Internal Atomic-Scale Structure Determination and Band Alignment of II–VI Quantum Dot Heterostructures

Abstract

This work shows that ZnTe/CdSe core/shell quantum dots synthesized by a standard literature procedure in actuality have an alloyed CdxZn1–xTe core. We employ X-ray absorption spectroscopy (XAS) at all four K-shell ionization edges (Zn, Te, Cd, and Se) and perform global fitting analysis to extract the first-shell bond distances. We combine our XAS results with transmission electron microscopy (TEM) sizing and elemental analyses, which allows us to propose models of the internal particle structure. Our multimodal characterization approach confirms (1) the presence of Cd–Te bonds, (2) cation alloying in the particle core (and the absence of anion alloying), and (3) a patchy pure-phase CdSe shell. We synthesize particles of different shell thicknesses and performed synthetic control studies that allowed us to discard a ZnTe/CdTe/CdSe core/shell/shell structure and confirm the alloyed core/shell structure. Our structural analysis is extended with electronic band structure calculations and UV/vis absorption sp...