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A tunable library of substituted thiourea precursors to metal sulfide nanocrystals

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Science  12 Jun 2015:
Vol. 348, Issue 6240, pp. 1226-1230
DOI: 10.1126/science.aaa2951

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Quality manufacture beats quality control

For semiconductor nanocrystals, tight control over particle size is needed to obtain particles with uniform properties. However, post-synthesis purification methods can be difficult and costly. Hendricks et al. present a family of substituted thioureas as a class of chalcogen precursors (see the Perspective by Hens). The rate of reactivity is connected to the specific chemistry of the precursor, making it possible to synthesize metal chalcogenide nanocrystals, such as PbS, with a specific size, narrow size distribution, and full conversion of the reactants.

Science, this issue p. 1226; see also p. 1211

Abstract

Controlling the size of colloidal nanocrystals is essential to optimizing their performance in optoelectronic devices, catalysis, and imaging applications. Traditional synthetic methods control size by terminating the growth, an approach that limits the reaction yield and causes batch-to-batch variability. Herein we report a library of thioureas whose substitution pattern tunes their conversion reactivity over more than five orders of magnitude and demonstrate that faster thiourea conversion kinetics increases the extent of crystal nucleation. Tunable kinetics thereby allows the nanocrystal concentration to be adjusted and a desired crystal size to be prepared at full conversion. Controlled precursor reactivity and quantitative conversion improve the batch-to-batch consistency of the final nanocrystal size at industrially relevant reaction scales.

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