title: Ordered two-dimensional superstructures of colloidal octapod-shaped nanocrystals on flat substrates.
abstract: We studied crystal structures in a monolayer consisting of anisotropic branched colloidal (nano)octapods. Experimentally, octapods were observed to form a monolayer on a substrate with a square-lattice crystal structure by drop-casting and fast evaporation of solvent. The experimental results were analyzed by Monte Carlo simulations using a hard octapod model consisting of four interpenetrating spherocylinders. We confirmed by means of free-energy calculations that crystal structures with a (binary-lattice) square morphology are indeed thermodynamically stable at high densities. The effect of the pod length-to-diameter ratio on the crystal structures was also considered and we used this to constructed the phase diagram for these hard octapods. In addition to the (binary-lattice) square crystal phase, a rhombic crystal and a hexagonal plastic-crystal (rotator) phase were obtained. Our phase diagram may prove instrumental in guiding future experimental studies.
authors.affiliation: Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands. W.Qi@uu.nl
authors.forename: Weikai
authors.initials: W
authors.lastname: Qi
authors.forename: Joost
authors.initials: J
authors.lastname: de Graaf
authors.forename: Fen
authors.initials: F
authors.lastname: Qiao
authors.forename: Sergio
authors.initials: S
authors.lastname: Marras
authors.forename: Liberato
authors.initials: L
authors.lastname: Manna
authors.forename: Marjolein
authors.initials: M
authors.lastname: Dijkstra