Obtaining Structural Parameters from STEM-EDX Maps of Core/Shell Nanocrystals for Optoelectronics

Characterization efforts of core/shell and core/multishell nanocrystals have struggled to quantitatively evaluate the interface width between the core and shell materials despite its importance in their optoelectronic properties. Here, we demonstrate a scanning transmission electron microscopy (STEM) method for measuring the radial elemental composition of two spherical core/shell nanocrystal systems, Ge/Si core/shell and CdSe/CdS/ZnS core/double-shell nanocrystals. By fitting model-based radial distributions of elements to measured STEM-energy-dispersive X-ray (EDX) maps, this method yields reliable and accurate measurements of interface broadening as well as core and shell sizes, surface roughness, and the fraction of core material in the shell. The direct evaluation of the structural parameters is an important step toward improving the synthesis of core/shell nanocrystals and optimizing their optoelectronic properties.