537 research outputs found
N,N′-Bis(phenylsulfonyl)maleamide. Corrigendum
No full textThe chemical name of the title compound in the paper by Gowda, Foro, Suchetan & Fuess [Acta Cryst. (2010), E66, o187] is corrected
Contributions of Crystallography to Materials Science
No full textThe properties o fmaterials used in various domains of science and engineering are directly correlated to the microstructure. Crystallography is devoted to the investigaton of microstructure of substances and materials by a variety of diffraction and spectroscopic methods. Several examples related to research in the department of materials science at the Technical University of Darmstadt are presented. The structure and dynamics of aromatic host molecules in catalytically active zeolites are investigated by X-ray and neutron diffraction and NMR-spectroscopy combined with inelastic neutron scattering. Surfaces and interfaces of semiconductors and thin superconducting films are studied by grazing incidence techniques. By examination of the reflectogram details on thickness, composition, surface roughness and a possible modification of these values are obtained. Transmission electron microscopy provides complementary information on the structure of interfaces, especially through the support of simulated images by a multi-slice method. Work is presented on CoSi2-filmson Si and wafers of GaAs with LaB6 films. Modification of the seewafers by ion mixing techniques is attempted. Furthermore, surface hardening of steel by ion implantation (carbon and nitrogen) is away of improving tribological properties. Grazing incidence provides results on the formation of different carbides as a function of depth. Superconducting films of Bi2Sr2CaCu20s on SrTi03 showed an improvement by a factor of 10 in critical current density by creating holes (Xe,Au, U'-irradiation) as pinning centres. The examination by TEM revealed an amorphization of the channel s with dear boundaries between the channel and nonirradiated material
Matériaux nanostructurés à base d'étain
No full textDes matériaux hybrides de classe II ont été préparés à partir de précurseurs bis(tripropynylstannylés). Deux familles de précurseurs sol-gel incluant des espaceurs hydrocarbonés et thiophénique ont été obtenues et conduisent à des matériaux hybrides auto-organisés où les plans d’oxyde sont séparés par les espaceurs organiques. Ainsi l’espaceur rigide a donné lieu à une structure pseudo-lamellaire montrant une bande d’émission monomère avec un assez faible décalage vers le rouge par rapport à l'émission des précurseurs en solution. En revanche, alors que les xérogels thiényle plus désordonnés conduisent à une large émission caractéristique de la formation d’excimères ou de dimères. Par ailleurs, des films minces contenant les espaceurs alkylène et arylalkylène ont été préparés et ont montré une morphologie "pseudoparticulaire" poreuse et un ordre à courte distance contenant des réseaux SnOx. De façon inattendue, ces films minces hybrides détectent le dihydrogène dès une température de 50 °C dans la gamme 200-10000 ppm. A partir de ces films hybrides minces, le dioxyde d'étain cristallin (SnO2) a été préparé par un post-traitement thermique. Comme prévu, ces films SnO2 cassitérite détectent le dihydrogène et, dans une moindre mesure le monoxyde de carbone avec une température optimale de fonctionnement comprise entre 300 et 350 °C.Class II hybrid materials were prepared from ditin hexaalkynides. Two families of precursors, including either hydrocarbon or oligothiophene-based spacers, were obtained and led by the sol-gel process to self-assembled organotin-based hybrid materials made of planes of oxide separated by organic bridges. Thus, the rigid thienyl spacer gave rise to a “pseudo-lamellar” structure that showed a monomer emission band with a rather small red-shift compared with to the emission of the precursor in solution. However more disordered thienyl xerogels led to broad emission features assigned to excimer or dimer formation. Moreover, thin films containing alkylene- and arylalkylene bridged have been prepared and showed a “pseudoparticulate” porous morphology and a short-range hierarchical order in the organic-inorganic SnOx pseudoparticles. Unexpectedly these hybrid thin films detect hydrogen gas at a temperature as low as 50 °C at the 200-10000 ppm level. From these hybrid thin films, crystalline tin dioxide (SnO2) were prepared by a thermal post-treatment. As expected, cassiterite SnO2 films detected H2 and to a less extent CO with a best operating temperature comprised between 300 and 350 °C
Neutron scattering, neutron diffraction: hydrogen location, cation distribution, magnetic structures
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