Phase Contrast Imaging

In tapping AFM, the phase of the cantilever is often a good probe of composite systems. Because of the high spatial resolution of the AFM, inhomogeneity can be probed at a very small length scale.

This AFM image shows a rare-earth complex dispersed on V4 mica. The complex had evaded crystallization so the hope was to directly image the complex itself on the very smooth mica substrate. This had been reported previously for these complexes evaporated onto smooth substrates in vacuuo. What was observed were chains of aggregated material. They did not appear to be small crystal habits which was not surprising as XRD data did not suggest crystallization of the complex.

To understand the nature of these aggregated structures, higher resolution images of the individual globules were examined using phase contrast AFM in tapping mode. Even below a length scale of 1 μm, these aggregated globules demonstrated considerable internal structure as evidenced by phase contrast AFM. Phase contrast AFM probes local changes in the phase of the tapping probe due to local differences in the impulse experienced by the tip due to variations in density, elasticity, etc. The phase contrast AFM showed uncorrelated domains at a length scale of a few 10's nm. Thanks to Dr. Michael Shatruk of FSU Department of Chemistry.