Raman spectroscopy and Raman imaging were used to examine several types of carbon electrode materials, including glassy carbon (GC) and highly ordered pyrolytic graphite (HOPG). Variations in the intensity ratio of the D and E 2g Raman bands across the carbon surface indicated varying carbon microstructure. The D/E 2g ratio for polished GC and pyrolytic graphite edge (PG) was relatively constant, while that of basal HOPG and PG varied significantly due to defects. The spatial heterogeneity of Rhodamine 6G Raman intensity following physisorption to carbon surfaces indicated that adsorption occurs at disordered regions, particularly defects on HOPG. This observation provides visual confirmation of previously reported correlations of defect area and physisorption. Chemisorption of dinitrophenylhydrazine was observed only at edge plane regions, confirming the localization of surface carbonyl groups on graphitic edge plane. Finally, chemisorption of nitroazobenzene radical formed from a diazonium precursor occurred at both basal and edge regions, but more rapidly at edge sites. The higher concentrations observed at edges are attributable either to more rapid reduction of the diazonium precursor or to more rapid attack of the radical, compared to basal plane. The results represent the first spatially resolved Raman examination of physi-and chemisorption at the monolayer level on carbon surfaces.

Published Raman spectra are rarely corrected for variations in spectrometer sensitivity across the Raman spectrum, which leads to often severe distortion of relative peak intensities that impede calibration transfer and library searching. A method was developed that uses the known luminescence of standards which fluoresce in response to laser irradiation. Since the standards are observed with the same sampling geometry as the Raman sample of interest, their spectra are subject to the same instrumental response function. After one-time calibration of the standards' fluorescence output against a known tungsten source, the unknown Raman spectrum may be corrected for instrumental response by a simple formula. In practice, the user need only run the standard under the same conditions as the Raman sample, then apply a short GRAMS algorithm. The approach is demonstrated for coumarin 540a and Kopp 2412 glass standards, with 514.5- and 785-nm laser light, respectively. Once the corrected spectrum is in hand, the absolute Raman cross section of a given Raman feature may be determined by comparison to known scatterers such as benzene.

No abstract