How Different Characterization Techniques Elucidate the Nature of the Gold Species in a Polycrystalline Au/TiO2 Catalyst

TiO₂‐supported gold species were prepared via the deposition‐precipitation route, with conservation of the initial speciation by freeze‐drying. The structural and electronic properties of the Au species were investigated by X‐ray absorption spectroscopy, electron microscopy, and IR spectroscopy of adsorbed CO in four states. Exclusively Au^III was deposited on the TiO₂ surface in patches ranging from isolated Au ions to three‐dimensional clusters. This paper illustrates in detail the unique contributions of all characterization techniques to this structural model.     

Distribution of GABA and glycine receptors on bipolar and ganglion cells in the mammalian retina

The amino acids GABA and glycine mediate synaptic transmission via specific neurotransmitter receptors. Molecular cloning studies have shown that there is a great diversity of GABA and glycine receptors. In the present article, the distribution of GABA and glycine receptors on identified bipolar and ganglion cell types in the mammalian retina is reviewed. Immunofluorescence obtained with antibodies against GABA and glycine receptors is punctate. Electron microscopy shows that the puncta represent a cluster of receptors at synaptic sites. Bipolar cell types were identified with immunohistochemical markers. Double immunofluorescence with subunit-specific antibodies was used to analyze the distribution of receptor clusters on bipolar axon terminals. The OFF cone bipolar cells seem to be dominated by glycinergic input, whereas the ON cone bipolar and rod bipolar cells are dominated by GABAergic input. Ganglion cells were intracellularly injected with Neurobiotin, visualized with Streptavidin coupled to FITC, and subsequently stained with subunit specific antibodies. The distribution and density of receptor clusters containing the alpha1 subunit of the GABA(A) receptor and the alpha1 subunit of the glycine receptor, respectively, were analyzed on midget and parasol cells in the marmoset (a New World monkey). Both GABA(A) and glycine receptors are distributed uniformly along the dendrites of ON and OFF types of parasol and midget ganglion cells, indicating that functional differences between these subtypes of ganglion cells are not determined by GABA or glycinergic input.     

Direct observation of inelastic deformation and mechanochemical activation of indented quartz single crystals

In a basic study of the mechanism of mechanochemical activation of fine powdery materials, a large single crystal of quartz was stressed by loading with a diamond indenter. The stressed crystal was subsequently immersed in 1 N KOH solution at 60 °C for various periods. The microstructures of the indented region before and after immersion were observed under a scanning electron microscope, in order to examine the direct correlation between the manner and the extent of deformation and the degree of activation. Inelastic deformation was recognized by indenting under a load as low as 1 kp. As the force is related to the area of indentation, the corresponding local pressure amounts to about 10 GPa. At higher loads, very fine fragments were produced and deformed highly inelastically. This part of the material dissolved preferentially because of the enhanced reactivity. It was thus verified qualitatively that the enduring effect of mechanochemical activation is a consequence of the inelastic deformation.     

Application of ultraviolet photoelectron spectroscopy (UPS) in the surface characterisation of polycrystalline oxide catalysts. I. Methodics and analytical potential

Polycrystalline oxide surfaces have been investigated by a combination of photoemission and ion-scattering techniques (UPS, XPS, ISS) to assess the analytical potential of UPS for the surface characterisation of real polycrystalline oxide catalysts. UP spectra can be obtained from a number of binary and ternary oxides when the measurement is performed at appropriate temperatures in order to ensure sample conductivity sufficient to avoid surface charging. Where applicable, UPS provides enhanced surface sensitivity (as compared to XPS) and chemical sensitivity permitting the identification of surface structures and adsorbates. The benefit of enhanced surface sensitivity has been demonstrated by the detection of V⁴⁺ species in the outmost surface layer(s) of V₂O₅. The use of the chemical sensitivity for the identification of chemical compounds on a fingerprint basis has been shown by a study of bismuth molybdate surfaces. The chemical sensitivity with respect to adsorbates has been demonstrated by the detection of N-containing species formed in the interaction of V₂O₅ with NH₃.     

Robotic deposition of 3d nanocomposite and ceramic fiber architectures via UV curable colloidal inks

A novel approach for producing predetermined, complex 3d ceramic architectures by robotic deposition where UV radiation is used for solidification is presented. Homogeneous, highly loaded, solvent free colloidal inks with controlled viscoelastic properties are achieved by proper selection of monomers and surfactants. Room temperature deposition of complex 3d fiber networks having filaments in the 100 μm range is demonstrated for Al₂O₃ and hydroxyapatite model particles for structural and biomedical applications. Solidification of the structures by UV radiation allows additional shaping of the structures by post-printing processes such as cutting, folding and bonding. 2d and 3d architectures with high aspect ratios retain their shape and transform to macroscopic ceramics after thermal debinding and sintering procedures. Sintered alumina fiber networks functionalized with a 3-5 μm layer of TiO₂ nanoparticles exhibit photocatalytic activity for the decomposition of formaldehyde as a similar weight of loose powder, indicating possible applications in catalytic reactors prototypes.     

In Situ Tensile Measurements of Single Fibers by Scanning Electron Microscopy

A newly developed tensile module allows tensile experiments of single fibers to be carried out under visual observation in the scanning electron microscope. This allows correlation of measured data with observed changes in the microstructure, such as surface irregularities and crack formation. With point heating, the thermal behavior of the fibers may be studied up to 2500°C. The results are presented with tensile elongation recordings and micrograph sequences of the structural changes. Carbon fibers with and without an aluminum coating were selected as testing specimens.