Cobalt thin films were produced by metal-organic CVD from C 5 H 5 Co(CO) 2 , at various temperatures and for various deposition times. The films have been grown onto glass substrates with no buffer. The crystalline structure, morphology, and composition of the films were analyzed by X-ray diffractometry (XRD), field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and Auger electron spectroscopy (AES). Routine XRD patterns were collected in symmetric geometry for phase identification and the sin 2 w diffraction technique was employed to calculate the average in-plane stress. Structural studies indicate that the films tend to grow in island mode, as predicted by theory, and have a structure between that of face-centered cubic (fcc) and hexagonal close-packed (hcp) cobalt. There is significant in-plane tensile stress at the interface with the substrate, which relaxes to a compressive stress an order of magnitude lower at the surface. The films have a relatively low impurity content, as determined by AES, except near the surface.

Magnetic transitions in single-crystal ␣-Fe 2 O 3 ͑hematite͒ nanowires, grown by thermal oxidation of iron powder, have been studied in the range of 5 -1023 K with a superconducting quantum interference device below room temperature and with a vibrating sample magnetometer at higher temperatures. The broad temperature range covered enables us to compare magnetic transitions in the nanowires with the transitions reported for bulk hematite. Morin temperatures ͑T M ͒ of the nanowires and of hematite bulk reference powder were found to be 123 and 263 K, respectively. Also the Néel temperature ͑T N ͒ of the nanowires, 852 K, was lower than the bulk T N value. Measurements of the magnetization as a function of temperature show an enhanced signal in the nanowires, which suggests a decrease in the antiferromagnetic coupling. A coercive field observed below T M in the hysteresis loops of the nanowires is tentatively explained by the presence of a magnetic phase.

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α -Fe 2 O 3 (hematite) nanostructures with various morphologies have been grown by thermal oxidation of compacted iron powder at temperatures between 700 and 900 °C. Different thermal treatments have been found to induce the growth of single-crystalline nanowires, nanobelts, nanoplates and featherlike structures, free and caped nanopillars, and pyramidal microcrystals or cactuslike microstructures. The experimental conditions leading to the different morphologies have been systematically investigated, as well as the possible growth mechanisms. The obtained nanostructures have been characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy, x-ray diffraction, and cathodoluminescence (CL) spectroscopy in the SEM. The formation of the nanostructures induces changes in the intensity and spectral distribution of the CL emission, as compared with the bulk material. Ligand to metal charge transfer transitions as well as Fe3+ ligand field transitions are thought to be involved in the observed luminescence. The evolution of the panchromatic CL intensity in the visible range as a function of temperature shows some anomalies that may be induced by magnetic ordering effects.