Metal‐catalyzed oxidation of poly(α‐methylstyrene) during surface‐enhanced Raman scattering

Abstract

Abstract Surface‐enhanced Raman scattering (SERS) was used to characterize thin films of poly(α‐methylstyrene) (PMS) spin‐coated onto silver island films supported by glass substrates. At laser powers of a few tens of milliwatts, SERS spectra of thin films of PMS (about 100 Å) were weak, and only the bands near 1010 and 1040 cm −1 were observed. At laser powers of about 100 mW, additional bands characteristic of PMS were observed near 720 and 1610 cm −1 . However, oxidative degradation of the PMS films to form graphite‐like substances was also observed at the higher laser powers. When the thickness of the PMS films was increased to several hundred angstroms, degradation of the films was inhibited, but the intensity of the Raman scattering remained constant, indicating that the observed SERS was an interfacial rather than bulk effect. Degradation during SERS experiments was also inhibited by overcoating PMS films with much thicker films of poly(4‐styrene sulfonate) (PSS). Scattering from the PSS overlayers was not observed as long as the thickness of the PMS films was greater than several tens of angstroms, again showing that the SERS was an interfacial effect. Oxidative degradation of the PMS films was also inhibited by adding a few percent of the antioxidant 2,6‐di‐ tert ‐butyl‐4‐methylphenol to the polymer. Bands related to sulfite contaminants adsorbed onto the silver island films were observed near 640 and 940 cm −1 . These bands disappeared when PSS, but not PMS, was spin‐coated onto the SERS substrates, indicating a strong interaction between PSS and silver.