Silver clusters size effects

Next we study the effects of the cluster size on DOS. When the cluster size is increased, the interactions between neighboring atoms with long distances are taken into account, then the electronic state approaches that of btilk. Figure 12 compares DOS of the clusters Nig, Nij3, Nijj and Ni j, as well as bulk crystaP by a band structure calculation. Usually the band structure of the bulk crystal can be rather well reproduced if we take several ten atoms in the model cluster for transition elements, though the small cluster model provides somewhat narrower d band. In the case of the element with a d band which is almost completely occupied, for example the case of silver, the size effect is not very large, but a small cluster already well represents the band structure of bulk as shown in Fig. 13. 

Fig. 1 The effect of size on metals. Whereas bulk metal and metal nanoparticles have a continuous band of energy levels, the limited number of atoms in metal clusters results in discrete energy levels, allowing interaction with light by electronic transitions between energy levels. Metal clusters bridge the gap between single atoms and nanoparticles. Even though in the figure the energy levels are denoted as singlets, we must remark that the spin state of the silver clusters is not yet firmly established...

Tsunoyama H, Sakurai H, Tsukuda T (2006) Size effect on the catalysis of gold clusters dispersed in water for aerobic oxidation of alcohol. Chem Phys Lett 429 528 Pradhan N, Pal A, Pal T (2002) Silver nanoparticle catalyzed reduction of aromatic nitro compounds. Colloids Surf A 196 247... 

Hence, experimental rate constant measurements in combination with theoretical simulations show a pronounced size and structure selective activity of anionic silver clusters toward molecular oxygen due to cooperative effects. In particular, for Ag clusters with odd n, a weakly bound first O2 promotes the adsorption of a second O2 molecule which is then (for n = 3, 5) differently bound with the O2 bond elongated to 1.32 A and thus potentially activated for further oxidation reactions such as CO combustion, which have indeed been observed for larger cluster sizes [361]. 

Lerme, J., Palpant, B., Prevel, B., Pellarin, M., Treilleux, M., Vialle, J.L., Perez. A.. Broyer. M. Quenching of the size effects in free and matrix-embedded silver clusters. Phys. Rev. Lett. 80, 5105-5108 (1998)... 

The interaction of a chlorine atom (hole) with a silver cluster depends markedly upon cluster size. This effect can be inferred from the general decrease in IP as cluster size increases (Figure 3) as manifested in the Cl difference spectra (Figure 6). The Cl difference spectra show a shift of 0.5 eV towards Ep (Table II) with increasing cluster size. Of course only the direction of shift is important in correlations with the IP change since the partially covalent bonding with Cl complicates the situation. 

Size Dependence of E (Ag, -Ag ). The quantum-size effect on metal clusters redox properties in solution is the most important feature for cluster chemistry in solution. Most of data have been obtained on silver clusters suitable as an experimental model (J-4, 22). 

In spite of great interest in preparation and studying of silver clusters Ag , their structures are not clearly determined yet. Thus, only structures of clusters with n=3,4,5 are fairly well established. The most effective method of investigations of clusters structures is a comparison of quantum chemical predictions for different stable geometries with experimental data. The central problem in reliable identification of clusters structures by this method is an increase of the amount of structures characterized by closely allied values of energetic characteristics as the size of the cluster grows. As a consequence, structural assigmnent even for relatively simple clusters is a very difficult problem [1]. 

Lu J, Cheng L, Lau KC et al (2014) Effect of the size-selective silver clusters on lithium peroxide morphology in lithium-oxygen batteries. Nat Common 5 4895. doi 10.1038/ ncomms5895... 

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