Abstract: Er3+Yb3+ co-doped transparent glass-ceramics with varying Er/Yb content and ratio have been prepared. High quantum yields for up- and down-conversion luminescence by energy transfer from Yb3+ to Er3+ and from Er3+ to Yb3+, respectively, have been detected and optimized with respect to the Er/Yb content and ratio, and proposed in particular for up- and down-conversion of solar spectrum for enhancement of the efficiency of solar cells. The rise and decay kinetics for the population of the excited levels of Er3+ and Yb3+ have been studied and fit. Based on these experimental data, the mechanisms for the energy transfers have been suggested with emphasis on the optimized Er/Yb content and ratio for enhancement of the efficiency of the Er3+↔Yb3+ energy transfers.

Abstract: We studied the morphology of ramps in REBa2CU3O7 (REBCO) epitaxial films on SrTiO3 substrates, fabricated by RF magnetron sputter deposition and pulsed laser deposition (PLD), by scanning probe microscopy (SPM) and high resolution electron microscopy (HREM). The ramps were fabricated by Ar ion beam etching using masks of standard photoresist and TIN. AFM-studies on ramps in sputter deposited films show a strong dependence, i.e. formation of facets and ridges, on the angle of incidence of the ion beam with respect to the substrate surface as well as the rotation angle with respect to the crystal axes of the substrate. Ramps in pulsed laser deposited films did not show this dependence, Furthermore, we studied the effect of an anneal step prior to the deposition of barrier layers (i.e. PrBa2CU3O7, SrTiO3, CeO2) on the ramp. First results show a recrystallization of the ramp surface, resulting in terraces and a non-homogeneous growth of the barrier material on top of it. The thickness variations, for thin layers of barrier material, con even become much larger than expected from the amount of deposited material and are dependent on the deposition and anneal conditions. HREM studies show a well defined interface between barrier layer and electrodes. The angle of the ramp depends on the etch rate of the mask and REBCO, and on the angle of incidence of the ion beam. TiN has a much lower etch rate compared to photoresist, resulting in an angle of the ramp comparable to the angle of incidence, resulting in a low etching rate on the ramp. These results will lead to improved electrical characteristics of ramp-type junctions.

Abstract: We present the post-modification of a gallium based Metal Organic Framework, COMOC-4, with a Mo-complex. The resulting Mo@COMOC-4 was characterized by means of N2 sorption, XRPD, DRIFT, TGA, XRF, XPS and TEM analysis. The results demonstrate that even at high Mo-complex loadings on the framework, no aggregation or any Mo or Mo oxide species are formed. Moreover, the Mo@COMOC-4 was evaluated as a catalyst in the epoxidation of cyclohexene, cyclooctene and cyclododecene employing TBHP in decane as oxidant. The post-modified COMOC-4 exhibits a very high selectivity toward the epoxide (up to 100%). Regenerability and stability tests have been carried out demonstrating that the catalyst can be recycled without leaching of Mo or loss of crystallinity.

Abstract: Au particles were prepared by evaporation in ultra high vacuum at high temperature, on the surfaces of TiO2 micro-spheres with the anatase structure. The morphology and the structural deformation in Au deposits were studied by high resolution transmission electron microscopy and image simulations by the multislice technique. The particles were polyhedral, limited by (100) and (111) faces. Patches with a hexagonal lattice were found around the particles, which was interpreted as thin Au islands on the surface. In these islands the Au lattice was deformed and perfectly accommodated to the (110) surface of TiO2. (C) 2001 Elsevier Science B.V. All rights reserved.

Abstract: In TEM, a typical goal consists of making a small electron probe in the sample plane in order to obtain high spatial resolution in scanning transmission electron microscopy. In order to do so, the phase of the electron wave is corrected to resemble a spherical wave compensating for aberrations in the magnetic lenses. In this contribution, we discuss the advantage of changing the phase of an electron wave in a specific way in order to obtain fundamentally different electron probes opening up new applications in the (S)TEM. We focus on electron vortex states as a specific family of waves with an azimuthal phase signature and discuss their properties, production and applications. The concepts presented here are rather general and also different classes of probes can be obtained in a similar fashion, showing that electron probes can be tuned to optimize a specific measurement or interaction.

Abstract: The giant cationic palladium clusters, approximate formula Pd561L60(OAc)180 (L = Dipy, Phen), were characterized by electron diffraction and high resolution microscopy to contain an FCC metal core, most of the larger Pd particles (8 nm) exhibiting multiple twinning, evidence for a distorted icosahedral structure.

Abstract: Oxygen deficient perovskites Sr0.75Y0.25Co1-xMnxO3-y, x=0.5 and 0.75, were prepared by using the citrate route at 1373-1573 K for 48 h. The cubic Pm-3m perovskite structure for x=0.5 was confirmed by electron diffraction study and refined using neutron powder diffraction (NPD) data. For x=0.75, the superstructure corresponding to a=root 2 x a(per), b=2 x a(per), c=root 2 x a(per) (a(0)b(-)b(-) tilt system, space group Imma) was revealed by electron diffraction. The solid solution Sr0.75-xCaxY0.25Co0.25Mn0.75O3-y, 0.1 <= x <= 0.6 and compound Ca0.75Y0.25Mn0.85Co0.15O2.92 were prepared in air at 1573 K for 48 h. The crystal structure of Ca0.75Y0.25Mn0.85Co0.15O2.92 was refined using NPD data (S.G. Pnma, a=5.36595(4), b=7.5091(6), c=5.2992(4) angstrom, R-p=0.057, R-wp=0.056, chi(2)=4.26). High-temperature thermal expansion properties of the prepared compounds were studied in air using both dilatometry and high-temperature X-ray powder diffraction data (HTXRPD). They expanding non-linearly at 298-1073 K due to the loss of oxygen at high temperatures. Calculated average thermal expansion coefficients (TECs) for Sr0.75Y0.25Co1-xMnxO3-y, x=0.5, 0.75 and Ca0.75Y0.25Mn0.85Co0.15O2.92(1) are 15.5, 15.1, and 13.8 ppm K-1, respectively. Anisotropy of the thermal expansion along different unit cell axes was observed for Sr0.15Ca0.6Y0.25Co0.25Mn0.75O3-y, and Ca0.75Y0.25Mn0.85Co0.15O2.92. Conductivity of Sr0.75Y0.25Co1-xMnxO3-y, x=0.5 and 0.75 increases with the temperature reaching 110 S/cm for x=0.5 and 44 S/cm for x=0.75 at 1173 K. Samples of Sr0.75-xCaxY0.25Co0.25Mn0.75O3-y, 0.1 <= y <= 0.6 were found to be n-type conductors at room temperature with the similar temperature dependence of the conductivity and demonstrated the increase of the sigma value from similar to 1 to similar to 50 S/cm as the temperature increases from 300 to 1173 K. Their conductivity is described in terms of the small polaron charge transport with the activation energy (E-p) increasing from 340 to 430 meV with an increase of the calcium content from x=0 to x=0.6. (C) 2012 Elsevier Inc. All rights reserved.