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Epitaxial La 1- x Ca x MnO 3 ( x ???0.33) ultrathin films with thickness between 3 and 6?nm have been grown on (001) SrTiO 3 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. [ABSTRACT FROM AUTHOR]

We have investigated the growth of CdTe on GaAs (311)A and B structures by metalorganic vapour phase epitaxy. Growth on (311)A substrates typically enhanced twinning, whereas that on (311)B substrates retarded twin formation. Enhancement and retardation of twin formation were further correlated with growth temperatures and Te:Cd flow ratios. Twinning accounted for dual epitaxy in many of the layers. X-ray diffractometry was used to determine which CdTe layers exhibited both the tilted-(311) and the (110) orientations. Conventional and high-resolution electron microscopy was used to characterize the twins. The CdTe twins were associated with the five lowest-energy twin boundaries. The two most electrically active boundaries were the dominant incoherent twin boundary type in the layers. Twin bands varied in size, ranging from micro-twins to narrow nano-twins as thin as two atomic layers in places. [ABSTRACT FROM AUTHOR]

The decomposition of iron-nitrogen martensite (alpha) containing 5.4 at.% N, was analysed by both conventional and high-resolution transmission electron microscopy of specimens annealed at 333, 373 and 403 K. As a result of the anneals, alpha precipitates (the alpha unit cell has ideally a composition indicated by Fe[sub 16]N[sub 2]) were obtained in a ferrite (alpha) matrix ('first stage of tempering'). Because of the determined specific orientation relationship between alpha and alpha-alpha, unambiguous proof for extensive (011)-type twinning in the original martensite was obtained. The crystallography at and near the original (011)[sub alpha] twin boundary, after the decomposition alpha alpha + alpha was scrutinized. After decomposition three types of interface originated from the original (011)[sub alpha] twin boundary: alpha [sub T1]-alpha [sub T2], alpha[sub T1]-alpha[sub T2] and alpha[sub T2]-alpha[sub T2], where T1 and T2 denote the original alpha crystals constituting the twin. It followed that the local lattice orientations of alpha and alpha at or near the T1-T2 interface were dominated by the intrinsic precipitation process as observed in untwinned martensite, which led to particular clockwise and anticlockwise rotations of the alpha and alpha lattices, with respect to the parent alpha', in T1 and vice versa in T2. While the alpha[sub T1]-alpha[sub T2] and alpha [sub T1]-alpha [sub T2] interfaces remained largely at the T1- T2 interface, the alpha [sub T1]-alpha[sub T2] interface was tilted away from this interface to minimize the alpha"-alpha misfit strain energy. The misfit at the alpha[sub T1]-alpha[sub T2] and alpha [sub T1]-alpha[sub T2] interfaces was largely accommodated elastically (occasionally misfit dislocations were also present). The misfit at the alpha"[sub T1]-alpha"[sub T2] interface was accommodated by a change in orientation of the (001)[sub alpha"] lattice planes in both alpha"[sub T1] and alpha"[sub T2] near the T1-T2 interface. [ABSTRACT FROM AUTHOR]

Very thin films (less than 20 nm) of La[sub 0.73]Ca[sub 0.27]MnO[sub 3] on SrTiO[sub 3] substrates exhibit properties quite different from the bulk; they are ferromagnetic insulators instead of ferromagnetic metals. Electron microscopy shows that such thin films are perfectly smooth, single phase and crystalline, as are thicker films but that they have a structure (imposed by the lattice matching with the substrate) which is different from that of the bulk or thick films (much greater than 20 nm). The main features of this structure are a Jahn-Teller distortion of the MnO[sub 6] octahedra (not present in the bulk) and tilts of the MnO[sub 6] octahedra (different from the bulk). [ABSTRACT FROM AUTHOR]

We report the effects of biaxial strain on the charge ordering temperature Tco of the mixed-valent manganite perovskite oxide Pr0.5Ca0.5MnO3. Thin films were grown on SrTiO3, which has a 1.3% larger in-plane lattice parameter. Other substrates were used for comparison. Transport measurements combined with data from electron microscopy show that Tco is considerably enhanced. At thicknesses of the order of 10 nm, where the films are fully strained, Tco is above 320 K, more than 70 K above the bulk value of 250 K, while around 50 nm, where relaxation has set in, the enhancement is around 40 K. The bulk value is only reached at a thickness of about 150 nm. [ABSTRACT FROM AUTHOR]

We have investigated the properties of interfaces between LaAlO3 films grown on SrTiO3 substrates singly terminated by TiO2. We used RF sputtering in a high-pressure oxygen atmosphere. The films are smooth, with flat surfaces. Transmission electron microscopy shows sharp and continuous interfaces with some slight intermixing. The elemental ratio of La to Al, measured by the energy dispersive X-ray technique, is found to be 1.07. Importantly, we find these interfaces to be non-conducting, indicating that the sputtered interface is not electronically reconstructed in the way reported for films grown by pulsed laser deposition because of the different interplays among stoichiometry, mixing, and oxygen vacancies. [ABSTRACT FROM AUTHOR]