Silver electronic properties

Bonacic-Koutecky, V., Burda, J., Mitric, R., Ge, M., Zampella, G. and Fantucci, P. (2002) Density functional study of structural and electronic properties of bimetallic silver - gold clusters Comparison with pure gold and silver clusters./oumol of Chemical Physics, 117, 3120-3131. 

In Section 2 the general features of the electronic structure of supported metal nanoparticles are reviewed from both experimental and theoretical point of view. Section 3 gives an introduction to sample preparation. In Section 4 the size-dependent electronic properties of silver nanoparticles are presented as an illustrative example, while in Section 5 correlation is sought between the electronic structure and the catalytic properties of gold nanoparticles, with special emphasis on substrate-related issues. 

The effect of microwave irradiation on the catalytic properties of a silver catalyst (Ag/Al203) in ethane epoxidation was studied by Klimov et al. [91]. It was found that on catalyst previously reduced with hydrogen the rates of both epoxidation and carbon dioxide formation increased considerably on exposure to a microwave field. This effect gradually decreased or even disappeared as the catalyst attained the steady state. It was suggested that this was very likely because of modification of electronic properties of the catalyst exposed to microwave irradiation. 

Most of the other metal-related deep levels in Si are also passivated by reaction with hydrogen (Pearton, 1985). Silver, for example, gives rise in general to a donor level at Ee + 0.54 eV and an acceptor level at Ec - 0.54 e V (Chen and Milnes, 1980 Milnes, 1973). These levels are very similar to those shown by Au, Co and Rh and raise the question of whether Au might actually be introduced into all of the reported samples or a contaminant, or whether as discussed by several authors there is a similar core to these impurity centers giving rise to similar electronic properties (Mesli et al., 1987 Lang et al., 1980). This problem has not been adequately decided at this time. It has been... 

The first deals with small islands of silver on a ruthenium substrate. One may look at this sample as a, perhaps somewhat far-fetched, model of a supported catalyst or a bimetallic surface. As metal layers are almost never in perfect registry with the substrate, they possess a certain amount of strain. Goodman and coworkers [46] used these strained metal overlayers as model systems for bimetallic catalysts. Here we look first at the electronic properties of the Ag/Ru(001) system as studied by UPS. 

Kreibig, U., 1974. Electronic properties of small silver particles the optical constants and their temperature dependence, J. Phys. F., 4, 999-1014. 

All of the studies discussed above for silver have been done with an incident beam of 1064 nm. These studies have proven that the anisotropy in the nonlinear polarizability from the silver surface is not purely free-electron-like at these wavelengths, that the anisotropy can be correlated with surface symmetry, and that the SH response measured in situ is nearly identical to that measured in UHV. The issue of the sensitivity of the rotational anisotropy to surface electronic properties has been the topic of very recent work which has been conducted by variation of the incident wavelengths to where optical resonances in the bulk or surface electronic structure can be accessed. 

The Principle of Hard and Soft Acids and Bases states that hard acids form more stable complexes with hard bases and soft bases form more stable complexes with soft acids. In orbital terms hard molecules have a large gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), and soft molecules have a small HOMO-LUMO gap. In recent years it has been possible to correlate the hardness with the electronic properties of the atoms involved. Thus, if the enthalpy of ionisation (I) and the electron affinity (A) are known the so-called absolute hardness (t ) and absolute electronegativity (%) can be found from r = (I - A) / 2 and % = (I + A) / 2. For example, the first and second ionisation enthalpies of sodium are 5.14 and 47.29 eV. Thus for Na+, I = + 47.29 and A = + 5.14, so r = (47.29 - 5.14) / 2 = 21.1. Similarly for silver the first and second ionisation enthalpies are 7.58 and 21.49eV, so for Ag+ we have, n = (21.49 - 7.58) 12 = 6.9. 

The electronic properties of small silver clusters chemisorbed on AgBr have been calculated by Baetzold (66) using MO theory. This problem deals with catalysis since, as Hamilton and Urbach (67) have described, the silver centers are catalysts for the chemical reduction of AgBr grains. By using various experimental techniques, they indicate that a minimum size cluster of 4 Ag atoms is required for the catalysis. This suggests that some properties of 4 bonded silver atoms are different from atomic and perhaps like bulk properties, which could account for the catalysis. 

Electronic Properties. When the silver aggregate grows, its properties become more like those of bulk silver. These calculations for Ag atoms added at lattice positions show that a single atom on the crystal has a charge of +0.52, which is comparable to the average AgBr lattice cation charge of +0.55 calculated by... 

As mentioned above, electronic properties of CNTs depend on the chirality and presence of defects in the scrolled graphene layer. Metallic nanotubes can have an electric current density more than 1,000 times greater than metals such as silver and copper. All nanotubes are expected to be very good thermal conductors along the tube, but good insulators laterally to the tube axis.8... 

Rather dramatic alterations in the electronic properties and relaxation dynamics of supported silver atoms and clusters have been traced to extremely subtle differences in ground and excited state guest-host interaction potentials. For Ag° and Ag2+ in faujasite zeolites, pronounced changes in their optical... 

Conducting (conjugated) polymers have a unique set of properties The electronic properties of metals and semiconductors and the processing advantages and mechanical properties of polymers. It is the and that makes conducting polymers special materials. There are, after all, many excellent metals for example, copper, nickel, silver and gold, to name but a few. Similarly, there are many excellent semiconductors. Indeed, the sophisticated modem electronics industry uses silicon as the semiconductor of choice. It would be difficult to improve on the quality of copper as a metal or silicon as a semiconductor. 

Sato and Seo have studied the electronic properties of the subsurface oxide film by monitoring the continuous exo-electron emission which occurs on silver catalysts during an epoxidation reaction. They interpreted this effect as a thermo-electron emission from a non-stoicheiometric semi-conducting oxide film present on silver, the work function of which is lowered by the adsorption of ethylene. The heat of formation of the film was calculated to be 45 kJ mol L No exo-electron emission was observed on non-epoxidation catalysts, including copper. 

One way in which the adsorption of a chlorine atom could affect more than one adsorption site is if the chlorine is incorporated into the subsurface oxide layer. No direct evidence of chloride accumulation in the catalyst subsurface has been published. However, there is at 373 K an apparent competition between chlorine and oxygen for adsorption sites which, we have argued above, correspond to the formation of the first monolayer of the oxide film. In view of this it would be surprising if chloride accumulation in the subsurface did not occur under practical epoxidation conditions. The net result would be to modify the electronic properties of this semi-conducting layer and hence the adsorptive properties of the surface. The chloride catalysed reorganization of surface silver atoms is perhaps indirect evidence of such an affect. ... 

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