HAADF-STEM for the analysis of core–shell quantum dots

Abstract

The capability of the imaging technique of high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) to detect the interface in small core/shell quantum dots (QDs) is investigated. In particular, two methodologies based on HAADF-STEM-simulated images are evaluated. The first methodology relies on quantifying the HAADF-STEM intensity variations in the particle to be correlated with the atomic number (Z) changes through the interface core–shell. The second approach consists of the measurement of the strain field of these QDs based on the analysis of the core–shell lattice mismatch. The applicability of both methodologies for core–shell particles of different sell thicknesses and core compositions is discussed. The work has showed that both methodologies are expected to provide successful results as far as the quality of the experimental images is good enough. In addition, both procedures have been applied to an experimental image of CdSe/ZnS colloidal core/shell QD with a nominal value of shell thickness of 0.6 nm, demonstrating the successful detection of the ZnS shell.