Low-dimensional Functional Oxide Materials Of Transmission Electron Microscopy Study

In this paper, microstructure and physical properties of Bi0.4Ca0.6MnO3epitaxial film are investigated by high-resolution transmission electron microscopy (HRTEM).The whole thesis consists of four chapters.In chapter1,the physical properties of perovskite manganites, research progress of the epitaxial films and preparation method of cross-sectional TEM specimen are generally given. The physical properties of manganites including crystal structure, lattice distortions, the strain in the epitaxial films and charge ordering are introduced. In the end, we simply introduce the preparation method of the transmission electron microscopy (TEM) specimen.In chapter2, the growth mode of Bio.4Cao.6Mn03film has been studied and the strain in the films is discussed in detail. The epitaxial films with different thicknesses are fabricated by the pulsed laser deposition technique. TEM is employed to investigate the microstructure of the Bi0.4Ca0.6MnO3epitaxial films with different thickness. The Bi0.4Ca0.6MnO3epitaxial films exhibit an island growth mode, and the morphology of the films depends on the strain states. For the10nm-thick films, the morphology is more like waves. For the40nm-thick films, the waves are broadened. When the film thickness reaches110nm, the island morphology disappears.In chapter3, the effect of film thickness to the lattice mismatch is investigated, and the effect of film thickness on the interface is discussed in detail. Dislocations both perpendicular and parallel to the interface have been observed in the110nm film. The dislocation perpendicular to the interface is caused by lattice mismatch between film and substrate. The dislocation parallel to the interface is caused by the surface roughness of the substrate.In chapter4, TEM with a low temperature sample stage is used to investigate the charge ordering behaviours in the Bi0.4Ca0.6MnO3epitaxial film. With the increase of the film thickness, the films have undergone structural transformations, i.e., from no modulation (t<100nm) to a localized incommensurate modulation (t=110nm), and further to a commensurate modulation (t=200nm).