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We report on the growth of cuprous oxide on MgO(001) by plasma-assisted molecular beam epitaxy. An increased copper to oxygen ratio enhances the cube-on-cube growth of the Cu 2 O crystallites compared to the Cu 2 O(110)||MgO(100) oriented crystallites. This correlates with the occurrence of a (3√2×√2)R45° surface reconstruction observed during growth. This reconstruction is known to be unstable under oxygen-rich conditions and stabilizes the Cu 2 O(001) surface compared to the Cu 2 O(110) surface for higher copper to oxygen ratios enhancing cube-on-cube growth. High resolution X-ray diffraction analysis of the resulting cube-on-cube Cu 2 O layers indicates partial relaxation by 39.7%. Investigations of the optical absorption and photoluminescence properties of the films reveal excitonic contributions comparable to those of single crystals. [ABSTRACT FROM AUTHOR]

Abstract: Lithium tantalate (LT) is an oxide material whose congruent composition differs from its stoichiometric composition in the Li2O–Ta2O5 binary system. Ionic species in the LT melt are segregated during crystal growth, even at the congruent composition, which leads to crystallization electromotive force (C-EMF) at the solid–liquid. On the other hand, when a compound has a stoichiometric structure at the congruent composition, such segregation does not occur. By employing a new concept of stoichiometry of a material where the activity of any constituent element could be unity, we developed a new lithium tantalate with MgO doping, cs-MgO:LT (Li2O:Ta2O5:MgO=40.8:50.0:9.2), that is stoichiometric and coincident with the congruent composition. Because of this coincidence, cs-MgO:LT does not yield C-EMF and does not show segregation during growth even for ionic species. A bulk crystal was grown from the melt of the cs-MgO:LT composition via the Czochralski (CZ) method, and it showed excellent compositional homogeneity, proved by the constant distribution of the Curie temperature throughout the crystal. [Copyright &y& Elsevier]

Electron paramagnetic resonance spectroscopy is used to characterise Mo(V) centres present on the surface of MgO(100) films grown on Mo(100) single-crystal surfaces at 600 K. The Mo(V) centres exhibiting a molydenyl group to reduce the charge imbalance with respect to the MgO lattice substitute Mg cations on regular terrace sites within the MgO(100) islands as deduced from angular-dependent measurements and spectral simulations. The observed anisotropic Zeeman and hyperfine interaction is comparable with Mo(V) centres supported on different powdered oxide surfaces such as alumina or silica. Analysis of the films grown at 300 K and subsequently annealed to elevated temperatures to improve the long-range order shows that the presence of the Mo sites on the surface is a thermally activated process. Comparison of the defect structures of the two preparation methods suggests that Mo plays a role in the relaxation of the lattice misfit between the Mo substrate and the MgO film. [ABSTRACT FROM PUBLISHER]

We report results of high-resolution sputter depth profiling of an alternating MgO/ZnO nanolayer stack grown by atomic layer deposition (ALD) of 5.5 nm per layer. We used an improved dual beam time-of-flight secondary ion mass spectrometer to measure 24Mg+ and 64Zn+ intensities as a function of sample depth. Analysis of depth profiles by the mixing-roughness-information model yields a 1.5 nm nanolayer interfacial roughness within the MgO/ZnO multilayer. This finding was cross-validated using specular x-ray reflectivity. Such an analysis further suggested that the 1.5 nm roughness corresponds to native/jig-sawed interfacial roughness rather than interfacial interdiffusion during the ALD growth. [ABSTRACT FROM AUTHOR]

Abstract: Transition metal ions (Mn2+, Cr3+, Fe2+/3+, V2+) as substitutional impurities in cubic crystals play an important role due to their influence on the magneto-optical properties of the virgin crystals. The optical and magnetic properties of commercial MgO(001) single crystals were investigated. The PL spectra of 3d impurity ions (Cr3+ and V2+) show narrow zero phonon lines with decay times in the range of milliseconds and a broad multiphonon sideband decaying in microseconds. The EPR study exhibits hyperfine components corresponding to Mn atoms and to V atoms located in orthorhombic symmetry. The intensity change of the EPR and PL spectra as well as the variation of the decay time with temperature can be explained by electron-spin lattice relaxation due to the Raman process. [Copyright &y& Elsevier]

