Effects of thickness on the cation segregation in epitaxial (001) and (110) La2/3Ca1/3MnO3 thin films

Electron-energy-loss spectroscopy is used to map composition and electronic states in epitaxial La2/3Ca1/3MnO3 (LCMO) films of various thicknesses grown on SrTiO3 (001) and (110) substrates. For relatively thick films (≥20 nm), epitaxial tensile strain in (001) films promotes a compositional La/Ca gradient across the film thickness, being the interface La rich, while the relaxed (110) films are chemically homogeneous. In contrast, much thinner (001) and (110) LCMO films display a different La/Ca distribution, being La rich at the free surface. The observed distinct thickness-dependent composition gradient behavior reflects a balance between strain-induced elastic energy minimization and kinetic effects during growth.