Fig. 2.

Surface facet chemistry of ionic nanocrystals with zinc blende (ZB) or wurtzite (WZ) crystal phases, showing CdSe examples. (a,b) Bonding geometries and structures of ZB and WZ QDs. From left to right: crystal phase unit vectors, unit cell, two views of the internal bonding geometry parallel to, and perpendicular to, the [111]_ZB and [0001]_WZ direction, and two schematics of nanocrystals indicating atomic locations and lattice facet identifications. Cd²⁺ ions are grey and Se²⁻ ions are orange. (c,d) Surface facets are depicted from two orientations (side and top views). As shown, they are “bare” without ligands and without reconstruction. Dangling bonds (DBs) are shown indicating whether they are electron-rich on Se²⁻ or electron-poor on Cd²⁺. (c) Charged facets have either cationic Cd²⁺-rich surfaces or anionic Se²⁻-rich surfaces (only cation-rich surfaces are shown). (d) Neutral facets have equal numbers of cations and anions. (e) Transmission electron micrographs of four nanocrystals are shown with different facets exposed, showing QDs with all {100}_ZB, all {111}_ZB, all {112̄0}_WZ, or mixed facets (reproduced from references [27] and [28] with permission).