title: Role of Halides in the Ordered Structure Transitions of Heated Gold Nanocrystal Superlattices.
abstract: Dodecanethiol-capped gold (Au) nanocrystal superlattices can undergo a surprisingly diverse series of ordered structure transitions when heated (Goodfellow, B. W.; Rasch, M. R.; Hessel, C. M.; Patel, R. N.; Smilgies, D.-M.; Korgel, B. A. Nano Lett. 2013, 13, 5710-5714). These are the result of highly uniform changes in nanocrystal size, which subsequently force a spontaneous rearrangement of superlattice structure. Here, we show that halide-containing surfactants play an essential role in these transitions. In the absence of any halide-containing surfactant, superlattices of dodecanethiol-capped (1.9-nm-diameter) Au nanocrystals do not change size until reaching about 190-205 °C, at which point the gold cores coalesce. In the presence of halide-containing surfactant, such as tetraoctylphosphonium bromide (TOPB) or tetraoctylammounium bromide (TOAB), the nanocrystals ripen at much lower temperature and superlattices undergo various ordered structure transitions upon heating. Chloride- and iodide-containing surfactants induce similar behavior, destabilizing the Au-thiol bond and reducing the thermal stability of the nanocrystals.
authors.affiliation: †McKetta Department of Chemical Engineering, Texas Materials Institute and Center for Nano- and Molecular Science and Technology, The University of Texas at Austin, Austin, Texas 78712-1062, United States.
authors.forename: Yixuan
authors.initials: Y
authors.lastname: Yu
authors.affiliation: †McKetta Department of Chemical Engineering, Texas Materials Institute and Center for Nano- and Molecular Science and Technology, The University of Texas at Austin, Austin, Texas 78712-1062, United States.
authors.forename: Brian W
authors.initials: BW
authors.lastname: Goodfellow
authors.affiliation: †McKetta Department of Chemical Engineering, Texas Materials Institute and Center for Nano- and Molecular Science and Technology, The University of Texas at Austin, Austin, Texas 78712-1062, United States.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Rasch
authors.affiliation: †McKetta Department of Chemical Engineering, Texas Materials Institute and Center for Nano- and Molecular Science and Technology, The University of Texas at Austin, Austin, Texas 78712-1062, United States.
authors.forename: Christian
authors.initials: C
authors.lastname: Bosoy
authors.affiliation: ‡Cornell High Energy Synchrotron Source (CHESS), Cornell University, Ithaca, New York 14853, United States.
authors.forename: Detlef-M
authors.initials: DM
authors.lastname: Smilgies
authors.affiliation: †McKetta Department of Chemical Engineering, Texas Materials Institute and Center for Nano- and Molecular Science and Technology, The University of Texas at Austin, Austin, Texas 78712-1062, United States.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Korgel