title: Structure/processing relationships of highly ordered lead salt nanocrystal superlattices.
abstract: We investigated the influence of processing conditions, nanocrystal/substrate interactions and solvent evaporation rate on the ordering of strongly interacting nanocrystals by synergistically combining electron microscopy and synchrotron-based small-angle X-ray scattering analysis. Spin-cast PbSe nanocrystal films exhibited submicrometer-sized supracrystals with face-centered cubic symmetry and (001)(s) planes aligned parallel to the substrate. The ordering of drop-cast lead salt nanocrystal films was sensitive to the nature of the substrate and solvent evaporation dynamics. Nanocrystal films drop-cast on rough indium tin oxide substrates were polycrystalline with small grain size and low degree of orientation with respect to the substrate, whereas films drop-cast on flat Si substrates formed highly ordered face-centered cubic supracrystals with close-packed (111)(s) planes parallel to the substrate. The spatial coherence of nanocrystal films drop-cast in the presence of saturated solvent vapor was significantly improved compared to films drop-cast in a dry environment. Solvent vapor annealing was demonstrated as a postdeposition technique to modify the ordering of nanocrystals in the thin film. Octane vapor significantly improved the long-range order and degree of orientation of initially disordered or polycrystalline nanocrystal assemblies. Exposure to 1,2-ethanedithiol vapor caused partial displacement of surface bound oleic acid ligands and drastically degraded the degree of order in the nanocrystal assembly.
authors.affiliation: School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA. th358@cornell.edu
authors.forename: Tobias
authors.initials: T
authors.lastname: Hanrath
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Choi
authors.forename: Detlef-M
authors.initials: DM
authors.lastname: Smilgies
mesh_terms: D004058:Diffusion; D007854:Lead / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry*; D012492:Salts / Q000737:chemistry*; D053838:Scattering, Small Angle; D018036:Selenium Compounds / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013440:Sulfides / Q000737:chemistry; D013997:Time Factors; D014835:Volatilization; D014961:X-Ray Diffraction
chemical_list: D012492:Salts; D018036:Selenium Compounds; D012997:Solvents; D013440:Sulfides; C088065:lead selenide; C018391:lead sulfide; D007854:Lead