Statistical Description of CdSe/CdS Dot-in-Rod Heterostructures Using Scanning Transmission Electron Microscopy

Annular dark-field scanning transmission electron microscopy (ADF-STEM) is employed to provide a statistical description of faceting, core location, stacking faults, and polar self-assembly behavior of CdSe/CdS dot-in-rod heterostructures. Applied to dot-in-rod and rod-in-rod heterostructures, STEM enables statistical measurements of core locations that show that the position of the CdSe core lies at ≈45% of the length of the sample, slightly closer to the blunt (001) facet of the CdS nanorod shell. A study of stacking faults reveals a substantially enhanced probability near the epitaxial interface of the core and shell, suggesting the role of epitaxial strain in the formation of defects. Structural analysis is extended to liquid-crystalline monolayers of nanorods, and the role of dipolar interactions within lamellae is analyzed using one-dimensional pair-distribution analysis of polarity, showing that the nanorods have a random dipole alignment.