New approach for analyzing the vertical structure of polymer thin films based on surface-enhanced Raman scattering

We report on a new approach for measuring the chemical composition of the 20 nanometers at the top or bottom of a polymer film. This approach is based on a variation of the surface enhanced Raman scattering effect with laser illumination through a thin gold layer (∼4 nm). We show that the introduction of the thin gold layer has little or no effect on the morphology of the film that is spin coated on top of it. We demonstrate that this technique has better than 20 nanometer vertical resolution by studying bilayers of polyfluorines with varying thicknesses and by showing the existence of top and bottom wetting layers in a polymer blend of the same polymers. We also show that the top wetting layer is thinner than the bottom one. The difference in thicknesses explains how a solar cell with an electron blocking layer at the cathode works.