Chemical imaging of the surface of self-assembled polystyrene-b-poly(methyl methacrylate) diblock copolymer films using apertureless near-field IR microscopy.

The nanoscale chemical composition variations of the surfaces of thin films of polystyrene- b-poly(methyl methacrylate) (PS- b-PMMA) diblock copolymers are investigated using apertureless near-field IR microscopy. The scattering of the incident infrared beam from a modulated atomic force microscopy (AFM) tip is probed using homodyne detection and demodulation at the tip oscillation frequency. An increase in the IR attenuation is observed in the PMMA-rich domains with a wavenumber dependence that is consistent with the bulk absorption spectrum. The results indicate that even though a small topography-induced artifact can be observed in the near-field images, the chemical signature of the sample is detected clearly.