Chapter 2
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2.2.3 Integrating LL-Force Sensors and Scanners |
The initial AFM designs scanned the sample and kept the probe stationary.
This simpler type of design was optimal for only limited types of samples.
It became advantageous to design AFM scanners where the X-Y-Z scanner
is integrated with the LL-AFM force sensor. |
The initial AFM designs scanned the sample and kept the probe stationary. This simpler type of design was optimal for only limited types of samples. It became advantageous to design AFM scanners where the X-Y-Z scanner is integrated with the LL-AFM force sensor. The easiest approach to integrating an X-Y-Z scanner would be to mount the LL sensor at the end of the scanner. This is not feasible because the Z piezo is not responsive enough to move the entire light lever scanner up and down as the probe is scanned across the surface. Such an AFM would be too slow to be practical. Two methods are employed for creating a combined LL-AFM scanner with an X-Y-Z scanner. |
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FIGURE 2-19 Two designs for tip scanning light lever AFM scanners. Left: The laser is scanned with the cantilever. Right: The laser is fixed and the cantilever is scanned, a lens keeps the laser light focused on the cantilever. |
In the first, illustrated schematically in Figure 2-19, the laser and photo-detector are scanned in the X-Y axis, and the probe is mounted at the end of the Z ceramic. In this design the Z ceramic is part of the light lever optics. That is, as the probe is moved up and down in the Z direction the light path changes. It can be shown geometrically that the Z motion of the cantilever has a minimal effect on the operation of the AFM LL-AFM sensor. |
Also illustrated in Figure 2-19, is the other approach commonly used. The laser is held fixed and a lens is used to focus the laser light onto the cantilever. As the lens moves back and forth in the X-Y plane, the laser light stays focused on the cantilever. The photo-detector is then mounted on the X-Y translator. |
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