SERS Enhancement and Field Confinement in Nanosensors Based on Self-Organized Gold Nanowires Produced by Ion-Beam Sputtering

Year: 2014

Authors: D’Andrea C., Fazio B., Gucciardi P.G., Giordano M.C., Martella C., Chiappe D., Toma A., Buatier de Mongeot F., Tantussi F., Vasanthakumar P., Fuso F., Allegrini M.

Autors Affiliation: CNR, IPCF, I-98156 Messina, Italy; Univ Genoa, Dipartimento Fis, I-16146 Genoa, Italy; CNISM, I-16146 Genoa, Italy; Univ Pisa, Dipartimento Fis Enrico Fermi, I-56127 Pisa, Italy; CNR, INO, Sez Pisa, I-56127 Pisa, Italy.

Abstract: Since its discovery, surface-enhanced Raman spectroscopy (SERS) has pushed researchers’ interest to develop different kinds of active substrates for high sensitivity molecular detection. Defocused ion beam sputtering (IBS) represents a viable route for the production of large scale, highly reproducible SERS-active substrates consisting of near-field coupled nanowires featuring localized surface plasmon resonances in the visible and the near-infrared. Here we investigate the field enhancement and spatial confinement in the visible and the near-infrared of arrays of optically resonant gold nanowires, using two complementary techniques: SERS and scanning near-field optical microscopy (SNOM). While SERS allows us to quantify the field enhancement factor, SNOM is used to image the localization of the enhanced electromagnetic fields. We show that in the visible (633 nm) the nanowires are SERS active only for excitation polarized parallel to the wire-to-wire nanocavities, yielding enhancement factors of 7 X 10(3). In the near-infrared (785 nm) we observe a 2-fold larger SERS enhancement (1.3 x 10(4)) for excitation parallel to the nanocavities and detect the onset of SERS amplification for excitation polarization parallel to the nanowires long axis. Polarization-sensitive SNOM in the near-infrared (830 nm) enables the correlation of the scattered intensity with the sample morphology at the local scale. We demonstrate that the field enhancement stems from the wire-to-wire nanocavity regions when the excitation field is polarized parallel to the wire-to-wire nanocavity, while we observe more complex field confinement patterns related to the partially inhomogeneous morphology of the substrate when the polarization is parallel to the nanowires long axis. Our experiments strongly suggest IBS-fabricated nanowires as novel substrates for plasmon-enhanced spectroscopies.

Journal/Review: JOURNAL OF PHYSICAL CHEMISTRY C

Volume: 118 (16)      Pages from: 8571  to: 8580

More Information: We acknowledge support by MIUR under Project PRIN 2008J858Y7. B.F., C.D’A., and P.G.G. acknowledge funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 241818 (FP7-HEALTH-F5-2009-241818-NANOANTENNA). F.B.d.M. acknowledges funding by MSE in the framework of the Operating Agreement with ENEA for Research on the Electric System and by MAE under GR Italy-Poland bilateral program. F.T., F.F., and M.A. are grateful for partial funding to NanoSci E+ program under Grant E2-PLAS (ANR-08-NSCI-007), to the project POLOPTEL funded by La Fondazione Pisa and to the exchange project between University of Pisa and University of Paris-Sud, Orsay. Fruitful discussions with Anne Debarre are gratefully acknowledged.
KeyWords: Raman-scattering; Surface-plasmon; Nanostructured Surfaces; Optical Microscope; Methylene-blue; Nanoparticles; Absorption; Arrays; Fluorescence; Excitations
DOI: 10.1021/jp5007236

ImpactFactor: 4.772
Citations: 50
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