Point group assignment of CdSe nanocrystals

We have used High Resolution Transmission Electron Microscopy (HRTEM) to investigate the morphology of chemically synthesized CdSe nanocrystals (mean diameters ranging from 2nm to 7nm). CdSe nanocrystals have been the subject of much experimental and theoretical scrutiny and are rapidly becoming the prototypical system for the study of quantum confinement effects. Spectral assignments and theoretical calculations are usually performed under the assumption that these nanocrystals are spherical in shape. HRTEM lattice resolution images allow determination of the actual, three-dimensional shape of these crystallites. We find that these crystallites have a distinct, non-spherical morphology which allows us to assign these nanocrystals to the C{sub 3v} point goup. We relate structure to the optical properties using Resonance Raman Depolarization (RRD) spectroscopy. The RRD data are consistent with the HRTEM structural assignment and are inconsistent with spherical symmetry.