133 research outputs found
Electron microscopy study of CeOx–Pd/α-Al2O3 catalysts for methane dry reforming
We have investigated the interaction between Pd and Ce in a 0.47 wt % CeOx–Pd 1 wt %/ -Al2O3 catalyst that is used in the reforming reaction of CH4 with CO2. The freshly reduced catalyst was characterized by various electron microscopy techniques, such as elemental mapping, Z-contrast imaging, and electron energy-loss spectroscopy to understand the role of Ce on a microscopic scale. The high spatial resolution elemental mapping indicates that CeOx is located in close proximity of the palladium nanoparticles. High-resolution lattice images and energy-loss spectra obtained in the vicinity of the Pd particles show an anisotropic distribution of CeOx crystallites limited to the interface region between Pd and the substrate but not covering the surface of the Pd nanoparticles. Energy-loss near edge fine structure of Pd M edges reveals that the Pd nanoparticles are not oxidized.Fil: Moreno, M. S.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Wang, Feiya. National Institute for Nanotechnology; CanadáFil: Malac, M.. National Institute for Nanotechnology; CanadáFil: Kasama, T.. University of Cambridge; Reino UnidoFil: Gigola, Carlos Eugenio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Costilla, Ignacio Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Sánchez, M. D.. Universidad Nacional del Sur. Departamento de Física; Argentin
Electron Energy Loss Spectroscopy Study on the Dielectric Response of Single H2Ti3O7 Nanotube
Blending of nanoscale and microscale in uniform large-area sculptured thin-film architectures
The combination of large thickness ( m), large--area uniformity (75
mm diameter), high growth rate (up to 0.4 m/min) in assemblies of
complex--shaped nanowires on lithographically defined patterns has been
achieved for the first time. The nanoscale and the microscale have thus been
blended together in sculptured thin films with transverse architectures.
SiO () nanowires were grown by electron--beam evaporation onto
silicon substrates both with and without photoresist lines (1--D arrays) and
checkerboard (2--D arrays) patterns. Atomic self--shadowing due to
oblique--angle deposition enables the nanowires to grow continuously, to change
direction abruptly, and to maintain constant cross--sectional diameter. The
selective growth of nanowire assemblies on the top surfaces of both 1--D and
2--D arrays can be understood and predicted using simple geometrical shadowing
equations.Comment: 17 pages, 9 figure
Microstructure and Structural Defects in MgB2 Superconductor
We report a detailed study of the microstructure and defects in sintered
polycrystalline MgB2. Both TEM and x-ray data reveal that MgO is the major
second-phase in our bulk samples. Although MgB2 and MgO have different crystal
symmetries, being P6/mmm and Fm-3m, respectively, their stacking sequence of Mg
and B (or O) and lattice spacings in certain crystallographic orientations are
very similar. The size of MgO varies from 10~500nm, and its mismatch with the
MgB2 matrix can be a source for dislocations. Dislocations in MgB2 often have a
Burgers vector of . 1/3 and 1/3 partial dislocations and their
associated stacking faults were also observed. Since both dislocations and
stacking faults are located in the (001) basal plane, flux pinning anisotropy
is expected. Diffuse scattering analysis suggests that the correlation length
along the c-axis for defect-free basal planes is about 50nm. (001) twist
grain-boundaries, formed by rotations along the c-axis, are major grain
boundaries in MgB2 as a result of the out-of-plane weak bonding between Mg and
B atoms. An excess of Mg was observed in some grain boundaries. High-resolution
nano-probe EELS reveals that there is a difference in near edge structure of
the boron K-edge acquired from grain boundaries and grain interiors. The change
at the edge threshold may be suggestive of variation of the hole concentration
that would significantly alter boundary superconductivity.Comment: 20 pages and 12 figure
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