Probing intermediates of the induction period prior to nucleation and growth of semiconductor quantum dots

Mingyang Liu,Kun Wang,Romain Renoud,Kui Yu,Nelson Rowell,Fenggang Bian,Shuo Han,Hongsong Fan,Jianrong Zeng,John A Ripmeester,Linxi Wang

doi:10.1038/ncomms15467

Abstract

Little is known about the induction period before the nucleation and growth of colloidal semiconductor quantum dots. Here, we introduce an approach that allows us to probe intermediates present in the induction period. We show that this induction period itself exhibits distinct stages with the evolution of the intermediates, first without and then with the formation of covalent bonds between metal cations and chalcogenide anions. The intermediates are optically invisible in toluene, while the covalent-bonded intermediates become visible as magic-size clusters when a primary amine is added. Such evolution of magic-size clusters provides indirect but compelling evidence for the presence of the intermediates in the induction period and supports the multi-step nucleation model. Our study reveals that magic-size clusters could be readily engineered in a single-size form, and suggests that the existence of the intermediates during the growth of conventional quantum dots results in low product yield.

Highlights

Little is known about the induction period before the nucleation and growth of colloidal semiconductor quantum dots
To explore the species that evolved in the induction period and their possible presence after nucleation/growth of regular QDs (RQDs), the Cd and Te precursors were mixed at 135 °C; the reaction mixture was kept at this temperature for a variable length of reaction time from 1 to 90 min
In the study presented here, we show that we have effectively decoupled the complex reaction stages and achieved the stabilization of two Intermediates, denoted as 1 and 2, which we hypothesize to be formed during the induction period before the nucleation and growth of RQDs

Summary

Introduction

Little is known about the induction period before the nucleation and growth of colloidal semiconductor quantum dots. The intermediates are optically invisible in toluene, while the covalent-bonded intermediates become visible as magic-size clusters when a primary amine is added Such evolution of magic-size clusters provides indirect but compelling evidence for the presence of the intermediates in the induction period and supports the multi-step nucleation model. A number of synthetic approaches have been documented that typically involved a laborious trial-and-error scheme to produce colloidal semiconductor CdTe (refs 31–34), CdSe (refs 34–42), CdS (refs 43,44) and other composition MSCs45–48. These studies did not address the formation pathway of the MSCs, some did propose that the MSCs were the actual nuclei for the growth of NCs13,38,43,47. The coexistence of MSCs of several sizes (instead of a single size) with a single CdE RQD ensemble in one reaction batch does not support such an Intermediate 1

Methods

Results

Conclusion