| Abstract
| - The interfacial structures of biphenyl (BP), benzoic acid (BA), and 4-biphenylcarboxylic acid (BPCA) ona Au colloid monolayer surface were investigated using surface-enhanced Raman scattering (SERS). Theabsence of the C−H stretching vibrational mode in the SERS spectrum of BP indicated that the twobenzene rings of BP were coplanar on the Au colloid surface, while their twisted structure was suggestedin the bulk state. The downward frequency shift of the carboxylate stretching vibrational mode of BAimplied the direct chemical adsorption of the carboxylate group onto the Au surface with a flat orientation.In BPCA, an absence of the C−H stretching vibrational mode and the red shift of the carboxylate stretchingvibrational mode were observed. This fact strongly indicated that both the two benzene rings and thecarboxylate group were adsorbed on the Au surface with flat orientation via their π-systems.
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