AbstractSurface‐enhanced Raman scattering (SERS) has been observed from thin films of polystyrene (PS), diglycidyl ether of bisphenol‐A (DGEBA), and poly(4‐vinyl pyridine) (PVP) deposited on silver island films Degradation of the polymers occurred rapidly during laser irradiation and was accompanied by the appearance of strong bands near 1375 and 1575 cm‐1. These bands were attributed to the formation of graphite‐like species by the silver‐catalyzed thermal oxidation of the polymers induced by localized laser heating of the substrate. When the thin films of PS, DGEBA, or PVP were overcoated with much thicker films of a second polymer such as polystyrene sulfonate (PSS), the degradation was greatly reduced, and excellent SERS spectra of the PS, DGEBA, and PVP films were obtained. Overlayers reduced degradation within the first films deposited on silver island films by restricting the availability of oxygen at the interface to its solubility in the overlayer polymer or by altering the adsorption of oxygen onto the substrate. SERS was observed for the PS, DGEBA, and PVP films and the PSS overlayers when the films were deposited from relatively dilute solutions. When the PS, DGEBA, and PVP films were deposited from more concentrated solutions, SERS was not observed from the PSS overlayers. It was suggested that most of the SERS was due to a short‐range, charge‐transfer mechanism associated with sites of atomic scale roughness and that SERS was observed from the overlayer when the first film failed to occupy all of the sites.

AbstractSurface‐enhanced Raman scattering (SERS) from p‐aminobenzoic acid (PABA) adsorbed on silver island films was investigated. PABA reacted very quickly to form p,p′‐azodibenzoate when exposed to atmospheric moisture and laser light. This was evidenced by the appearance of a strong band near 1460 cm−1 and a strong doublet near 1150 cm−1 that were characteristic of the azodibenzoate. Exposure to a drier environment such as in a desiccator or a vacuum inhibited the reaction. It was concluded that the reaction of PABA to form the azodibenzoate involved two steps, the first being the hydrolysis of the amine and the second dimerization during exposure to laser light.

Surface-enhanced Raman scattering (SERS) by films of polystyrene adsorbed onto silver island films was investigated. Films that were only a few tens of angstroms in thickness degraded rapidly during laser irradiation to form graphite-like species at the silver surface. However, no degradation was observed while Raman spectra of the solid polymer were obtained, indicating that the graphitization was probably induced by laser heating of the substrate and catalyzed by silver. For thin films of polystyrene, the rate of graphitization was high and was proportional to laser power. However, the degradation reaction was inhibited for thick films or for thin films overcoated with thick films of a second polymer. The Raman spectra were similar for all films thicker than approximately a hundred angstroms, even those overcoated with a thick film of a second polymer having a large Raman scattering cross section, indicating that most of the observed scattering originated from polymer molecules within a few tens of angstroms of the silver surface. It was concluded that SERS can be used to probe the molecular structure of polymer/metal interfaces without interference by scattering from the bulk of the polymer.

The surface-enhanced Raman scattering (SERS) from thin films formed by p-nitrobenzoic acid (PNBA) adsorbed onto silver island films has been investigated. SERS spectra obtained using low laser powers were very similar to the normal Raman spectra of the sodium salt of PNBA and were characterized by strong bands near 1600 and 1355 cm−1 and by weaker bands near 1395, 1115, and 875 cm−1. The band near 1395 cm−1 was assigned to the symmetric stretching mode of carboxylate groups, indicating that PNBA was adsorbed as a metal salt. When PNBA films were irradiated at high laser powers, a rapid reaction occurred. The bands near 1355 and 1115 cm−1 gradually decreased in intensity and a strong band near 1460 cm−1 and a strong doublet near 1150 cm−1 gradually appeared. The band near 1460 cm−1 and the doublet near 1150 cm−1 were attributed to azodibenzoate formed by the reductive coupling of PNBA molecules at the silver surface during laser irradiation. When adsorbed PNBA films were irradiated at low laser powers, the reaction still occurred but at a much lower rate. Reduction of PNBA was probably thermally induced but a photochemical mechanism may also be possible.