Solid State Phenomena Vols. 99-100

Abstract: The paper briefly reviews some fundamental and applicative characteristics of the laser pyrolysis technique. Recent developments of this method for the synthesis of iron-based nanostructures are emphasized. By varying the precursor gas mixture, iron/carbon nanocomposites (core-shell structures) and gamma iron oxide nanopowders were obtained and characterized. Novel structural features of the synthesized titanium-doped nano iron oxides are described.

Abstract: Applying the Karlsruhe Microwave Plasma Process, alumina and zirconia particles with particle sizes in the range from 2 to 5 nm were synthesized. Additionally, the influence of small amounts of iron(III)-oxide, chromia, and magnesia on the crystallization and phase transitions in alumina powders was investigated. It is shown that these dopants may influence the crystallization behavior significantly. Especially, the addition of 1 mol% iron(III)-oxide reduced the temperature of the formation of a-alumina from 1200 °C to 300 °C.

Abstract: Star-shaped and rod-like PbS crystals have been successfully prepared by a novel thioglycolic acid (TGA) assisted hydrothermal method. X-ray diffraction (XRD) reveals that the PbS crystals are of the cubic rock-salt structure and well formed. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observations show that the morphology of PbS nanocrystals is easily controlled according to sulphur source, lead source, and pH value. Furthermore, the paper gives a preliminary presntation of the mechanism and the critical role of the TGA-assisted hydrothermal synthesis of PbS nanorods

Abstract: A TGA assisted hydrothermal process was employed to prepare chalcogenide nanorods. The different morphology of CdS nanomaterials prepared with and without the TGA assisted hydrothermal process indicates that TGA plays a critical role in controlling the nucleation and growth of CdS nanomaterials. The paper makes a preliminary presentation of the mechanisms of preparation of chalcogenide nanostructures with and without the use of the TGA assisted hydrothermal synthesis. FeS nanorods and nanoparticles have been prepared by the TGA assisted and without the TGA assisted hydrothermal process, respectively, which confirmed the proposed mechanism. X-ray diffraction (XRD) shows that the nanorods are of orthorhombic structure, and selected area electron diffraction (SAED) pattern showed that the FeS nanorods were single crystalse. Further investigation for the synthesis of other chalcogenides will be undertaken in order to confirm the proposed mechanism.

Abstract: Thermal surface purification in an inert gas flow and densification processes of SiC and diamond nanocrystalline powders with specific surface in the range of 60 – 300 m2/g and average grain sizes from 5 to 15 nm in diameter were examined. Termogravimetric Analysis (TGA) linked with mass spectrometry of outgassing products show that surface impurities desorb at up to 450°C. Further heating above 450°C leads to oxidation of the powder surface. Small Angle X-Ray Scattering (SAXS) and gas porosimetry (ASAP) was applied to investigate densification of the nanocrystalline powders. Compaction under 1GPa or higher pressure was found necessary for obtaining the ceramic matrix with porosity in the nanometer range.

Abstract: Silver sodalite crystals with hydroxyl guest anion and silver loading higher than 7.9 per unit cell were investigated. EPR spectra of sodalite, recorded just afer g-irradiation at 77K, shows a 9-line, near isotropic signal with giso=1.987 and hyperfine splitting of 8.3 mT. The signal decays completely above 200K. We assign the multiplet to silver octamer Ag8 n+ cluster and tentatively postulate that the cluster charge is +7.

Abstract: Ab initio slab simulations were performed for copper adhesion to a perfect MgO(001) surface using the DFT-LCGTF method as implemented in CRYSTAL98 computer code. In order to clarify the nature of interfacial bonding, we considered a slab model of the Cu/MgO(001) interface with regular 1/4 monolayer (ML), 1/2 ML, 1 ML and 2 ML substrate coverages and verified the results of our calculations. In particular, the dependences of the adhesion energy per Cu atom, projections of multipole moments as well as total and projected densities of states (DOS) on the substrate coverage by a metal are analyzed. Computer simulation indicated that physical adsorption makes the dominant contribution to bonding on the regular Cu/MgO(001) interface.

Abstract: The equations of motion are derived for a magnetic planar system with dipolar interactions taken into account. Magnetostatic waves propagating perpendicularly to the sample surface and dipolar field static and dynamic components are calculated for the case when saturating field is applied perpendicularly to the sample surface. The corresponding frequency spectra and mode profiles are computed numerically with emphasis laid on size effects. It is established that two lowest-frequency modes are surface-localized modes. These modes preserve their surface-localized character with growing sample dimensions.

Abstract: The perspectives of synthesis of highly-organized nanostructured solids and materials with various levels of microscopic organization are discussed. The synthesis and the magnetic properties of mixed Fe-Eu-oxygen groups on silica surface are given as an example. It is shown that spin arrangement ions and the appearance of two-dimensional magnetic ordering are defined to the structural induced effects of sublayer as well as the first layer composition.

Abstract: Experiments to directly bond AlN with Cu were conducted for different pre-treatments of the bonded components. AlN substrates were implanted either with oxygen, or titanium or iron ions at low (15 keV) or high (70 keV) energy, or thermally oxidized. Some Ti-implanted samples were also thermally oxidized. The copper component was annealed and thermally oxidized. The best results, with respect to the bond shear strength, were obtained for low-energy implantation of oxygen and titanium.