title: Electric field enhancement in a self-assembled 2D array of silver nanospheres.
abstract: We investigate the plasmonic properties of a self-assembled 2D array of Ag nanospheres (average particle diameter/inter-particle separation distance of 9/3.7 nm). The structures of the individual particles and their assemblies are characterized using high-resolution transmission electron microscopy (HR-TEM). The plasmonic response of the nanoparticle network is probed using two-photon photoemission electron microscopy (TP-PEEM). HR-TEM and TP-PEEM statistics reveal the structure and plasmonic response of the network to be homogeneous on average. This translates into a relatively uniform surface-enhanced Raman scattering (SERS) response from biphenyl,4-4(')-dithiol (BPDT) molecules adsorbed onto different sites of the network. Reproducible, bright, and low-background SERS spectra are recorded and assigned on the basis of density functional theory calculations in which BPDT is chemisorbed onto the vertex of a finite tetrahedral Ag cluster consisting of 20 Ag atoms. A notable agreement between experiment and theory allows us to rigorously account for the observable vibrational states of BPDT in the ∼200-2200 cm(-1) region of the spectrum. Finite difference time domain simulations further reveal that physical enhancement factors on the order of 10(6) are attainable at the nanogaps formed between the silver nanospheres in the 2D array. Combined with modest chemical enhancement factors, this study paves the way for reproducible single molecule signals from an easily self-assembled SERS substrate.
authors.affiliation: Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Patrick Z
authors.initials: PZ
authors.lastname: El-Khoury
authors.affiliation: Department of Physics and the Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA.
authors.forename: Elena
authors.initials: E
authors.lastname: Khon
authors.affiliation: Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Yu
authors.initials: Y
authors.lastname: Gong
authors.affiliation: Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Alan G
authors.initials: AG
authors.lastname: Joly
authors.affiliation: Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Patricia
authors.initials: P
authors.lastname: Abellan
authors.affiliation: Environ. Molecular Sci. Lab., Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: James E
authors.initials: JE
authors.lastname: Evans
authors.affiliation: Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Nigel D
authors.initials: ND
authors.lastname: Browning
authors.affiliation: Department of Physics and the Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA.
authors.forename: Dehong
authors.initials: D
authors.lastname: Hu
authors.affiliation: Department of Physics and the Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA.
authors.forename: Mikhail
authors.initials: M
authors.lastname: Zamkov
authors.affiliation: Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Wayne P
authors.initials: WP
authors.lastname: Hess