title: Growth of textured thin Au coatings on iron oxide nanoparticles with near infrared absorbance.
abstract: A homologous series of Au coated iron oxide nanoparticles with hydrodynamic diameters smaller than 60 nm was synthesized with very low Au-to-iron mass ratios, as low as 0.15. The hydrodynamic diameter was determined by dynamic light scattering and the composition by atomic absorption spectroscopy and energy dispersive x-ray spectroscopy. Unusually low Au precursor supersaturation levels were utilized to nucleate and grow Au coatings on iron oxide relative to the formation of pure Au nanoparticles. This approach produced unusually thin coatings by lowering autocatalytic growth of Au on Au, as shown by transmission electron microscopy. Nearly all of the nanoparticles were attracted by a magnet, indicating a minimal number of pure Au particles. The coatings were sufficiently thin to shift the surface plasmon resonance to the near infrared with large extinction coefficients, despite the small particle hydrodynamic diameters observed from dynamic light scattering to be less than 60 nm.
authors.affiliation: Department of Chemical Engineering, University of Texas at Austin, Austin, TX 78712, USA.
authors.forename: L L
authors.initials: LL
authors.lastname: Ma
authors.forename: A U
authors.initials: AU
authors.lastname: Borwankar
authors.forename: B W
authors.initials: BW
authors.lastname: Willsey
authors.forename: K Y
authors.initials: KY
authors.lastname: Yoon
authors.forename: J O
authors.initials: JO
authors.lastname: Tam
authors.forename: K V
authors.initials: KV
authors.lastname: Sokolov
authors.forename: M D
authors.initials: MD
authors.lastname: Feldman
authors.forename: T E
authors.initials: TE
authors.lastname: Milner
authors.forename: K P
authors.initials: KP
authors.lastname: Johnston
mesh_terms: D000042:Absorption; D000327:Adsorption; D003460:Crystallization / Q000379:methods*; D006046:Gold / Q000737:chemistry*; D007259:Infrared Rays; D046911:Macromolecular Substances / Q000737:chemistry; D058185:Magnetite Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure*; D008422:Materials Testing; D008968:Molecular Conformation; D010316:Particle Size; D013499:Surface Properties
chemical_list: D046911:Macromolecular Substances; D058185:Magnetite Nanoparticles; D006046:Gold