Scattering-type near-field infrared microscopy of selforganized nanodomains of diblock copolymers

The expansion of scattering-type scanning near-field optical microscopy ({\em s}-SNOM) into the infrared spectral region provides the ability to achieve all-optical resolution down to the several nanometer range in combination with the chemical sensitivity of infrared spectroscopy. Here, we have performed a nanometer scale surface analysis and identification of domains formed by phase separation of the diblock copolymers polystyrene-{\em b}-polyvinylpyridine (PS-b-P2VP) and polystyrene-{\em b}-polyethyleneoxide (PS-b-PEO). This has been achieved by means of non-interferometric IR-scattering detection based on epi-illumination of sharp Au-coated cantilever tips in a noncontact atomic force microscopy configuration. Contrast is obtained probing characteristic differences in the C--H stretch vibrational resonances between the different polymer constituents and a spatial resolution down to 10 nm has been made possible. The mechanism of the near-field tip-sample coupling by vibrational resonances responsible for the imaging contrast has been deduced and can be modelled based on the dielectric functions of the polymer compounds measured by spectroscopic ellipsometry.