title: Sequential cation exchange in nanocrystals: preservation of crystal phase and formation of metastable phases.
abstract: We demonstrate that it is possible to convert CdSe nanocrystals of a given size, shape (either spherical or rod shaped), and crystal structure (either hexagonal wurtzite, i.e., hexagonal close packed (hcp), or cubic sphalerite, i.e., face-centered cubic (fcc)), into ZnSe nanocrystals that preserve all these characteristics of the starting particles (i.e., size, shape, and crystal structure), via a sequence of two cation exchange reactions, namely, Cd(2+) ⇒Cu(+) ⇒Zn(2+). When starting from hexagonal wurtzite CdSe nanocrystals, the exchange of Cd(2+) with Cu(+) yields Cu(2)Se nanocrystals in a metastable hexagonal phase, of which we could follow the transformation to the more stable fcc phase for a single nanorod, under the electron microscope. Remarkably, these metastable hcp Cu(2)Se nanocrystals can be converted in solution into ZnSe nanocrystals, which yields ZnSe nanocrystals in a pure hcp phase.
authors.affiliation: Istituto Italiano di Tecnologia, via Morego 30, 16163 Genova, Italy.
authors.forename: Hongbo
authors.initials: H
authors.lastname: Li
authors.forename: Marco
authors.initials: M
authors.lastname: Zanella
authors.forename: Alessandro
authors.initials: A
authors.lastname: Genovese
authors.forename: Mauro
authors.initials: M
authors.lastname: Povia
authors.forename: Andrea
authors.initials: A
authors.lastname: Falqui
authors.forename: Cinzia
authors.initials: C
authors.lastname: Giannini
authors.forename: Liberato
authors.initials: L
authors.lastname: Manna
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D002412:Cations; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D044367:Phase Transition; D018036:Selenium Compounds / Q000737:chemistry*
chemical_list: D019187:Cadmium Compounds; D002412:Cations; D018036:Selenium Compounds; C058667:cadmium selenide