Silver anisotropic

When a nanoporous Ti02 film consisting of Ti02 nanoparticles is used instead of the single crystal, the extinction band of silver nanoparticles deposited by UV-irradiation is much broader. This is probably because the nanopores in the Ti02 film mold the silver nanoparticles into various anisotropic shapes [9], although direct observation of the particles in the nanopores is difficult. 

In the closely related compound AgCuS, the sulfur atoms form a slightly distorted hexagonal close-packed array. The Cu+ ions are located in positions within this framework to form layers, while the Ag+ ions lie between the sulfur-copper layers. These Ag+ ions show a progressively greater anisotropic thermal motion as the temperature rises, until, above 93°C, they are essentially completely mobile, leading to extremely high silver ion conductivity. 

Silver nitrate in ammoniacal solution may be completely reduced to silver by aqueous arsenious oxide. The reduction is hindered by the presence of ammonium sulphate, owing to the decrease in concentration of the hydroxyl ions 5 neutral salts such as sodium sulphate or sodium nitrate have no effect. Similarly, auric chloride may be reduced to gold.6 At 20° C. an aqueous solution of vitreous arsenious oxide reacts 4 to 5 times as rapidly as an aqueous solution of the octahedral form 7 the greater rate of dissolution in water of the former variety has been mentioned (p. 137), but from supersaturated solutions of the two forms there is no appreciable difference in the rates of deposition. The explanation of the inferior reducing power of the crystalline variety may be that there exist anisotropic molecules which only slowly lose their anisotropic properties. An ammoniacal solution of arsenious oxide heated with cupric sulphate in a sealed tube at 100° C. causes reduction... 

The electrodeposition of thallium on Ag(l 10) is similar to that which takes place on the (111) face of silver [122]. The voltammogram shows well-defined structure in the formation of the first monolayer, and further deposition occurs before formation of the bulk deposit. Fig. 5.16c and d display the results for the isotropic and anisotropic response respectively. The magnitude and phase of o 2 were modeled by a constant contribution from the adatoms throughout the adsorption process (Eq. (5.4)). Values of x /Xin = 0-94 and a phase shift of 131° were obtained. As with Ag(lll), an enhancement in the anisotropic response was observed beyond 1 monolayer and was attributed to a similar resonance effect. 

Anisotropic bimetallic nanoparticles can also be synthesized by radiolysis. Indeed, /-irradiation of an aqueous solution containing silver and platinum metal ions and a polymer (PVA), at dose rates lower than 0.5 kGy.h , led to the synthesis of wire-like Ag-Pt structures with lengths up to 3.5 pm and diameters between 3 and 20 nm.ii7... 

Many experiments have been carried out to investigate the use of silva nanoparticies as a sacrificial template for the deposition of an outer shell of material. The silver is oxidized away during the deposition of the outer shell in a process known as galvanic replacement. This is a process whereby a metal is deposited as a result of the reduction of relevant ions by another metal with a lower reduction potential. Silver is a choice template material for this as it easily forms a whole range of anisotropic shapes. 

Aslan, K., Lakowicz, J.R., and Geddes, C.D. (2005). Metal-enhanced fluorescence using anisotropic silver nanostructures critical progress to date. Anal. Bioanal. Chem. 382 926-933. 

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