Silver nanocrystals

Flarfenist S A and Wang Z L 1999 Fligh-temperature stability of passivated silver nanocrystal superlattices J. Phys. Chem. B 103 4342... 

FIG. 4 5-nm silver nanocrystals self-organized in very large crystalline structure. 

When the silver nanocrystals are organized in a 2D superlattice, the plasmon peak is shifted toward an energy lower than that obtained in solution (Fig. 6). The covered support is washed with hexane, and the nanoparticles are dispersed again in the solvent. The absorption spectrum of the latter solution is similar to that used to cover the support (free particles in hexane). This clearly indicates that the shift in the absorption spectrum of nanosized silver particles is due to their self-organization on the support. The bandwidth of the plasmon peak (1.3 eV) obtained after deposition is larger than that in solution (0.9 eV). This can be attributed to a change in the dielectric constant of the composite medium. Similar behavior is observed for various nanocrystal sizes (from 3 to 8 nm). 

Boleininger, J., Kurz, A., Reuss, V. and Sonnichsen, C. (2006) Microfluidic continuous flow synthesis of rod-shaped gold and silver nanocrystals. Physical Chemistry Chemical Physics, 8, 3824-3827. 

Nina P, Galina A, Claudio R, de la Fernando Vega, Aharon Gedanken (2009) Sonochemical deposition of magnetite on silver nanocrystals. Ultrason Sonochem 16(1) 132—135... 

Shah, P.S., Husain, S., Johnston, K.P. and Korgel, B.A. (2002) Role of steric stabilization on the arrested growth of silver nanocrystals in supercritical carbon dioxide. Journal of Physical Chemistry B, 106 (47), 12178-12185. 

Roque J, Molera J, Sciau P, Pantos E, Vendrell-Saz M (2006) Copper and silver nanocrystals in lustre lead glazes development and optical properties. J European Ceramic Society 26 3813-3824. 

Motte L. and Pileni M. P., Self-assemblies of silver nanocrystals influence of length of thiol-alkyl chains used as coating agent. Applied Surface Science 164 (2000) pp. 60-67. 

Figure 7 Characterization of silver nanoparticles produced by AG4 clone, (a) TEM micrograph of silver nanocrystal morphologies obtained from AG4 clone, (b c) TEM micrographs of silver nanoparticles with AG4 peptides. Inset in (b) is electron diffraction pattern from [111] beam direction for fee crystal, (d) Edge of truncated silver crystal, (e) EDX spectrum indicative for the presence of silver, Cu, and carbon are due to grid. (Reproduced by permission of Nature Publishing Group (www.nature.com))...

Tao, A., Sinsermsuksakul, P. and Yang, P. (2006). Polyhedral silver nanocrystals with distinct scattering signatures. Angew.-Chem., Int. Ed 45 4597-4601. 

Bosnick KA, Jiang J, Brus LE (2002) Fluctuations and local symmetry in single-molecule Rhodamine 6G Raman scattering on silver nanocrystal aggregates. J Phys Chem B 106 8096... 

Cobley CM, Rycenga M, Zhou F, Li ZY, Xia Y (2009) Etching and growth an intertwined pathway to silver nanocrystals with exotic shapes. Angew Chem Inter Ed 48 4824... 

Harfenist SA, Wang ZL, Alvarez MM, Vezmar I, Whetten RL (1997) Three-dimertsional superlattice packing of faceted silver nanocrystals. Nanophase and nanocomposite materials II. Mater Res Soc SympProc 457 137-142... 

Hamanaka, Y., Nakamura, A., Omi, S., Del Fatti, N., Vallee, F., Flytzanis, C. Ultrafast response of nonlinear refractive index of silver nanocrystals embedded in glass. Appl. Phys. Lett. 75, 1712-1714 (1999)... 

Supercritical fluids may be utilized for the synthesis of metal nanoparticles. Perfluorodecanethiol-stabilized silver nanocrystals were synthesized in supercritical CO2 through arrested precipitation, by reducing silver acetylacet-onate with hydrogen in the presence of fluorinated thiol (Figure 8). The CO2 density used during synthesis controls the particle size and polydispersity. At... 

Figure 8 Transmission electron micrograph of silver nanocrystals synthesized in supercritical fluid CO2 with perfluoroalkanethiol ligands illustrating the 111 lattice plane. (From Ref. 25.)...

Figure 1. Schematic of perfluorodecanethiol capped silver nanocrystal...

Short alkanes such as decane and dodecane are completely miscible in sc-CO2 at moderate pressures and temperatures. Based on the earlier simulations, it would seem that nanocrystals capped with dodecanethiol should disperse in sc-CO2 at moderate conditions however, this is not the case. Gold and silver nanocrystals capped with dodecanethiol ligands were exposed to SC-CO2 at pressures as high as 483 bar and temperatures up to 80 C without any visible dispersibility. This indicates that ligands with better CO2 compatibility need to be developed to allow for effective dispersibility. The dodecanethiol capped nanocrystals were dispersible in sc-ethane, as the solvent-ligand interactions were much more compatible. 

Figure 2. Absorbance spectra for silver nanocrystals in sc-ethane - a) 35 C and various pressures b) 414 bar and various temperatures, (Reproduced from reference 13. Copyright 2002 American Chemical Society.)...

Finally, the precipitation and redispersion of the silver nanocrystals was found to be nearly reversible. After precipitating the largest nanocrystals of a polydisperse dispersion by lowering the system pressure from 414 bar to 276 bar, and then repressurizing to 414 bar, 90% of the silver nanocrystals redispersed. Reversible nanocrystal flocculation has potential value in fine-tuning size-dependent separations with minor variations in pressure. Reversible solvation conditions are difficult to achieve using a conventional anti-solvent approach. 

Figure 4. UV-visible absorbance spectra of perfluorodecanethiol capped silver nanocrystals dispersed in SC-CO2 at 80 C.

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