Surface structure plays an important role in particle growth and determining the chemical and photophysical properties of semiconductor nanocrystals (NCs). Therefore, 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 dynamic nuclear polarization (DNP) enhanced 113Cd and 77Se solid-state nuclear magnetic resonance (SSNMR) spectroscopy to zinc-blende CdSe NCs that exhibit triangular two-dimensional (2D) projections within transmission electron microscope (TEM) images. It was originally hypothesized in the literature that these CdSe NCs were tetrahedral in shape and terminated by facets from the 111 family of lattice planes of the zinc-blende structure. Surprisingly, we observe 113Cd NMR spectra indicating that the primary facets are from the 100 family of lattice planes. We also obtained DNP-enhanced 113Cd and 77Se SSNMR spectra of recently reported right trigonal bipyramidal (rTriBP) CdSe NCs grown by seeded growth. The 113Cd NMR spectra rTriBP CdSe NCs are consistent with 100 surface facets. TEM images show that rTriBP NCs may also exhibit triangular 2D projections that are similar to the so-called tetrahedral NCs. Based upon these results, we conclude that the so-called tetrahedral NCs are predominantly terminated by 100 surface facets and most likely have the same shape as rTriBP NCs. These results highlight the need for multiple complementary techniques when assigning the shape and surface termination of NCs.
Santhiran et al. (Fri,) studied this question.