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Abstract
Epitaxial La1−x Ca x MnO3 (x ≅ 0.33) ultrathin films with thickness between 3 and 6 nm have been grown on (001) SrTiO3 substrates by sputter deposition. The films do not exhibit an insulator-metal transition as a function of temperature, which is normal in thicker films. High-resolution transmission electron microscopy and electron diffraction were used to investigate the crystal structure. It was found that the films grow coherently on the substrates and are perfectly crystalline. Their crystal structure was determined to be a body-centred orthorhombic structure with space group Imma, instead of the orthorhombic Pnma bulk structure. This structure change is probably responsible for the insulating property of the films.
Acknowledgement
This work was part of the research program of the Stichting voor Fundamenteel Onderzoek der Materie (FOM), which is financially supported by NWO.