Single-charge transport through hybrid core-shell Au-ZnS quantum dots : A comprehensive analysis from the modified energy structure

Abstract

We examine the modified electronic structure and single-carrier transport of individual hybrid core-shell metal-semiconductor Au-ZnS quantum dots (QDs) by a scanning tunnel microscope. Nearly monodisperse ultra-small QDs are achieved by a facile wet chemical route. The exact energy structures are evaluated by scanning tunneling spectroscopy (STS) measurements at 300 mK for the individual nanoobjects starting from the main building block Au nanocrystals (NCs) to the final Au-ZnS QDs. The study divulges the evolution of the energy structure and the charge transport from the single metallic building block core to the core-shell metal-semiconductor QD. Further, we successfully determine the contributions related to the quantum-confinement-induced excitonic band structure of the ZnS nano-shell and the charging energy of the system by applying a semi-empirical approach considering a double barrier tunnel junction (DBTJ) arrangement. We detect strong conductance peaks in an Au-ZnS QD due to the overlapping of the energy structure of the Au nano-core and the discrete energy states of the semiconductor ZnS nano-shell. Our findings will help to understand the electronic properties of metal-semiconductor QDs. The outcomes, therefore, have the potential to fabricate tailored metal-semiconductor QDs for single-electron devices.