title: Self-assembled simple hexagonal AB(2) binary nanocrystal superlattices: SEM, GISAXS, and defects.
abstract: Binary superlattices (BSLs) of sterically stabilized, hydrophobic, large (A; 11.5 nm diameter) Fe(2)O(3) and small (B; 6.1 nm diameter) Au nanocrystals were assembled by slow evaporation of colloidal dispersions on tilted substrates. A detailed analysis of the BSL structure was carried out using transmission and scanning electron microscopy (TEM and SEM) and grazing incidence small-angle X-ray scattering (GISAXS). The BSLs were simple hexagonal (sh) AB(2) superlattices (isostructural with the compound AlB(2); space group 191, P6/mmm) of large nanocrystals occupying a simple hexagonal lattice with small nanocrystals in the interstitial spaces. SEM and GISAXS confirmed long-range order of the BSLs and GISAXS revealed that the superlattice is slightly contracted (8-12%) perpendicular to the substrate as a result of solvent drying in the deposition process. When the sh-AB(2) superlattice deposits on a (100) plane, this shrinkage occurs in the [210] direction and changes the lattice symmetry to centered orthorhombic. Additionally, nearly periodic superlattice dislocations consisting of inserted half-planes of gold nanocrystals were observed by SEM in some BSLs.
authors.affiliation: Department of Chemical Engineering, Texas Materials Institute, Center for Nano- and Molecular Science and Technology, The University of Texas at Austin, Austin, Texas 78712-1062, USA.
authors.forename: Danielle K
authors.initials: DK
authors.lastname: Smith
authors.forename: Brian
authors.initials: B
authors.lastname: Goodfellow
authors.forename: Detlef-M
authors.initials: DM
authors.lastname: Smilgies
authors.forename: Brian A
authors.initials: BA
authors.lastname: Korgel
mesh_terms: D003102:Colloids / Q000138:chemical synthesis / Q000737:chemistry; D005290:Ferric Compounds / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D049329:Nanostructures / Q000737:chemistry*; D010316:Particle Size; D053838:Scattering, Small Angle; D013499:Surface Properties; D014961:X-Ray Diffraction
chemical_list: D003102:Colloids; D005290:Ferric Compounds; C000499:ferric oxide; D006046:Gold