Pulsed axial epitaxy of colloidal quantum dots in nanowires enables facet-selective passivation

Yi Li,Tao-Tao Zhuang,Yun-Xiang Pan,Haiming Zhu,Fengjia Fan,Guo-Qiang Liu,Oleksandr Voznyy,Mikhail Askerka,Liang Wu,Shu-Hong Yu,Edward H Sargent

doi:10.1038/s41467-018-07422-4

Abstract

Epitaxially stacking colloidal quantum dots in nanowires offers a route to selective passivation of defective facets while simultaneously enabling charge transfer to molecular adsorbates – features that must be combined to achieve high-efficiency photocatalysts. This requires dynamical switching of precursors to grow, alternatingly, the quantum dots and nanowires – something not readily implemented in conventional flask-based solution chemistry. Here we report pulsed axial epitaxy, a growth mode that enables the stacking of multiple CdS quantum dots in ZnS nanowires. The approach relies on the energy difference of incorporating these semiconductor atoms into the host catalyst, which determines the nucleation sequence at the catalyst-nanowire interface. This flexible synthetic strategy allows precise modulation of quantum dot size, number, spacing, and crystal phase. The facet-selective passivation of quantum dots in nanowires opens a pathway to photocatalyst engineering: we report photocatalysts that exhibit an order-of-magnitude higher photocatalytic hydrogen evolution rates than do plain CdS quantum dots.

Highlights

Stacking colloidal quantum dots in nanowires offers a route to selective passivation of defective facets while simultaneously enabling charge transfer to molecular adsorbates – features that must be combined to achieve high-efficiency photocatalysts
In a catalyst-assisted growth process, the growth of semiconductor nanowires can be switched by injecting precursors for quantum dots, which are incorporated into the host catalyst and nucleate first at the catalyst-nanowire interface
We found that CdS quantum dots (QDs) are incorporated into ZnS nanowires with substantially equal spacing, a finding that is further confirmed using dark-field scanning transmission electron microscopy (TEM) (STEM) images (Fig. 2d–f and Supplementary Fig. 8)

Summary

Introduction

Stacking colloidal quantum dots in nanowires offers a route to selective passivation of defective facets while simultaneously enabling charge transfer to molecular adsorbates – features that must be combined to achieve high-efficiency photocatalysts. We term this one-pot synthetic strategy pulsed axial epitaxial growth (PAEG), highlighting its ability to modulate the stacking of multiple CdS QDs in ZnS nanowires by controlling the pulsed introduction of the Cd precursor.

Results

Conclusion