Biomedical Engineering Reference
In-Depth Information
Fig. 2.4. Schematic of feedback control; when the force sensor senses a change in sample height, the
piezoelectric moves to maintain the same tip-sample force.
tip-sample distance fixed is assumed to be equal to the sample topography. In this way, by
monitoring the voltage applied to the z piezo, a map of the surface shape (a height image )
is measured.
There are several engineering challenges that must be met to design and construct a
successful atomic force microscope. They are:
• A very sharp probe must be constructed so that high-resolution images are measured.
• To get the probe within the scanning range of the surface, a macroscopic translation
mechanism must be constructed.
• The force transducer must have a force resolution of 1 nN or less so that the probe is
not broken while scanning.
• A feedback controller that permits rapid control so that the probe can follow the
topography on the surface must be created.
•An X-Y - Z piezoelectric scanner that has linear and calibrated motion must be used.
• A structure that is very rigid must be constructed so that the probe does not vibrate
relative to the surface.
Fig. 2.5. Block diagram of AFM operation.
 
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