title: Surface-enhanced Raman scattering of 4-aminobenzenethiol in Ag sol: relative intensity of a1- and b2-type bands invariant against aggregation of Ag nanoparticles.
abstract: 4-Aminobenzenthiol (4-ABT) is an unusual molecule, showing variable surface-enhanced Raman scattering (SERS) spectra depending upon measurement conditions. In an effort to reduce ambiguity and add clarity, we have thus conducted an ultraviolet-visible (UV-vis) extinction measurement, along with Raman scattering measurement, after adding 4-ABT into aqueous Ag sol. Upon the addition of 4-ABT, the surface plasmon absorption band of Ag at 410 nm gradually diminished and, concomitantly, a weak and broad band developed at longer wavelengths, obviously because of the aggregation of Ag nanoparticles. At the same time, the Raman scattering peaks of 4-ABT varied in intensity as the Ag particles proceeded to form aggregates. A close examination revealed that the peak intensity of the ring 7a band of 4-ABT, a typical a(1) vibrational mode, could be correlated with the UV-vis extinction of the Ag sol measured at the excitation laser wavelength. In a separate Raman measurement conducted using sedimented Ag colloidal particles, 4-ABT was found not to be subjected to any surface-induced photoreaction, implying that all of the observable Raman peaks were, in fact, solely due to 4-ABT on Ag. The intensities of the b(2)-type bands, such as the ring 3, 9b, and 19b modes of 4-ABT, were then analyzed and found to be invariant with respect to the 7a band, irrespective of the extent of Ag aggregation as far as at a fixed excitation wavelength. The intensity ratio of the b(2)-type/7a bands would then reflect the extent of the chemical enhancement that was involved in the SERS of 4-ABT in aggregated Ag sol.
authors.affiliation: Department of Chemistry, Seoul National University, Seoul 151-742, Korea. kwankim@snu.ac.kr
authors.forename: Kwan
authors.initials: K
authors.lastname: Kim
authors.forename: Jae Keun
authors.initials: JK
authors.lastname: Yoon
authors.forename: Hyang Bong
authors.initials: HB
authors.lastname: Lee
authors.forename: Dongha
authors.initials: D
authors.lastname: Shin
authors.forename: Kuan Soo
authors.initials: KS
authors.lastname: Shin
mesh_terms: D001557:Benzenesulfonates / Q000737:chemistry*; D019281:Dimerization; D053768:Metal Nanoparticles / Q000737:chemistry*; D012834:Silver / Q000737:chemistry*; D013059:Spectrum Analysis, Raman; D013425:Sulfanilic Acids / Q000737:chemistry*
chemical_list: D001557:Benzenesulfonates; D013425:Sulfanilic Acids; D012834:Silver; C100016:4-sulfanilic acid