Formation of CdTeS Prenucleation Clusters at Elevated Temperatures and Transformation to Magic-Size Clusters at Room Temperature.

The synthesis of colloidal semiconductor magic-size clusters (MSCs) of ternary II-VI metal chalcogenide (ME1E2) remains challenging. Using CdTeS as a model system, it is shown that CdTeS MSC-381 (displaying sharp optical absorption peaking at 381 nm) develops at room temperature from prenucleation-stage samples of reactions of Cd(OAc)2/OLA (cadmium acetate in oleylamine), TeTOP (tri-n-octylphosphine telluride), and S (sulfur). It is proposed that the three precursors experience physical co-self-assembly followed by the formation of Te-Cd-S covalent bonds inside each assembly. Chemical self-assembly results in the occurrence of prenucleation clusters (PNCs), which are the precursor compound (PC-381) of MSC-381. High feed concentrations and Cd-to-E molar ratios promote the co-self-assembly, which is participated more by the precursor molecule of Te than by that of S. With compelling evidence for the formation of ternary PNCs at elevated temperatures and for the PC-to-MSC transformation at room temperature, these findings suggest that chemical self-assembly occurs generally in reactions.