Multiple Roles of Magic-Sized Clusters in Quantum Dot Synthesis

Abstract

Magic-sized clusters (MSCs) are often observed as intermediates during the growth of semiconductor quantum dots (QDs) as transiently thermodynamically stable, with diameters typically ranging 1-2 nm. Exploiting MSCs as a new class of precursors for QD syntheses is of great importance. Roles of MSCs in the nucleation and growth of QDs and interactions between MSCs and conventional molecular precursors have attracted intensive attention. During QD synthesis, an MSC can convert to another MSC or an amorphous cluster. It can also be fragmentized into smaller clusters and molecular species such as metal-ligand complexes, which in turn can be used as a molecular precursor for nucleation or growth of QDs. Two different MSCs, F393-InP:Zn MSC and F360-InP:Zn MSC, were used as a QD synthesis precursor. They acted as a precursor cargo supplying the indium-octadecylphosphonate (In-ODPA) complex, which was subsequently consumed for QD growth. The F393-InP:Zn MSC has higher thermal stability than the F360-InP:Zn MSC. As a result, the F393-InP:Zn MSC released In-ODPA complexes at a higher temperature than the F360-InP:Zn MSC, which could hinder ripening and/or continuous nucleation and yielded narrowly size-distributed QDs. The F360-InP:Zn MSC provided In-ODPA complexes at an earlier stage of QD synthesis, and recreation of the MSC could be observed. Low concentrations of F360-InP:Zn MSC produced narrowly distributed QDs due to the In-ODPA complex effect. However, for large amounts, more MSCs yielded smaller and more broadly size-distributed QDs by competitive precursor consumption. For an excessively large amount, MSCs prevailed over QD nucleation and completely blocked QD production. Understanding the roles of MSCs as precursors for QDs will pave the way for sophisticated synthesis design for high-quality QDs.