Spatially resolved surface-enhanced Raman scattering and second harmonic generation studies of electrochemical and laser-microfabricated interfaces with a scanning laser microprobe

A scanning laser microprobe was constructed to study problems in ultrasensitive analysis, surface heterogeneity and laser microfabrication. Despite high irradiance, required because surface Raman intensity is independent of laser spotsize, spatially resolved surface enhanced Raman spectroscopy (SR-SERS) of molecular monolayers on Ag electrodes is feasible, non-destructive, and capable of detecting a few attomoles of localized material. At unfavorable excitation wavelengths, several N-heterocyclic adsorbates underwent decomposition to C(a); absence of free-molecule excited states and linear power dependence of the decomposition rate imply the excitation of a chemisorbed metal-molecule state. The inefficient reactive pathway is observed at high irradiance, but generally not in conventional SERS.;SR-SERS and spatially resolved second harmonic generation (SR-SHG) images were used to investigate enhancement heterogeneity on smooth and anodized Ag. Residual enhancement from polishing defects below the resolution of the microscope is uniform; heterogeneously distributed enhancement is only noted if large scale defects deliberately remain. For anodized electrodes, enhancement is not homogeneous, but the slight heterogeneities found are not as large as previously claimed. Enhancement heterogeneity was also produced by laser photoanodization on Ag. A unique combination of Raman and SHG imaging was used to separate electromagnetic and chemical parts of the enhancement on these surfaces: photoanodization enhancement results from small scale differences in chemisorption sites rather than differences in the size and shape of larger scale roughness features determining electromagnetic enhancement.;Electromagnetic surface enhanced second harmonic generation (SESHG) from an 1064 nm incident laser was observed for the first time from Pt. Both mechanically polished Pt and microstructured Pt prepared by laser microchemical etching in Cl...