Direct Three-Dimensional Observation of Core/Shell-Structured Quantum Dots with a Composition-Competitive Gradient

Synthesizing semiconductor nanoparticles through core/shell structuring is an effective strategy to promote the functional, physical, and kinetic performance of optoelectronic materials. However, elucidating the internal structure and related atomic distribution of core/shell structured quantum dots (QDs) in three dimensions, particularly at heterostructure interfaces, has been an overarching challenge. Herein, by applying complementary analytical techniques of electron microscopy and atom probe tomography, the dimensional, structural, topological, and compositional information on commercially available 11.8 nm-sized CdSSe/ZnS QDs were obtained. Systematic experiments at high resolution reveal the presence of a 1.8 nm-thick CdxZn1–xS inner shell with a composition gradient between the CdSe core and the ZnS outermost shell. More strikingly, the inner shell shows compositional variation because of competitive atomic configuration between Cd and ZnS, but it structurally retains a zinc-blende crystal structur...