ZnCl2 Mediated Synthesis of InAs Nanocrystals with Aminoarsine

The most developed approaches for the synthesis of InAs nanocrystals (NCs) rely on pyrophoric, toxic and not readily available tris-trimethylsilyl or tris-trimethylgermil arsine (TMS-As) precursors. Alternative less toxic and commercially-available chemicals, such as dimethylamino-arsine (amino-As), emerged as alternative As precursors. Nevertheless, InAs NCs made with such compounds need to be further optimized, in terms of size distribution and optical properties, in order to meet the standard reached with TMS-As. To this aim, in this work we investigated the role of ZnCl₂ used as an additive in the synthesis of InAs NCs with amino-As and alane N,N-dimethylethylamine. We discovered that ZnCl₂ helps not only to improve the size distribution of InAs NCs, but also to passivate their surface acting as a Z-type ligand. The presence of ZnCl₂ on the surface of the NCs and the excess of Zn precursor used in the synthesis enable the subsequent in-situ growth of a ZnSe shell, which is realized by simply adding the Se precursor to the crude reaction mixture. The resulting InAs@ZnSe core@shell NCs exhibit photoluminescence emission at ~860 nm with quantum yields as high as 42%, which is a record for such heterostructures, given the relatively high mismatch (6%) between InAs and ZnSe. Such bright emission was ascribed to the formation of an In-rich intermediate layer inbetween the core and the shell, as indicated by X-ray photoelectron spectroscopy and elemental analyses, which helps to release the strain between these two materials.