Anisotropic cation exchange of CdSe nanorods into CdSe/PbSe Janus nanorods retaining original morphology

Abstract

Cation exchange is known for its versatility in the design of novel nanocrystals which cannot be synthesized by routine hot-injection or heating-up methods. Here, we report the direct methodology of Cd-to-Pb cation exchange in CdSe nanorods and the role of ligands in cation exchange reaction. While previously reported conversion method of using PbCl2-oleylamine complex led to morphology change of nanorods into spherical nanoparticles, mixture of Pb-oleate and oleylamine triggered anisotropic cation exchange of nanorod with its morphology remains intact. When the mild reaction temperature is given, CdSe/PbSe Janus nanorods with axial heterojunctions were obtained. Microscopic analysis revealed that the cation exchange proceeds asymmetrically along the direction at both tips of CdSe NRs. Binding energy calculation based on density-functional theory revealed that the asymmetry of reaction rate would be caused by strong binding of oleylamine on the (000-1) facet of CdSe nanorods.