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

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

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Figure 31 Dark-field optical micrograph of faceted CdSe colloidal crystals. Thecrystals were prepared <strong>by</strong> slow self-assembly of 2.0-nm-diameter NQDs thatnucleated homogeneously from solution. A mixed nonpolar/polar solvent systemsimilar to that depicted in Fig. 30b was used in combination with careful regulationof solution temperature and pressure to provide the necessary conditions forcontrolled destabilization of the NQD starting solution. The colloidal crystals arestacked and range in size from 5 to 50 Am. (From Ref. 90, reprinted with permission.)alcohol (assuming the NQDs are surface terminated with long-chain alkyls)over time (Fig. 30b) [8]. The process can be controlled <strong>by</strong> applying heat and/orvacuum to the system. Free-standing and surface-bound colloidal [facecentered-cubic(fcc)] crystals exhibiting long-range order over hundreds ofmicrons have been prepared in this way. In addition, the individual NQDs cancrystallographically orient as demonstrated <strong>by</strong> small-angle and wide-anglex-ray scattering for a CdSe NQD thin film in which the wurtzite c axis of thenanocrystals are aligned in the plane of the substrate [8,90].<strong>Copyright</strong> <strong>2004</strong> <strong>by</strong> <strong>Marcel</strong> <strong>Dekker</strong>, <strong>Inc</strong>. <strong>All</strong> <strong>Rights</strong> <strong>Reserved</strong>.

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