Structure nanoclusters

Leung K, Pokrant S and Whaley K B 1998 Exciton fine structure in CdSe nanoclusters Phys. Rev. B 57 12 291... 

The surface consists of terraces of a height of 330 30 pm. Within error limits, this is the value that would be expected for Ge(lll) bilayers. Furthermore, we were able to observe that the electrodeposition gave rise to a less ordered surface structure with nanoclusters, transforming over a timescale of about 1 hour into a layered structure. With GeBr4 a transformation of clusters into such a layered surface was only partly seen with GeGl4 this transformation could not be observed. 

Over the last few years, we have made a number of novel discoveries using reactive salt fluxes in the crystal growth experiment of mixed-metal oxides. The most important outcome that these salt-inclusion solids have demonstrated is the propensity for structure- directing effects of the employed salt. These hybrid solids have revealed fascinating solid-state structures ranging from nanoclusters to three-dimensional open frameworks of current interest. Solids featuring mag-... 

Dynamic light-scattering experiments or the analysis of some physicochemical properties have shown that finite amounts of formamide, A-methylformamide, AA-dimethyl-formamide, ethylene glycol, glycerol, acetonitrile, methanol, and 1,2 propanediol can be entrapped within the micellar core of AOT-reversed micelles [33-36], The encapsulation of formamide and A-methylformamide nanoclusters in AOT-reversed micelles involves a significant breakage of the H-bond network characterizing their structure in the pure state. Moreover, from solvation dynamics measurements it was deduced that the intramicellar formamide is nearly completely immobilized [34,35],... 

J. M. (1998) Lowest Energy Structures of Gold Nanoclusters. Physical Review Letters, 81, 1600-1603. 

Sharma, P., Singh, H Sharma, S. and Singh, H. (2007) Binding of Gold Nanoclusters with Size-Expanded DNA Bases A Computational Study of Structural and Electronic Properties. Journal of Chemical Theory and Computation, 3, 2301-2311. 

Hakkinen, H., Abbet, S., Sanchez, A., Heiz, U. and Landman, U. (2003) Structural, Electronic, and Impurity-DopingEffects in Nanoscale Chemistry Supported Cold Nanoclusters. Angewandte Chemie International Edition, 42, 1297-1300. 

Finke has reported remarkable catalytic lifetimes for the polyoxoanion- and tetrabutylammonium-stabi-lized transition metal nanoclusters [288-292]. For example in the catalytic hydrogenation of cyclohexene, a common test for structure insensitive reactions, the lr(0) nanocluster [296] showed up to 18,000 total turnovers with turnover frequencies of 3200 h [293]. As many as 190,000 turnovers were reported in the case of the Rh(0) analogue reported recently. Obviously, the polyoxoanion component prevents the precious metal nanoparticles from aggregating so that the active metals exhibit a high surface area [297]. 

Zero-Dimensional Structures SET on Single Chemically Tailored Nanoclusters... 

Alivisatos and coworkers reported on the realization of an electrode structure scaled down to the level of a single Au nanocluster [24]. They combined optical lithography and angle evaporation techniques (see previous discussion of SET-device fabrication) to define a narrow gap of a few nanometers between two Au leads on a Si substrate. The Au leads were functionalized with hexane-1,6-dithiol, which binds linearly to the Au surface. 5.8 nm Au nanoclusters were immobilized from solution between the leads via the free dithiol end, which faces the solution. Slight current steps in the I U) characteristic at 77K were reflected by the resulting device (see Figure 8). By curve fitting to classical Coulomb blockade models, the resistances are 32 MQ and 2 G 2, respectively, and the junction... 

Figure 26. Constant current mode STM image of isolated (A), self-organized in close-packed hexagonal network (C) and in fee structure (E) of silver nanoclusters deposited on Au(l 11) substrate (scan size (A) 17.1 x 17.1 nm, f/t=—IV, /t=ltiA, (C) 136 X 136 nm, f/t = — 2.5 V, /t = 0.8 tiA, (E) 143 x 143 nm, = —2.2 V, /, = 0.72 nA). I U) curves and their derivatives in the inserts of isolated (B), self-organized in close-packed hexagonal network (D) and in fee structure (F) of silver nanoclusters deposited on Au(l 11) substrate. (Reprinted with permission from Ref. [58], 2000, Wiley-VCH.)...

It can be readily anticipated that the new instrumentation, having extended the point resolution of the microscope up to its information limit [117], will provide even better high resolution images of nanoclusters, and also that it will not supersede, but emphasize, the role of EH, as the relevant structural information encoded in the phase (which is still completely lost in the recording process) can be retrieved corrected by all coherent aberrations. 

Platinum Nanoclusters Size and Surface Structure Sensitivity of Catalytic Reactions... 

Metal Nanoclusters in Catalysis Effects of Nanoparticle Size, Shape, and Structure... 

Supported metal catalysts, M°/S, are typically two-components materials built up with a nanostructured metal component, in which the metal centre is in the zero oxidation state (M°), and with an inorganic support (S), quite various in its chemical and structural features [1], M° is the component typically deputed to the electronic activation of the reagents involved in the catalyzed reactions. S is typically a microstructured component mainly deputed to the physical support and to the dispersion of M° nanoclusters. 

The catalytic chemistry of M° depends on the elementary properties of M and on the structure and size of the M° nanoclusters ( quantum dots ) [2]. S may play a role as a reactivity enhancer of M°/S as a whole (co-catalytic role) and/or as a promoter of its catalytic chemoselectivity (promotional role) [3,4]. 

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