Authors: Liang, Haihe¹; Tian, Hong¹; McCreery, Richard L.²

Source: Applied Spectroscopy, Volume 61, Issue 6, Pages 110A-122A and 571-669 (June 2007) , pp. 613-620(8)

Publisher: Society for Applied Spectroscopy

Abstract:

Raman and ultraviolet-visible (UV-Vis) absorption spectra were obtained for nitroazobenzene (NAB) chemisorbed on smooth and rough silver, and they were compared to published spectra for NAB on sp² hybridized pyrolyzed photoresist film (PPF) surfaces. High signal-to-noise ratio Raman spectra were obtained for 4.5 nm thick NAB films on PPF and smooth Ag due to significant enhancement of the NAB scattering relative to that observed in solution. The UV-Vis spectra of chemisorbed NAB exhibited a significant shift toward longer wavelength, thus bringing the NAB absorption closer to the 514.5 nm laser wavelength. The red shift was larger for PPF than for smooth Ag, consistent with the ∼5× stronger Raman signal obtained on PPF. Deposition of Ag onto quartz without a chromium adhesion layer produced a rough Ag surface that enhanced the Raman spectrum of chemisorbed NAB by a factor of ∼1000, as expected for roughened Ag due to electromagnetic field enhancement. The strong Raman signal permitted observation of NAB at low coverage and revealed changes in the NAB spectrum as the film progressed from submonolayer to multilayer thicknesses. Finally, deposition of Ag onto PPF/NAB samples through a metal grid produced Ag squares on top of the NAB, which enhanced the Raman scattering of the NAB layer by a factor of ∼100. Deposition of a final conducting film on the Ag squares should permit in situ observation of a wide range of molecules in operating molecular electronic junctions.

Keywords: RAMAN; SURFACE-ENHANCED RAMAN SCATTERING; SERS; SURFACE; MOLECULAR ELECTRONICS; CHEMISORPTION

Document Type: Research article

DOI: http://dx.doi.org/10.1366/000370207781269765

Affiliations: 1: Department of Chemistry, The Ohio State University, 100 W 18th Avenue, Columbus, Ohio 43210 2: Department of Chemistry, National Institute for Nanotechnology, University of Alberta, Canada, T6G 2G2

Publication date: 2007-06-01

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