Polarization-dependent soft-x-ray absorption of a highly oriented ZnO microrod-array.

Polarization-dependent x-ray absorption measurements were performed on a crystalline ZnO three-dimensional array consisting of highly oriented microrods as well as on particulate thin film consisting of monodisperse spherical nanoparticles. Strong anisotropic effects have been observed for the highly oriented ZnO rods, unlike for the isotropic spherical ones. Full-potential calculations of orbital-resolved x-ray absorption of a ZnO wurtzite periodic crystal, including the Zn 3d as part of the valence states, shows a very good agreement with the experimental findings. Comprehensive fundamental knowledge of the electronic structure of ZnO is obtained by probing and demonstrating the orbital symmetry of oxygen and its contribution to the conduction band of this important II-VI semiconductor.

Aqueous chemical growth of alpha-Fe2O3-alpha-Cr2O3 nanocomposite thin films.

We are reporting here on the inexpensive fabrication and optical properties of an iron(III) oxide-chromium(III) oxide nanocomposite thin film of corundum crystal structure. Its novel and unique-designed architecture consists of uniformed, well-defined and oriented nanorods of Hematite (alpha-Fe2O3) of 50 nm in diameter and 500 nm in length and homogeneously distributed nonaggregated monodisperse spherical nanoparticles of Eskolaite (alpha-Cr2O3) of 250 nm in diameter. This alpha-Fe2O3-alpha-Cr2O3 nanocomposite thin film is obtained by growing, directly onto transparent polycrystalline conducting substrate, an oriented layer of hematite nanorods and growing subsequently, the eskolaite layer. The synthesis is carried out by a template-free, low-temperature, multilayer thin film coating process using aqueous solution of metal salts as precursors. Almost 100% of the light is absorbed by the composite film between 300 and 525 nm and 40% at 800 nm which yields great expectations as photoanode materials for photovoltaic cells and photocatalytic devices.

Size Tailoring of Magnetite Particles Formed by Aqueous Precipitation: An Example of Thermodynamic Stability of Nanometric Oxide Particles.

The particle mean size of magnetite precipitated in aqueous solution can be adjusted and stabilized against ripening over a large range at the nanometric scale (1.5-12.5 nm). Such a tailoring of particles is obtained by controlling the pH and the ionic strength imposed by a noncomplexing salt in the precipitation medium. The higher the pH and the ionic strength are, the smaller the particle size is. Above a critical pH value, which depends on the ionic strength and the temperature, the secondary particle growth by Ostwald ripening does not take place anymore. The stabilization of nanoparticles seems to result from thermodynamics rather than kinetics. Copyright 1998 Academic Press.