title: Reduced Ensemble Plasmon Line Widths and Enhanced Two-Photon Luminescence in Anodically Formed High Surface Area Au-TiO23D Nanocomposites.
abstract: Localized surface plasmon resonances (LSPR) in TiO2nanorod and nanotube arrays decorated by gold nanoparticles can be exploited to improve photocatalytic activity, enhance nonlinear optical coefficients, and increase light harvesting in solar cells. However, the LSPR typically has a low quality factor, and the resonance is often obscured by the Urbach tail of the TiO2band gap absorption. Attempts to increase the LSPR extinction intensity by increasing the density of gold nanoparticles on the surface of the TiO2nanostructures invariably produce peak broadening due to the effects of either agglomeration or polydispersity. We present a new class of hybrid nanostructures containing gold nanoparticles (NPs) partially embedded in nanoporous/nanotubular TiO2by performing the anodization of cosputtered Ti-Au thin films containing a relatively high ratio of Au:Ti. Our method of anodizing thin film stacks containing alternate layers of Ti and TiAu results in very distinctive LSPR peaks with quality factors as high as 6.9 and ensemble line widths as small as 0.33 eV even in the presence of an Urbach tail. Unusual features in the anodization of such films are observed and explained, including oscillatory current transients and the observation of coherent heterointerfaces between the Au NPs and anatase TiO2. We further show that such a plasmonic NP-embedded nanotube structure dramatically outperforms a plasmonic NP-decorated anodic nanotube structure in terms of the extinction coefficient, and achieves a strongly enhanced two-photon fluorescence due to the high density of gold nanoparticles in the composite film and the plasmonic local field enhancement.
authors.affiliation: Department of Electrical and Computer Engineering, University of Alberta , 9211-116 Street, Edmonton, Alberta T6G 1H9, Canada.
authors.forename: Samira
authors.initials: S
authors.lastname: Farsinezhad
authors.affiliation: Department of Electrical and Computer Engineering, University of Alberta , 9211-116 Street, Edmonton, Alberta T6G 1H9, Canada.
authors.forename: Shyama Prasad
authors.initials: SP
authors.lastname: Banerjee
authors.affiliation: Department of Electrical and Computer Engineering, University of Alberta , 9211-116 Street, Edmonton, Alberta T6G 1H9, Canada.
authors.forename: Bharath
authors.initials: B
authors.lastname: Bangalore Rajeeva
authors.affiliation: Department of Electrical and Computer Engineering, University of Alberta , 9211-116 Street, Edmonton, Alberta T6G 1H9, Canada.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Wiltshire
authors.affiliation: Department of Electrical and Computer Engineering, University of Alberta , 9211-116 Street, Edmonton, Alberta T6G 1H9, Canada.
authors.forename: Himani
authors.initials: H
authors.lastname: Sharma
authors.affiliation: Department of Electrical and Computer Engineering, University of Alberta , 9211-116 Street, Edmonton, Alberta T6G 1H9, Canada.
authors.forename: Anton
authors.initials: A
authors.lastname: Sura
authors.affiliation: Department of Electrical and Computer Engineering, University of Alberta , 9211-116 Street, Edmonton, Alberta T6G 1H9, Canada.
authors.forename: Arash
authors.initials: A
authors.lastname: Mohammadpour
authors.affiliation: Department of Electrical and Computer Engineering, University of Alberta , 9211-116 Street, Edmonton, Alberta T6G 1H9, Canada.
authors.forename: Piyush
authors.initials: P
authors.lastname: Kar
authors.affiliation: Department of Electrical and Computer Engineering, University of Alberta , 9211-116 Street, Edmonton, Alberta T6G 1H9, Canada.
authors.forename: Robert
authors.initials: R
authors.lastname: Fedosejevs
authors.affiliation: Department of Electrical and Computer Engineering, University of Alberta , 9211-116 Street, Edmonton, Alberta T6G 1H9, Canada.|NRC National Institute for Nanotechnology , 11421 Saskatchewan Drive NW, Edmonton, Alberta T6G 2M9, Canada.
authors.forename: Karthik
authors.identifier: http://orcid.org/0000-0001-7347-3333
authors.initials: K
authors.lastname: Shankar
keywords: electrochemical anodization; heterogeneous catalysis; internal electric fields; nonlinear optical media; solar fuels; titania nanotubes