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Structural and physical properties of ReNiO3 (Re=Sm, Nd) nanostructured films prepared by Pulsed Laser Deposition

Ngom , Balla Diop (2010) Structural and physical properties of ReNiO3 (Re=Sm, Nd) nanostructured films prepared by Pulsed Laser Deposition. PhD thesis, University of the Western Cape.

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Using PLD, we have synthesized Sm1-xNdxNiO3 (at x=0.45) films, stabilized by epitaxial strain on Si (100) substrate and NdGaO3 (110) perovskite-type substrate. The effect of the deposition oxygen pressure and the deposition time on structural and morphological properties has been investigated. Scanning electron microscopy and atomic force microscopy suggest that the microstructure is similar at different oxygen pressures. On the other hand, the structural properties do strongly depend on the oxygen pressure and the used substrate. In each film the structure was found to be consistent with a perovskite structure with preferential planes growth and reveals a strong orientation along the orthorhombic (210) plane of the perovskite subcell for the film deposited on NdGaO3 where highly crystalline films were obtained within 15 min deposition time with a low surface roughness of 8.79 nm. Similar structure is observed on Si (100) substrate only at O2 pressure of 0.4 mbar. Resistivity measurements as a function of temperature illustrate a smooth continuous metal-insulator transition for films with only few structural defects. The surface morphology of the different samples shows a net dense film structure with several droplet populations. The nano-scaled droplets are in general spherical in shape which indicates that the laser ablation of this nickelate family is governed, to a certain extent, by a heat transfer phenomenon in the present experimental conditions. The study on plume dynamic shows that the plasma plume expansion dynamic passes from free-like to shock-like and finally reaches a complete stopping at times and distances depending on the gas pressure. It was found that the validity of the shock-wave model is restricted to a distance region which depends on the gas pressure. A drag model is a good approximation for the later plume expansion regime. An optimal target-substrate distance was predicted for each gas pressure based on the plasma plume stopping distance. This study on plasma expansion demonstrates the direct dependence of O2 pressure of the evolution of the crystalline state and surface morphology of PLD grown Sm0.55Nd0.45NiO3 films through the formation of the shock wave. On the basis of these data it has to be noticed that this estimate morphology feature where all films show a similar behavior as a function of pressure, can be related into the diffusion of the plasma species as the films were deposited at distance above the estimated stopping distance of the plasma.

Item Type:Thesis (PhD)
Subjects:Material Science > Nanostructured materials
ID Code:9619
Deposited By:Mr Saleh Khamlich
Deposited On:13 Sep 2010 12:14
Last Modified:22 Apr 2011 13:55

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