Biomedical Engineering Reference
In-Depth Information
Appendix A. In this chapter, images of tip-check samples that were acquired with faulty
probes are shown, along with images measured with a new probe, to illustrate the effect
that probe damage has on the images obtained.
6.1.1 Blunt probes
Typically, blunt probes will lead to images with features larger than expected, with a
flattened profile, due to the effect shown below. Note that holes in a flat surface will show
the opposite effect, appearing smaller with blunt probes than with sharp ones (see the
lower part of Figure 6.1).
The dilation due to the probe shape as shown in Figure 6.1 is a normal feature of AFM
imaging. For example, when measuring globular features with a known diameter of 2 nm
it would be normal to find the feature in the AFM image has 2 nm height but 10-20 nm
width [279, 375, 376]. However, when it occurs to a large extent it is a problem, because it
may significantly alter the apparent size of the features, and can really change their
appearance. An example is shown in Figure 6.2. If this effect is noticed, the user should
change the probe. If the feature cannot be imaged correctly even with newer probes, then
another type of probe (e.g. super-sharp probes or high-aspect-ratio probes) may be
required [377]. However, some extremely high-aspect-ratio features can be extremely
challenging to image by AFM, no matter which probe is chosen.
The fine details of the BOPP sample when imaged with a sharp probe are seen in the left
image in Figure 6.2. When imaged with a blunt, worn probe, as shown in the right image,
they disappear, and the sample becomes almost unrecognizable. An example of the effect
of pits in a sample becoming smaller with a dull probe is shown in Figure 6.3.
Fig. 6.1. Illustration of probe-based dilation. Convex features such as particles tend to appear wider
with blunter probes, although feature height may be accurate. Concave features such as pits tend to
appear smaller (both less wide and less deep) with blunter probes.
