Composition gradient effects on strain relaxation in Sr-doped LaMnO3 epitaxial thin films

The authors report on a novel method to fabricate Sr-doped composition gradient epitaxial La1-xSrxMnO3 thin films by radio frequency magnetron sputtering. Biaxially strained epitaxial La1-xSrxMnO3 thin films were grown on (001) LaAlO3 substrates by following a cosputtering procedure from LaMnO3 and La0.67Sr0.33MnO3 targets. Three depositions were conducted by varying the substrate temperature (750 and 850 degrees C) and controlling the relative deposition rate from the two targets by varying their power rate during sputtering. The thickness of the thin films was about 20 and 30 nm for the short and long duration deposition, respectively. The films were studied by symmetric h-2h x-ray diffraction, pole figure analysis, atomic force microscopy, and x-ray photoelectron spectroscopy. Fabrication of smooth, composition gradient films of high epitaxial quality was achieved at a substrate temperature of 850 degrees C and low sputtering rate. A novel strain relaxation mechanism is also found that decreases significantly the mismatch between the film and substrate as the Sr doping level increases. The reported deposition procedure can produce new possibilities of designing nanoscale structures with cross coupled properties that may result in new materials. (C) 2015 American Vacuum Society.