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

particles [1,3,4]. Consequently, a large number of nucleation centers areinitially formed, and the coordinating ligands in the hot solvent prevent orlimit particle growth via Ostwald ripening (the growth of larger particles atthe expense of smaller particles to minimize the higher surface free energyassociated with smaller particles). Futher improvement of the resulting sizedistribution of the QD particles can be achieved through selective precipitation[3,4], whereby slow addition of a nonsolvent to the colloidal solution ofparticles causes precipitation of the larger-sized particles (the solubility ofmolecules with the same type of chemical structure decreases with increasingsize). This process can be repeated several times to narrow the size distributionof II–VI colloidal QDs to several percent of the mean diameter [3,4].The synthesis of colloidal III–V QDs is more difficult than for II–VIQDs. The reason is that III–V semiconductor compounds are more covalentand high temperatures are required for their synthesis. To use the colloidalchemical method for the synthesis of QDs, it is important that the stabilizerand solvent do not decompose during the reaction period in order to ensuregood solubility of QDs after synthesis and to avoid extensive formation oftrap states on the surface. The preparation method is a compromise betweenthese two requirements. One difference compared to the synthesis describedearlier for II–VI materials is that several days of heating at a reactiontemperature are required to form crystalline III–V QDS, whereas II–VIQDs form immediately upon injection of the reactants into the hot coordinatingsolution. The synthesis must also be conducted in rigorously air-freeand water-free atmospheres, and it generally requires higher reaction temperatures.The best results to date for III–V QDs have been obtained for InP QDs[5–10]. Figure 1 shows transmission electron microscopic (TEM) images ofnanocrystalline InP QDs.1. Colloidal InP Quantum DotsIn this synthesis, an indium salt [e.g., In(C 2 O 4 )C1, InF 3 , or InCl 3 ] is reactedwith trimethylsilylphosphine P[Si(CH 3 ) 3 ] 3 in a solution of trioctylphosphineoxide (TOPO) and trioctylphosphine (TOP) to form a soluble InP organometallicprecursor species that contains In and P in a 1:1 ratio [5,8]. The precursorsolution is then heated at 250–290jC for 1–6 d, depending on desiredQD properties. Use of TOPO/TOP as a colloidal stabilizer was first reportedby Murray et al. [4], who showed the remarkable ability of TOPO/TOP tostabilize semiconductor CdSe QDs at high temperature. Different particlesizes of InP QDs can be obtained by changing the temperature at which thesolution is heated. The duration of heating only slightly affects the particlesize, but does improve the QD crystallinity. The precursor has a highCopyright 2004 by Marcel Dekker, Inc. All Rights Reserved.