Sublattice resolution structural and chemical analysis of individual CdSe nanocrystals using atomic number contrast scanning transmission electron microscopy and electron energy loss spectroscopy

Atomic number contrast scanning transmission electron microscopy (Z-STEM), with atomic resolution and sub-nanometer resolution scanning transmission electron microscope electron energy loss spectroscopy (STEM-EELS), was used to study single colloidal CdSe semiconductor nanocrystals embedded in MEH-PPV polymer films. The atomic column-resolved Z-STEM image provides information both on the lateral shape of the nanocrystal, as well as the relative thickness of the individual atom columns from a single image. The three-dimensional shape profile reconstructed from the data matches the predicted model. Furthermore, the sublattice is resolved so the polar surfaces can be uniquely identified. Sub-nanometer resolution EELS measurements on an individual nanocrystal indicate the presence of oxygen. The spatial distribution of the oxygen signal in the EELS measurement suggests a thin oxide layer on the nanocrystal surface.