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We report on a Raman study of the phonon spectrum of La 0.7Sr0.3MnO3 thin films epitaxially grown on LaAlO3. The spectrum, as a function of film thickness d, does not change over the 1000–100 Å range, whereas a strong hardening of the phonon frequencies of both bending and stretching modes is apparent in ultra-thin films (d<100 Å) where substrate-induced effects are remarkable. This behaviour, which appears to be related with the measured d-dependence of the insulator-to-metal transition temperature, is ascribed to co-operative effects of MnO6 octahedra rotation and charge-localization. Raman spectroscopy proves to be a simple and powerful tool to monitor subtle structural modifications hardly detectable with conventional diffraction techniques in ultra-thin films. [ABSTRACT FROM AUTHOR]

Structural investigation using X-ray synchrotron radiation has been performed on SrRuO3/SrTiO3/SrRuO3 epitaxial heterostructures, with each constituent layer a few unit cell thick grown on (001) SrTiO3 substrate. Detailed information on the evolution of the in-plane lattice structure has been obtained, in these heterostructures, by grazing incidence diffraction measurements. The samples have been grown by low-pressure pulsed laser deposition. Under our deposition conditions, SrRuO3 layers grow with an elongated cell perpendicular to the substrate surface. The in-plane pseudocubic lattice parameters do not match the in-plane square SrTiO3 structure even in the case of very thin SrRuO3 layers. Such a distortion was found to decrease with increasing the thickness of the SrTiO3 barrier layer. [ABSTRACT FROM AUTHOR]

Presents the results of a study on the infrared phonons in the La0.7Sr0.3MnO3 manganite using reflectance measurements on epitaxial films. Relationship between the manganite phonon spectrum and the substrate and film thickness; Role of the thick films measurements in the determination of line profile and the peak-frequency of the bending and stretching of phonons.

In this report we demonstrate that high quality epitaxial heterostructures, based on metallic SrRuO3 and insulating SrTiO3 individual blocks a few unit cells thick, can be grown in a purely 2D, layer-by-layer mode, using pulsed laser deposition with in situ reflection high energy electron diffraction (RHEED) diagnostics. The thickness of each constituent block can be controlled at the level of a single unit cell. A detailed investigation carried out at the synchrotron facility, ESRF, by various X-ray techniques has demonstrated that each intensity oscillation of the RHEED specular spot corresponds strictly to the growth of a single perovskite unit cell, either SrRuO3 or SrTiO3. Furthermore, we show that, in these structures, the interfaces between the different constituent blocks are very sharp with a roughness of only one unit cell. [ABSTRACT FROM AUTHOR]