Biomedical Engineering Reference
In-Depth Information
Fig. 3.10. Intermittent-contact operating regime. In this mode, the AFM probe's oscillation is large
enough to move from the repulsive regime, through the attractive regime, and completely out of
contact in each cycle.
(ii) Due to the movement of the tip perpendicular to the surface as it scans, lateral
forces are (almost) eliminated.
(iii) The tip passes through the contamination layer (see Figure 3.11).
(iv) Tip-sample contact also allows some sensing of sample properties.
(v) The feedback system requires the collection of adequate data to characterize the
cantilever oscillation in terms of its amplitude.
Points (ii) and (iii) above explain the popularity of IC-AFM. The lateral forces which can
cause great problems in contact-mode AFM do not affect IC-AFM. On the other hand, the
fundamental instability of non-contact AFM in air (due to operation in the attractive
regime, and the presence of the capillary layer) is overcome, making IC-AFM somewhat
simpler to achieve. In IC-AFM, the restoring force of the cantilever withdraws the tip from
the contamination layer in each cycle, thus reducing the effect of capillary forces on the
image.
Fig. 3.11. Intermittent-contact-mode imaging conditions in air. The probe passes through the
contamination layer to touch the substrate surface, and out again.
