe, Al) exhibit n-type conductivity and room temperature ferromagnetic behaviour. For the films codoped with (Mn, Sn) formation of clusters including nanowire-like structures was shown from AFM analysis. Optical and magnetooptical studies suggest of Mn, Fe, Sn and Li substitution for Zn2+ ions in ZnO lattice.