Biomedical Engineering Reference
In-Depth Information
Fig 4.6. The effect of different feedback settings. The motion of the probe over a simple sample,
resembling a calibration/test grid (left), and the oscilloscope window showing deflection (
z
-error)
and height information (right). Note that feedback in AFM is never instantaneous, so the bottom
example still shows some imperfections.
Note that gain, speed, and set-point are all related. At low scan speeds, low gains, and low
set-point (low applied force) may be adequate, but faster speeds typically require higher
gains, and might require higher set-point.
4.2.4 Choosing scan size and zooming
If the sample is heterogeneous, and certain features must be scanned, normally it helps to
start with a large scan of the area, and then zoom to the feature of interest (see Figure 4.8).
Zooming directly into features with AFM works well for instruments with scan lineariza-
tion (see Chapter 2). With non-linearized scanners, it is best to zoom in 'gradually', by
zooming to no than less than 50% of the current image size at a time. Thus, several zooms
may be required to find the region of interest.
