Lattice-mismatch Strain Effects in Electron-Doped Calcium Manganese Oxide Thin Films

Electron-doped Calcium Manganese Oxide (CaMnO$_{3-\delta}$) thin films are of interest for use as photocatalysts and fuel cell electrodes in renewable energy applications. Oxygen stoichiometry of the films is a key parameter for the functionality in these applications. Currently, we are investigating the properties of (CaMnO$_{3-\delta}$) films grown by pulsed laser deposition. The thin films are epitaxially grown on LaAlO$_{3}$ and SrTiO$_{3}$ substrates. Both of these substrates have larger in-plane lattice parameters than CaMnO$_{3-\delta}$, which leads to bi-axial tensile strain in the thin films. We have characterized the thickness dependence of structural, electrical, and morphological properties of these films using high resolution x-ray diffraction, temperature dependent electrical resistivity measurements, and atomic force microscopy. The thickness dependence is characteristically different from what has been preciously observed in thin films of hole-doped manganites. Our results suggest that coupling between tensile strain and oxygen deficiency affect the electrical and structural properties of the material.