Biomedical Engineering Reference
In-Depth Information
Fig. 5.8. Examples of 3-D renderings of height information. Left: DVD bits, right: human blood
cells. Three-dimensional rendering greatly helps the viewer to visualize the shape of the sample, as
well as to see both large and small features simultaneously.
special glasses to differentiate the left eyes and right eyes views, and can help to visualize
the shape of the sample topography.
AFM images are highly suitable for further analysis, and it is rare that only displaying the
images acquired is sufficient to fully characterize the sample under study. Thus, very
commonly further analysis is carried out in order to obtain quantitative information about
the sample. Of course, the quantitative measurements derived from AFM images are only
as good as the quality of the measurements. Thus, for the best data analysis the image must
be acquired and processed properly. For example, if the images have errors due to poorly
chosen acquisition parameters or dull probes, or have been inadequately processed the
analysis will reflect these problems.
5.3.1 Line profiles
One of the most common analysis techniques is the extraction and measurement of
line profiles. Because AFM images are difficult to measure dimensions directly from,
line profiles are usually extracted in order to measure dimensions from the AFM images.
The AFM analysis software allows the user to arbitrarily define lines to be extracted, and
these can be horizontal, vertical or at any angle. The software then constructs a new plot,
with distance along the chosen line on the
x
axis, and sample height on the
y
axis. In the
new plot, the user can easily measure feature heights, widths, and angles. An example
showing an image with an extracted line profile, and measurements of these parameters, is
shown in Figure 5.9.
Figure 5.9 illustrates an important application of measurement of line profiles. Micro-
fabricated devices such as these DVD master bits have very specific tolerances in their
dimensions which directly affect their performance. Line profiles such as this can give
very accurate measurements in such samples. It is important to be aware of the sources of
error in such measurements. In an example such as this, the spacing between the bits
