Quantitative strain analysis and growth mode of pulsed laser deposited epitaxial CoFe2O4 thin films

A microstructural investigation of epitaxial CoFe2O4 films grown by pulsed laser deposition on single crystal SrTiO3 substrates was performed. We quantitatively analysed the microscopic mechanisms for structural mismatch compensation and the mode of the film growth. X-ray diffraction revealed very low microstrain in all three crystallographic directions of the film, which together with the lattice strain is not large enough to compensate effectively for the mismatch. Quantitative high-resolution transmission electron microscopy showed that most of the compensation occurs by formation of (4 0 0) edge dislocations in the film. These dislocations are concentrated within a critical layer above which a change from layer-by-layer growth to island growth was observed. These observations closely correspond to characteristics of the Stranski–Krastanov growth mode. Atomic force microscopy studies confirmed that during the post-annealing long-range mass diffusion takes place, which facilitates the relaxation of the microstrain during this treatment.