DNP-Enhanced 113Cd Solid-State Nuclear Magnetic Resonance Spectroscopy Reveals Tetrahedral CdSe Nanocrystals are Terminated by {100} Facets

Given the important role of surface structure in particle growth and determining the chemical and photophysical properties of NCs, there is a need for structural tools that can characterize and detect different surface facets. Here, we sought to investigate the structure of {111} CdSe facets by applying DNP-enhanced 113Cd and 77Se SSNMR spectroscopy to tetrahedral CdSe NCs. A number of prior studies have demonstrated the synthesis of tetrahedral CdSe NCs, with the particle shapes confirmed by TEM imaging. Surprisingly, we observe 113Cd NMR spectra indicating that facets from the {100} family of lattice planes were present on these particles. We also obtained DNP-enhanced 113Cd and 77Se SSNMR spectra of recently reported right trigonal bipyramidal (RTB) CdSe NCs and also observed 113Cd NMR signature consistent with {100} surface facets. Based upon these results, we conclude that NCs synthesized by routes reported to yield tetrahedral nanocrystals yield {100} terminated tetrahedral shaped particles. TEM images suggest that RTB NCs may also be present. These results highlight the need for multiple complementary techniques when determining the shapes of nanocrystals.