Au 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 20. I U) curves for Cg-Au (left) and Gal-Au (right) in H2O as a function of pH (adjusted with phosphate buffer). The numbers 1—4 in the Gal-Au data identify voltage plateaus. Cartoons of the experimental arrangements for measuring curves of individual nanoclusters in solution are shown at the top of each data column. The insulated STM tip, ligand-capped Au nanocluster and an octanethiol-coated planar Au substrate are shown. Length and shapes are not to scale. (Reprinted with permission from Ref. [35], 1998, American Chemical Society.)...

To study the nucleation and growth of Au nanoclusters in silica within the above theoretical frame, we implanted fused silica slides with 190keV-energy Au ions, at room temperature and current densities lower than 2 pA/cm, to reduce sample heating [49,50]. The implantation conditions were chosen to have, after annealing, a subsurface buried layer of Au nanoparticle precipitation of about... 

Figure 5. Transmission electron micrographs of Au nanoclusters deposited on the surfaces of the polycrystalline ellipsoidal hematite particles. The left photograph is a close-up view of the right one.

Table 4. Pd and Au nanoclusters size vs. determined nanoporosity in water.

Yagi I, Ishida T, et al. 2004. Electrocatal)tic reduction of oxygen to water at Au nanoclusters vacuum-evaporated on boron-doped diamond in acidic solution. Electrochem Commun 6 773-779. 

Synthesis of Au75from Au55 Phosphine-protected Au nanoclusters, Au55(PPh3) 2Cl6, were reacted with hexanethiol and other thiols leading to the formation of Au75... 

Fig. 4 (a) Excitation (dashed) and emission (solid) spectra of different Au nanoclusters. Excitation and emission maxima shift to longer wavelength with increasing nanocluster size, (b) Emission from the three shortest wavelength-emitting Au-nanocluster solutions (from left to right) under UV irradiation (366 nm) [1]... 

Fig. 5 Photostability of fluorescent Au nanoclusters (AuNC DHLA) compared with semiconductor quantum dots (polymer-coated QD 520 from Invitrogen) and organic fluorophores (fluorescein, rhodamine 6G) [12]...

The exceptional renewed interest in supported gold catalysts leads us to mention here a few recent examples of the formation of in situ gold carbonyl species from supported gold that can be related to the preparation of supported Au nanoclusters [53-55]. On the other hand, bimetallic carbonyl cluster salts of [Au4Fe4(CO)i,5] and [AuFe4(CO)i,5] have been used recently in the preparation of Au/Fe0,t/Ti02 catalysts for the total oxidation of dichlorobenzene and toluene [56]. 

Furthermore, it is reported that metal catalysts usually require a basic pH for sufficient activity for the aerobic oxidation of alcohols in water [85]. Thus, Biffis found that the productivity of the Au nanoclusters can be enhanced by running the reaction at basic pH (pH 9.9) in their system. However, further enhancement of the pH of the reaction solution was not possible, due to the precipitation of catalyst caused by the increased hydrophobicity of the microgel through deprotonation of the polymer-bound amino groups [84]. In our work, we tried to carry out the catalytic reaction... 

Figure 6.35. Hydrophobic-functionalized PAMAM (G4-Ci2) and poly(propyleneimine) (PPI) dendri-mers, which serve as templates for Au nanocluster growth. Reproduced with permission from Knecht, M. R. Garcia-Martinez, J. C. Crooks, R. M. Langmuir 2005, 21, 11981. Copyright 2005 American Chemical Society.

Zhang C, Yoon B, Landman U (2007) Predicted oxidation of CO catalyzed by Au nanoclusters on a thin defect-free MgO film supported on a Mo(lOO) surface. J Am Chem Soc 129 2228... 

Cotell, C.M., Schiestel, S., Carosella, C.A., Flom, S., Hubler, G.K., Knies, D.L. Ion-beam assisted deposition of Au nanocluster/Nb2O5 thin films with nonlinear optical properties. Nucl. Instr. and Meth. in Phys. Res. B 127/128, 557-561 (1997)... 

Valden, M. Goodman, D.W. Structure-activity correlations for Au nanoclusters supported on... 

Figure 5.3 Scheme for micronanopatterning of Au nanoclusters on solid surface. The micelles were deposited on the substrate surface by dipping it into the micelle solution (left). The chemical properties of the micelles cast on the substrate surface were modified by exposure to electron beam. Those unexposed areas were removed selectively. After plasma treatment, the gold-containing micelles remaining on the surface were converted to metallic Au nanoclusters. (From Glass et al.55 Reproduced with permission.)... 

Figure 1. Assembly of the Au nanoclusters at the air/aqueous solution interface.

Figure 3. SEM image of the Au nanocluster superlattices. The samples were grown from a suspension 22°C.

Figure 4. TEM image of the Au nanocluster superlattice (a) overall shape, and (b) magnification of the part outlined in image (a). The superlattice was grown from a suspension at 22 C. The sample was scooped with a specimen grid covered by a perforated carbon film.

Figure 7. SEM image of the Au nanocluster aggregates grown at an air/suspension interface at 35 C. The HCl concentration in the suspension was adjusted to 0.3 M and the sample was scooped with a silicon wafer. 

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