Imaging phase-separated domains in conducting polymer blend films with near-field scanning optical microscopy.

We present high-resolution images with near-field scanning optical microscopy to study phase separation in polymer films of poly(styrene) and poly(3-octyl-thiophene). Transmission and transmitted fluorescence near-field scanning optical microscope images were taken for direct visualization of the intermediate steps of phase separation in a regime where small domain sizes prevent investigation by conventional microscopy. The interpretation of near-field data on samples with large or varying film thickness or topography are also discussed, and a method for recognizing topographically induced artifacts in a quantitative way is suggested.