Two-dimensional surface-enhanced Raman imaging of a roughened silver electrode surface with adsorbed pyridine and comparison with AFM images

Raman scattered light from pyridine adsorbed on an electrochemically roughened silver electrode surface was used to image the two-dimensional surface morphology with a spatial resolution of 1 mu m. The images showed that the spatial distribution and intensity of the surface-enhanced Raman scattered (SERS) light intensity varied to a significant extent over the electrode surface and revealed apparent surface features, specifically, ridges and domes with dimensions on the order of 10 mu m. Atomic force microscopic images also showed similar structures. In addition, the AFM images showed that smaller surface features, on the order of 1-3 mu m, were associated with brighter areas in the SERS images. However, the difference in SERS intensities for bright vs dark areas was at most a factor of similar to 6, indicating that, even in the dark areas, there was significant surface enhancement. Consistent with this result is the fact that, at still higher magnification, the AFM images in different areas of the electrode showed very similar surface structure, consisting of silver particles with diameters in the range 50-400 nm.