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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]

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.