Thickness dependence of microstructure in LaCaMnO thin films

Introducing biaxial strain in doped lanthanum manganite thin films is an excellent tool to modify the electrical and transport properties systematically by controlled changes of the microstructure on an atomic scale. We deposited La2/3Ca1/3MnO3 thin films onto SrTiO3 single-crystal substrates under reproducible conditions in an optimized pulsed laser deposition process. A thickness range of 40 to 500 nm was chosen for the manganite layers to investigate the variation of the average lattice parameters with thickness using X-ray diffraction. We re-investigated the samples after annealing to determine the structural aspects of the relaxation behavior of the layers. A second set of samples was prepared with an analogous in situ annealing process. AFM was applied to examine the morphology and grain size of the layers. Due to a thermally induced strain relaxation process the thicker films show a gradual approach of the out-of-plane lattice constant to the bulk ceramic value. Further relaxation could be achieved with an annealing at 900 deg. C for 1 h. Lattice parameter changes with varying thickness and annealing processes are correlated with transport and magnetic properties