Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

Figure 3 Transmission electron micrograph of 8.5 nm diameter CdSe nanocrystalsdemonstrating the high degree of size monodispersity achieved by the ‘‘sizefocusing’’synthesis method. (From Ref. 14, reprinted with permission.)(by removing the heat source), and sizes are limited to those relatively close tothe initial nucleation size. Because nucleation size can be manipulated bychanging precursor concentration or reaction injection temperature, narrowsize dispersions of controlled average particle size can be obtained by thismethod of simply stopping the reaction shortly following nucleation, duringthe rapid-growth stage.Because of the ease with which high-quality samples can be prepared,the II–VI compound CdSe has compromised the ‘‘model’’ NQD system andbeen the subject of much basic research into the electronic and optical propertiesof NQDs. CdSe NQDs can be reliably prepared from pyrolysis of avariety of cadmium precursors, including alkyl cadmium compounds (e.g.,dimethylcadmium [15]) and various cadmium salts (cadmium oxide, cadmiumacetate, and cadmium carbonate [16]), combined with a selenium precursorprepared simply from Se powder dissolved in trioctylphosphine (TOP)or tributylphosphine (TBP). Initially, the surfactant–solvent combination,technical-grade trioctylphosphine oxide (tech-TOPO) and TOP, was used,Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.