title: Ligand-controlled polytypism of thick-shell CdSe/CdS nanocrystals.
abstract: We report the synthesis of CdSe/CdS semiconductor core/shell nanocrystals with very thick (5 nm) CdS shells. As in the case of core CdSe nanocrystals, we show that a thick-shell CdSe/CdS core/shell structure can be synthesized in either a pure wurtzite (W) or a zinc-blende (ZB) crystal structure. While the growth of thick-shell wurtzite CdSe/CdS is quite straightforward, we observe that the growth of a CdS shell on zinc-blende CdSe cores is more difficult and leads to wurtzite/zinc-blende polytypism when primary amines are present during the shell formation. Using absorption spectra analysis to differentiate zinc blende from wurtzite CdSe, we show that primary amines can induce a nearly complete structural transformation of CdSe ZB cores into W cores. This better understanding of the CdSe ligand-dependent crystal structural evolution during shell growth is further used to grow large (10 nm)-diameter perfect zinc-blende CdSe core crystals emitting above 700 nm, and perfect ZB thick-shell CdSe/CdS nanocrystals. We observed that all thick-shell CdSe/CdS QDs have extremely reduced blinking events compared to thin-shell QDs, without any significant influence of crystalline structure and polytypism.
authors.affiliation: Laboratoire de Physique et d'Etude des Matériaux, CNRS UPR5, ESPCI 10 rue Vauquelin, 75231 Paris, France.
authors.forename: Benoît
authors.initials: B
authors.lastname: Mahler
authors.forename: Nicolas
authors.initials: N
authors.lastname: Lequeux
authors.forename: Benoît
authors.initials: B
authors.lastname: Dubertret
mesh_terms: D019187:Cadmium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D008024:Ligands; D049329:Nanostructures / Q000737:chemistry*; D010316:Particle Size; D018036:Selenium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D012666:Semiconductors; D013440:Sulfides / Q000138:chemical synthesis / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D019187:Cadmium Compounds; D008024:Ligands; D018036:Selenium Compounds; D013440:Sulfides; C034939:cadmium sulfide; C058667:cadmium selenide