Synthesis of Core-Shell Nanocrystals with InAs Cores

1 Synthesis of Core-Shell Nanocrystals with InAs Cores Preparation of the InAs core-shell nanocrystals is carried out in a two-step process. In the first step, the InAs cores are prepared using the injection method with TOP as solvent. This allowed hundreds of milligrams of nanocrystals per synthesis to be obtained (as detailed above), with a size-selective precipitation being used to improve the size distribution of cores to a 10%. In the second step, the shells of the various materials were grown on the prepared cores. This two-step approach followed methods developed for the synthesis of group II-VI core-shell nanocrystals. 

Details of the synthesis of core-shell nanocrystals are available elsewhere [6, 7]. Briefly, TOP-capped InAs cores (5-20mg) were dissolved in 3-6 g of TOP (or a mixture with TOPO) in a three-necked flask. Under an Ar flow on a Schlenk line, the nanocrystal solution was heated to 260 °C, and the shell precursor solution introduced into the hot solution by drop-wise addition. The growth of core-shells was monitored using UV-visible spectroscopy of aliquots taken from the reaction flask. Following growth of the desired shell thickness the reaction mixture was cooled to room temperature, after which the core-shell nanocrystals passivated by TOP were obtained by precipitation, using a mixture of methanol and toluene. 

In contrast to the group III-V semiconductor shells, growth of the II-VI semiconductor shells (CdSe, ZnSe, and ZnS) was observed at low temperatures above 150 °C. For the CdSe shells, by limiting the nucleation such that a controlled shell 

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