Halides chemically modified surfaces

Redox Chemistry of the Group 5 Clusters Ligand Substitution Electronic and Molecular Structure Niobium Iodide Clusters NbJJ"-Materials Chemistry Derived from Soluble Metal Halide Clusters A. Higher Nuclearity Clusters Supported Cluster Materials Charge-Transfer Salt Complexes Extended Solids Chemically Modified Surfaces... 

Inside" processes—such as modified chemical vapor deposition (MCVD) and plasma chemical vapor deposition (PCVD)—deposit doped silica on the interior surface of a fused silica tube. In MCVD, the oxidation of the halide reactants is initiated by a flame that heats the outside of the tube (Figure 4.8). In PCVD, the reaction is initiated by a microwave plasma. More than a hundred different layers with different refractive indexes (a function of glass composition) may be deposited by either process before the tube is collapsed to form a glass rod. 

Superadditivity has been observed in both chemical and physical development [52] thus the presence of silver halide is not a necessary condition for its occurrence but is likely to modify its detailed course. This would appear to rule out the charge-barrier theory in its original form, although charge effects might also occur at silver as well as at silver halide surfaces. 

Aleskovsky, Kolstov, Volkova, and co-workers investigated the chemical modification of silica surfaces by inorganic compounds (274-281). The materials obtained are useful in heterogeneous catalysis, electronics, and so forth. The method for molecular lamination was developed (276-278) by interacting volatile and readily hydrolyzing halides of transitional metals with the surface of hydroxylated silica. This method makes it possible to modify the silica surface with mono- and polymolecular layers of V, Cr, Ti, Fe, Al, B, and so forth. 

In addition to diazonium salts, there are many other species that are able, once electrochemicaUy activated, to modify the surface with aromatics, unsaturated and saturated groups. These surface modifications can be achieved by (i) oxidation (amines, hydrazines, alcohols, carboxylates, carbamates, carbanions, Grignard reagents) (ii) reduction, some being closely related to diazonium salts (iodoniums, sulfonium) and other different species (vinylics, alkyl halide) (iii) spontaneously, chemically or pho-tochemically (alcenes, azides, peroxides). Note that electrochemical oxidation methods can be applied only to the materials that can withstand quite positive potentials such as carbon or Pt. This section will describe these modifications [357]. 

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