title: Structural order in ultrathin films of the monolayer protected clusters based upon 4 nm gold nanocrystals: an experimental and theoretical study.
abstract: The structural order in ultrathin films of monolayer protected clusters (MPCs) is important in a number of application areas but can be difficult to demonstrate by conventional methods, particularly when the metallic core dimension, d, is in the intermediate size-range, 1.5 < d < 5.0 nm. Here, improved techniques for the synthesis of monodisperse thiolate-protected gold nanoparticles have made possible the production of dodecane-thiolate saturated ∼4 ± 0.5 nm Au clusters with single-crystal core structure and morphology. An ultrathin ordered film or superlattice of these nanocrystal-core MPCs is prepared and investigated using aberration corrected scanning/transmission electron microscopy (STEM) which allowed imaging of long-range hexagonally ordered superlattices of the nanocrystals, separated by the thiolate groups. The lattice constants determined by direct imaging are in good agreement with those determined by small-angle electron diffraction. The STEM image revealed the characteristic grain boundary (GB) with sigma (Σ) 13 in the interface between two crystals. The formation and structures found are interpreted on the basis of theoretical calculations employing molecular dynamics (MD) simulations and coarse-grained (CG) approach.
authors.affiliation: Department of Physics and Astronomy, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA. miguel.yacaman@utsa.edu.
authors.forename: Nabraj
authors.initials: N
authors.lastname: Bhattarai
authors.forename: Subarna
authors.initials: S
authors.lastname: Khanal
authors.forename: Daniel
authors.initials: D
authors.lastname: Bahena
authors.forename: Jimena A
authors.initials: JA
authors.lastname: Olmos-Asar
authors.forename: Arturo
authors.initials: A
authors.lastname: Ponce
authors.forename: Robert L
authors.initials: RL
authors.lastname: Whetten
authors.forename: Marcelo M
authors.initials: MM
authors.lastname: Mariscal
authors.forename: Miguel
authors.initials: M
authors.lastname: Jose-Yacaman
mesh_terms: D003198:Computer Simulation; D003460:Crystallization / Q000379:methods; D006046:Gold / Q000737:chemistry*; D008422:Materials Testing; D008567:Membranes, Artificial; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure*; D008956:Models, Chemical; D008958:Models, Molecular; D053761:Nanocomposites / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size
chemical_list: D008567:Membranes, Artificial; D006046:Gold