Through collaborations with the Biotechnology Division of NIST's Chemical Science and Technology Laboratory, we have chemically modified contact and tapping mode AFM probe tips with a variety of functional groups.  In particular, hydrophobic (CH₃-terminated) probes and hydrophilic (COOH-terminated) probes have been used in several AFM studies of tip-sample adhesion force and to study changes in friction and phase contrast.  An example is shown above in which a 50:50 poly(methyl methacrylate)-polystyrene (PMMA-PS) blend is imaged first in tapping mode with an unmodified tapping probe (top set of images on left) and then in contact mode with a hydrophilic probe (middle set of images on left) and a hydrophobic probe (bottom set of images on left).  The tapping phase image, which is most sensitive to mechanical property differences, shows no contrast between PMMA and PS regions.  However, the friction images taken with the chemically modified probes show significant contrast between the phase-separated regions, presumably due to differences in surface chemical properties, although topographic affects on the friction contrast are also observed.