TAPPING SCANNING FORCE MICROSCOPY IN AIR-THEORY AND EXPERIMENT

Ultrathin layers of micelles of a diblock copolymer with a polystyrene corona and a poly(2-vinylpyridine) core have been studied by tapping scanning force microscopy in air, probing the surface with varying for ces depending on the setpoint of the probe and the tapping frequency. The compliance of the core of the micelles was varied by neutralizatio n of the pyridine groups with HAuCl4 and incorporation of small partic les. The apparent deformation of the globular micelles was compared wi th a simple model describing the probe as a forced oscillator which ch anges its effective spring constant depending on the direct contact wi th the surface. Consistent with the experiment, the model shows that t he deformation and the shift in phase are minimized by tapping on the low-frequency side of the noncontact cantilever resonance.