Biomedical Engineering Reference
In-Depth Information
Fig. 6.13. Illustration and example of errors in
Z
angle measurement by AFMcaused by crosstalk. Top:
illustration of the effect. The sample has a series of repeating triangles at its surface. A line profile of the
sample shows that the triangles do not appear symmetric. Bottom: real AFM image of a sample having a
triangle pattern at its surface, and a line profile extracted from the AFM image. Although the angles of
the two facets are in reality equal, the AFM image suggests that this is not so.
are unreliable. This error can best be measured with a sample that has repeating triangle
structures. An example of this is shown in Figure 6.13.
The user cannot control the appearance of this artefact. It occurs with non-linearized
tube scanner-based AFMs, and independent
X-Y
and
Z
scanners are required for the
measurement of correct
Z
angles.
6.3
Image processing artefacts
Some image processing is usually necessary before viewing or analysing any AFM image.
As described in Chapter 5, there are a large number of processing operations that can be
applied to AFM images. The correct procedures were described in Chapter 5, so here only
examples of the artefacts that might be introduced are shown.
6.3.1 Levelling artefacts
Levelling changes the entire AFM image, so the resulting image is different from the raw
data. However, it is very often a necessary procedure before useful information can be
extracted from an image. Commonly, levelling artefacts are introduced by polynomial
fitting routines; Figure 6.14 shows an example of this.
This error is easily avoided by excluding parts of the image from the fit. This was
described in Section 5.1.1. Despite the ease with which this artefact is avoided, it is
commonly seen in published AFM images.
6.3.2 Filtering artefacts
Image filtering, by definition, alters the data in the image and therefore always introduces
some sort of artefact. When presenting AFM data, it is important to specify what filters, if
