Colloidal nanocrystals made of III-V materials are of considerable technological interested based on the impressive performance of their bulk counterparts. For the most part only indium pnictide nanocrystals (InP, InAs, InSb) have been prepared via solution phase routes with high quality optical properties and narrow size distributions. Colloidal synthesis of Ga- and Al-pnictide phases is difficult due to the extreme oxophilicity of typical Ga and Al precursors and the high temperatures typically needed to achieve crystalline phases. Recently our group has demonstrated a route for converting InP and InAs nanocrystals to their respective In1-xGaxP and In1-xGaxAs ternary alloys. This has been achieved using GaI3 as a gallium source and a variety of eutectic salts as the solvent including CsBr/KBr/LiBr, LiI/KI, and GaI3/KI eutectic melts. Generalizing these approaches to prepare In1-xGaxSb from InSb were unsuccessful and instead resulted in decomposition of the materials to its constituent elements. We found that incorporating Ga+ ions in the molten salt solvents prevents decomposition of the InSb nanocrystals and enables the preparation of In1-xGaxSb with controlled composition. Further we found that molten salt solvents containing Ga+ ions were active for cation exchange of InP and InAs nanocrystals demonstrating its generality. We use this newfound stability to prepare In1-xGaxAs1-ySby nanocrystals via cation exchange from InAs1-ySby nanocrystals, representing a framework for preparing quaternary III-V alloys with independent control over the composition. This has important implications for heterostructure engineering of colloidal III-V nanocrystals since independent control over the composition of a quaternary alloy allows for independent tuning of the lattice parameter and band gap, for a given particle size. Finally, we elucidate the key reactive species present in the molten salts using in-situ Raman spectroscopy and discuss the mechanisms controlling stability of III-V nanocrystals in molten salts based on reduced gallium salts.

Synthesis of colloidal In1-xGaxSb nanocrystals via cation exchange enabled by controlling the redox environment in molten salt solvents

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