Nanoscale probing of a polymer-blend thin film with tip-enhanced Raman spectroscopy.

Fundamental advances have been made in the spatially resolved chemical analysis of polymer thin films. Tip-enhanced Raman spectroscopy (TERS) is used to investigate the surface composition of a mixed polyisoprene (PI) and polystyrene (PS) thin film. High-quality TER spectra are collected from these nonresonant Raman-active polymers. A wealth of structural information is obtained, some of which cannot be acquired with conventional analytical techniques. PI and PS are identified at the surface and subsurface, respectively. Differences in the band intensities suggest strongly that the polymer layers are not uniformly thick, and that nanopores are present under the film surface. The continuous PS subsurface layer and subsurface nanopores have hitherto not been identified. These data are obtained with nanometer spatial resolution. Confocal far-field Raman spectroscopy and X-ray photoelectron spectroscopy are employed to corroborate some of the results. With routine production of highly enhancing TERS tips expected in the near future, it is predicted that TERS will be of great use for the rigorous chemical analysis of polymer and other composite systems with nanometer spatial resolution.