title: Molecular control of the nanoscale: effect of phosphine-chalcogenide reactivity on CdS-CdSe nanocrystal composition and morphology.
abstract: We demonstrate molecular control of nanoscale composition, alloying, and morphology (aspect ratio) in CdS-CdSe nanocrystal dots and rods by modulating the chemical reactivity of phosphine-chalcogenide precursors. Specific molecular precursors studied were sulfides and selenides of triphenylphosphite (TPP), diphenylpropylphosphine (DPP), tributylphosphine (TBP), trioctylphosphine (TOP), and hexaethylphosphorustriamide (HPT). Computational (DFT), NMR ((31)P and (77)Se), and high-temperature crossover studies unambiguously confirm a chemical bonding interaction between phosphorus and chalcogen atoms in all precursors. Phosphine−chalcogenide precursor reactivity increases in the order: HPTE < TOPE < TBPE < DPPE <TPPE (E = S < Se). For a given phosphine, the selenide is always more reactive than the sulfide. CdS(1-x)Se(x) quantum dots were synthesized via single injection of a R(3)PS-R(3)PSe mixture to cadmium oleate at 250 °C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV/Vis and PL optical spectroscopy reveal that relative R(3)PS and R(3)PSe reactivity dictates CdS(1-x)Se(x) dot chalcogen content and the extent of radial alloying (alloys vs core/shells). CdS, CdSe, and CdS(1-x)Se(x) quantum rods were synthesized by injection of a single R(3)PE (E = S or Se) precursor or a R(3)PS-R(3)PSe mixture to cadmium-phosphonate at 320 or 250 °C. XRD and TEM reveal that the length-to-diameter aspect ratio of CdS and CdSe nanorods is inversely proportional to R(3)PE precursor reactivity. Purposely matching or mismatching R(3)PS-R(3)PSe precursor reactivity leads to CdS(1-x)Se(x) nanorods without or with axial composition gradients, respectively. We expect these observations will lead to scalable and highly predictable "bottom-up" programmed syntheses of finely heterostructured nanomaterials with well-defined architectures and properties that are tailored for precise applications [corrected].
authors.affiliation: Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: T Purnima A
authors.initials: TP
authors.lastname: Ruberu
authors.forename: Haley R
authors.initials: HR
authors.lastname: Albright
authors.forename: Brandon
authors.initials: B
authors.lastname: Callis
authors.forename: Brittney
authors.initials: B
authors.lastname: Ward
authors.forename: Joana
authors.initials: J
authors.lastname: Cisneros
authors.forename: Hua-Jun
authors.initials: HJ
authors.lastname: Fan
authors.forename: Javier
authors.initials: J
authors.lastname: Vela
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D018011:Chalcogens / Q000737:chemistry*; D008422:Materials Testing; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D010720:Phosphines / Q000737:chemistry*; D018036:Selenium Compounds / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry*
chemical_list: D019187:Cadmium Compounds; D018011:Chalcogens; D010720:Phosphines; D018036:Selenium Compounds; D013440:Sulfides; C034939:cadmium sulfide; C058667:cadmium selenide; C044646:phosphine