Investigation of surface-enhanced Raman scattering from platinum electrodes using a confocal Raman microscope: dependence of surface roughening pretreatment
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In order to establish an appropriate surface roughening procedure for obtaining high-quality surface Raman spectra from Pt electrodes, various roughening conditions for the SERS from the adsorbed pyridine, thiocynate and hydrogen are assessed in terms of the corresponding surface Raman intensities, enhancement factors and surface homogeneity. The repetitive square-wave oxidation reduction cycle (SWORC) triangular-wave ORC (TWORC) and platinization have been performed in the present study. The enhancement factor (G) is calculated based on the confocal feature of a confocal microprobe Raman system, showing one to two orders of amplification of Raman signal for adsorbed pyridine on roughened Pt surfaces. The involvement of charge transfer (CT) enhancement is inferred from the SERS intensity-potential profiles that are dependent on excitation lines. In general, the Pt surfaces with different roughness factors (R) can be divided into three categories: (1) the mildly roughened surface with R of 20-30 seems more adequate for the study of SERS mechnism including calculation of G. (2) the moderately roughened surface with R ranging from 20 to 100, providing homogeneous morphologies: is suitable for investigating surface adsorption and reactions; (3) the highly roughened surface with R ranging From 100 to 300, with non-uniform morphologies, could only be used for investigating species having small Raman cross-sections such as hydrogen adsorption. (C) 1998 Elsevier Science B.V. All rights reserved.