General low-temperature reaction pathway from precursors to monomers before nucleation of compound semiconductor nanocrystals.

Xiangyang Liu,Changwei Hu,Kui Yu,Huaqing Yang,Dennis M Whitfield,Erik J C Huisman,Ting Qi,Queena Y Chen

doi:10.1038/ncomms12223

Abstract

Little is known about the molecular pathway to monomers of semiconductor nanocrystals. Here we report a general reaction pathway, which is based on hydrogen-mediated ligand loss for the precursor conversion to ‘monomers' at low temperature before nucleation. We apply 31P nuclear magnetic resonance spectroscopy to monitor the key phosphorous-containing products that evolve from MXn+E=PPh2H+HY mixtures, where MXn, E=PPh2H, and HY are metal precursors, chalcogenide precursors, and additives, respectively. Surprisingly, the phosphorous-containing products detected can be categorized into two groups, Ph2P–Y and Ph2P(E)–Y. On the basis of our experimental and theoretical results, we propose two competing pathways to the formation of M2En monomers, each of which is accompanied by one of the two products. Our study unravels the pathway of precursor evolution into M2En monomers, the stoichiometry of which directly correlates with the atomic composition of the final compound nanocrystals.

Highlights

Little is known about the molecular pathway to monomers of semiconductor nanocrystals
The in-depth interpretation of the mechanism is supported by our density functional theory (DFT) calculations
HY participates in the formation of monomers and could accelerate nucleation; a large amount of HY plays the role of a solvent and, could retard nucleation

Summary

Introduction

Little is known about the molecular pathway to monomers of semiconductor nanocrystals. A major advance in the NC synthesis occurred with the recognition that commercial tertiary phosphine TOP contains dioctylphosphine (HP(C8H17)[2], a secondary phosphine) that acts as an active impurity facilitating NC nucleation/growth but leading to low synthetic reproducibility (because of its varying amount from batch to batch)[13,14,15,23] It was first suggested[15] and experimentally demonstrated[23] that the use of commercial diphenylphosphine (HP(C6H5)[2] or HPPh2, a secondary phosphine) resulted in an equilibrium of SeTOP þ HPPh2" TOP þ Se1⁄4PPh2H. We propose two competing pathways leading to M2En monomers as illustrated by equations 1 and 2 (with further explanation in equations 3–6)

Methods

Results

Conclusion