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

synthesis temperatures of z400jC are required to promote these processesleading to crystalline growth [54,55]. Such conditions can preclude theformation of kinetic, or higher-energy, materials and can limit the selectionof accessible materials to those formed under thermodynamic control—thelowest-energy structures [56,57]. In contrast, biological and organic–chemicalsynthetic strategies, often relying on catalyzed growth to surmount or lowerenergybarriers, permit access to both lowest-energy and higher-energy products[56], as well as access to a greater variety of structural isomers comparedto traditional, solid-state synthetic methods. The relatively low-temperature,surfactant-supported, solution-based reactions employed in the synthesis ofNQDs provide for the possibility of forming kinetic phases (i.e., those phasesthat form the fastest under conditions that prevent equilibrium to the lowestenergystructures). Formation of the CdSe zinc-blende phase, as opposed tothe wurzite structure, is likely a kinetic product of low-temperature growth. Ingeneral, however, examples are relatively limited. More examples are to befound in the preparation of nonmolecular solid thin films: electrodepositiononto single-crystal templating substrates [58], chemical vapor depositionusing single-source precursors having both the target elements and the targetstructure built in [59], and reaction of nano-thin-film, multilayer reactants togrow metastable, superlattice compounds [60–62]. One clear example fromthe solution phase is that of the formation of the metastable, previouslyunknown, rhombohedral InS (R-InS) phase [63]. The organometallic precursort-Bu 3 In was reacted with H 2 S(g) at f200jC in the presence of a proticreagent, benzenethiol. This reagent provided the apparent dual function ofcatalyzing efficient alkyl elimination and supplying some degree of surfactantstabilization. Although the starting materials were soluble, the final productwas not. Nevertheless, characterization by TEM and powder X-ray diffraction(XRD) revealed that the solid-phase product was a new layered InSphase, structurally distinct from the thermodynamic network structure—orthorhombic h-InS. Further, the new phase was 10.6% less dense comparedto h-InS and was, therefore, predicted to be a low-temperature kineticstructure. To confirm the relative kinetic-thermodynamic relationshipbetween R-InS and h-InS, the new phase was placed back into an organicsolvent (reflux temperature f200jC) in the presence of a molten indium metalflux. The metal flux (molten nanodroplets) provided a convenient recrystallizationmedium, effecting equilibration of the layered and network structuresallowing conversion to the more stable, thermodynamic network h-InS. Thesame phase transition can occur by simple solid-state annealing; however,significantly higher temperatures (>400jC) are required. That the fluxmediatedprocess involves true, direct conversion of one phase to the other(rather than dissolution into the flux followed by nucleation and crystallization)was demonstrated by subjecting a sample powder containing significantCopyright 2004 by Marcel Dekker, Inc. All Rights Reserved.