Abstract: A batch production for fabrication of LREBa2Cu3O y (LRE: Sm, Gd, NEG) “LRE-123” pellets are developed in air and Ar-1% O2 using a novel thin film Nd-123 seeds grown on MgO crystals. The SEM and XRD results conformed that the quality and orientation of the seed crystals are excellent. On the other hand, new seeds can withstand temperatures >1100°C, as a result, the cold seeding process was applied even to grow Sm-123 material in Air. The trapped field observed in the best 45mm single-grain puck of Gd-123 was in the range of 1.35T and 0.35T at 77.3K and 87.3K, respectively. The average trapped field at 77.3K in the 24mm diameter NEG-123 samples batch lies between 0.9 and 1T. The maximum trapped field of 1.2T was recorded at the sample surface. Further, the maximum trapped field of 0.23T at 77K was recorded in a sample with 16mm diameter of Sm-123 with 3mol% BaO2 addition. As a result we made more then 130 single grain pucks within a couple of months. Taking advantage of the single grain batch processed material, we constructed self-made chilled levitation disk, which was used on the open day of railway technical research Institute. More then 150 children stood on the levitation disk and revel the experience of levitation. The present results prove that a high-performance good-quality class of LREBa2Cu3O y material can be made by using a novel thin film Nd-123 seeds. [Copyright &y& Elsevier]

Abstract: MgO nanobelts were obtained by the decomposition of magnesium nitrate in a direct current arc plasma jet chemical vapor deposition process, with a Mo substrate at 950°C for different durations. The products formed in the first 0.5min were nanobelts, some of which possessed spherical particles on tips of nanobelts, forming “tadpole-like” nanostructures. When the reaction time was extended to 1min, nanobelts become longer although spherical particles were still observed. When the reaction time was 3min, nanobelts became even longer, and no spherical particles were observed. Extending the reaction time to 5min significantly widened the nanobelts, with widths ranging from 10 to 100nm. The MgO nanobelt growth occurred along the 〈100〉 and the 〈111〉 axes. The growth mechanism of the MgO nanobelts was a combination of axial VLS and side VS growth. Nanobelts exhibited strong ultraviolet–blue photoluminescence emission under excitation at 350nm. [Copyright &y& Elsevier]

We prepared a polycrystalline sample of orthorhombic La0.7Ca0.2Sr0.1MnO3 and then investigated its magnetic properties. Detailed studies and analyses in the vicinity of the ferromagnetic (FM)-paramagnetic phase-transition temperature prove the sample undergoing a second-order phase transition, where variations of the saturation magnetization and the initial susceptibility versus temperature obey asymptotic relations. Basing on the modified Arrott plot, we have determined the critical parameters (TC, β, γ, and δ) in the two characteristic regions of low- and high-magnetic fields, and in the cases of no-subtracting and subtracting the demagnetization field (Hd). The experimental results reveal that values of the critical parameters depend remarkably on analysis routes of isothermal-magnetization data. Intrinsically, β keeps close to the value expected for the 3D Heisenberg ferromagnets with ferromagnetic short-range interactions, while γ is close to the value of the mean-field theory. These results are different from those reported previously on a La0.7Ca0.2Sr0.1MnO3 single crystal exhibiting a tri-critical point. The effects related to grain boundaries and isotropic properties existing in the polycrystalline sample are assigned to cause such the phenomena. Particularly, around TC, the magnetic-entropy change reaches a maximum value of 4.3 J kg-1 K-1 under an applied field of 30 kOe, which corresponds to a relative cooling power ∼150 J/kg suitable for magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]