Silver clusters, annealing

Room temperature deposition of silver on Pd(lOO) produces a rather sharp Ag/Pd interface [62]. The interaction with a palladium surface induces a shift of Ag 3d core levels to lower binding energies (up to 0.7 eV) while the Pd 3d level BE, is virtually unchanged. In the same time silver deposition alters the palladium valence band already at small silver coverage. Annealing of the Ag/Pd system at 520 K induces inter-diffusion of Ag and Pd atoms at all silver coverage. In the case when silver multilayer was deposited on the palladium surface, the layered silver transforms into a clustered structure slightly enriched with Pd atoms. A hybridization of the localized Pd 4d level and the silver sp-band produces virtual bound state at 2eV below the Fermi level. 

Ag-NaA zeolites Silver clusters Silver clusters, formed in X-ray irradiated samples at 77 K and annealed at 280 K, were characterized by electron spin resonance spectroscopy 556... 

The use of y-irradiation and controlled thermal annealing to produce silver clusters in zeolites and related materials was reviewed by Michalik [114]. Unusual stability was attributed to Ag + clusters formed in this way in dehydrated zeolite rho, which were found to persist for months at room temperature and could be observed up to 100°C. In the zeoHte A analogue, AgH-SAPO-42 (LTA), dehydrated at 300 °C in flowing oxygen, clusters such as AgJ and Agf" were detected in very low yield, but, in the presence of methanol, Agl" species were... 

Further annealing induces additional Ag overlayer enrichment with Pd atoms, causing a substantial intensity increase of the Pd resonant state, while the intensity at the Fermi level remained very small. This is a clear indication of the localized character of the Pd 4d state. The annealing of the Ag multilayer produces a surface alloy with a composition very close to Ago.sPdo.s which has a DOS at the Fermi level substantially smaller than the pure palladium. The annealing at higher temperature produces a Pd(l 10) surface with very small but very persistent amount of silver, which is in the form of three-dimensional clusters, located most probably below the first Pd(l 1 0) layer. 

In this part of the chapter we discuss (a) the controlled thermolysis of thiolate solutions in polystyrene matrix at temperatures above the polymer glass transition temperature and (b) the reaction mechanism in the case of silver-polystyrene nanocomposite systems. However, the same reaction mechanism is probably involved in the thermolysis of other mercaptide-polystyrene systems. This technique has proven to be an excellent new preparative scheme for the generation of both metal and sulfide clusters in polymers. In particular, high-molecular-weight n-alkanethiolates have shown to be the most effective compound class since the low volatility of thermolysis by-products avoids film foaming during the annealing process. 

Figure 5.7. TEM micrographs of polystyrene-embedded metal clusters (a) Palladium (Pd(SCi2H25)2-polystyrene was annealed at 170°C for 5min), (b) gold (AuSC,2H25-polystyrene was annealed at 180°C for 5min), and (c) silver (AgSQjHjy-polystyrene was annealed at 150°C for 1 min).

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