Surface-enhanced Raman scattering of 4-aminobenzenethiol on silver: confirmation of the origin of b2-type bands

초록

In order to resolve the dispute on the origin of the b2-type bands in the surface-enhanced Raman scattering (SERS) of 4-aminobenzenethiol (4-ABT), we have measured its SERS spectra under a variety of conditions, including variable temperature and rotation, electrochemistry, and pH, as well as in the presence of a reducing agent. For comparison, the SERS spectra of 4-nitrobenzenethiol (4-NBT) and methyl orange (MO), a prototype azo compound, were also measured. First, we found that 4-ABT on Ag is not subjected to photoreaction, although 4-NBT is highly photoreactive on a silver surface. In the electrochemical environment, b2-type bands of 4-ABT lost their intensity at very negative potentials, but the intensity recovered immediately upon raising the potential. In addition, b2-type bands were observed under rotation even after lowering the potential. The disappearance and reappearance of the b2-type bands could also be observed by bringing the sample of 4-ABT on Ag into contact consecutively with a borohydride solution and water. This is because the surface potential of Ag is lowered by contact with a borohydride solution. Besides, we found that not only the normal Raman but also the SERS spectral features of 4-ABT are hardly affected by pH variation, while the spectral features of MO are greatly affected, especially in the region of the N?N stretching vibration, suggesting that the possibility of a photoconversion of 4-ABT to an azo compound is low. Altogether, the b2-type bands were attributed to 4-ABT, appearing in conjunction with the chemical enhancement mechanism in SERS. Copyright (C) 2011 John Wiley & Sons, Ltd.

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