Biomedical Engineering Reference
In-Depth Information
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Fig. 3.19. Examples of phase contrast in IC-AFM on different samples. Top: a triblock copolymer
topography (left) barely shows height differences for the different phases. The phase image (right)
shows clear contrast. Bottom: Langmuir-Blodgett film on mica, the high topography region (the
monolayer) has a higher phase contrast than the mica in the phase image. This image shows how the
edges of these phases also show different contrast in the phase image, due to changes in tip-sample
contact area.
popularity of IC-AFM, and the fact that obtaining the data is very simple and does not
require post-processing of the data.
3.2.3.3 Other dynamic modes
A number of less commonly used oscillating modes have been reported [198, 199], these
are typically variations on IC-AFM, designed to make simultaneous acquisition of sample
properties and topography simpler or more quantitative. An example of this is jumping
mode AFM [198, 200-204]. This is a variant of IC-AFM, the difference being that in
jumping mode, the movement along the fast scan axis is discrete, rather than continuous,
and the electronics are set up to record the cantilever deflection at specific points along the
force-distance curve during each oscillation. The advantage of such a technique is that if,
for instance, the points recorded are equivalent to points a and b in Figure 3.2, the
tip-sample adhesion may be obtained, or slope data (see Figure 3.15) could be recorded
to qualitative sample stiffness. The advantage of this particular mode is that the relatively
high-speed scanning of IC-AFM can be combined with the acquisition of such data. This is
also the aim of pulsed-force mode [199, 205-207], which operates in a very similar way to
jumping mode, although fast scan axis movement is continuous, like normal IC-AFM. As
