Monodisperse colloidal nanocrystals

KINETICS OF COLLOIDAL CHEMICAL SYNTHESIS OF MONODISPERSE SPHERICAL NANOCRYSTALS... 

When two monodisperse colloids of CoPts nanocrystals (4.5 nm and 2.6 nm diameter) were mixed together, followed by a slow evaporation of the solvent, an ABs-type superlattice analogous to the structure of intermetallic compound CaCus [42] was obtained (Figure 4.18) [26]. A similar stmcture was observed for binary mixtures of latex spheres of two different sizes [43,44]. In the first plane of this lattice (Figure 4.18), each 4.5 nm CoPt3 nanocrystal is surrounded with a hexagon formed by 2.6 nm nanocrystals. The second plane consists only of hexagons of small particles, while the third plane repeats the first. 

The most successful NQD preparations with respect to nanocrystal quality and monodispersity entail pyrolysis of metal-organic precursors in hot coordinating solvents (120 360 °C). Understood in terms of La Mer and Dinegar s studies of colloidal particle nucleation and growth, these preparative routes involve a temporally discrete nucleation event followed by relatively rapid growth from solution-phase monomers and finally slower growth by Ostwald... 

CdTe quantum dots, resulting in polydisperse nanocrystals. Polydispersity was quantitatively assessed from the polydispersity index (PDI) in gel filtration chromatograms. When the MCR values are above 2.0, the excess polymer leads to better monodispersity and colloidal stability, but a reduced fluorescence quantum yield. Between these two limits is the optimal capping ratio (OCR) of approximately 1.5, yielding small, monodisperse nanocrystals (PDI < 1.5) with bright fluorescence ( 50% quantum yield) and exceptional photostability. 

Whetten and coworkers separated the crude thiol-protected gold particles by fractional crystallization until monodisperse fractions were obtained. Electron microscopy of these nanocrystals showed that the major components of the thiol-capped colloid have the gold core as a truncated octahedron containing, in accord with the geometrical predictions, 140, 225, 314 and 459 gold atoms487. 

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