Chapter 3
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| across the surface. The scanning can be made in two dimensions; the probe
is scanned in a line scan, back and forth across the surface. Alternatively, a
scan can be initiated. The motion of the probe as well as the Z error signal is
displayed in a two dimensional oscilloscope window (see Figure 3-4.) |
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| FIGURE 3-4 Optimizing the PID parameters is done by assuring that the probe is tracking surface features. An oscilloscope window is often helpful for this. |
The scan parameters such as the set-point voltage, and the PID parameters are adjusted as the line scan is being made. The goal in adjusting the scan parameters is to have the probe track the surface. The probe is tracking the surface when the Z error signal image has a minimal signal. Establishing
the optimal conditions requires practice and some intuition. |
When first learning to operate an AFM, it is helpful to operate with a test sample and adjust the PID settings to see the effect on the Z voltage and the Z error signal, as shown in Figure 3-5. |
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FIGURE 3-5 Top: If the PID parameters are all zero, the cantilever will bend as it moves across the surface features. Bottom: If the PID parameters are optimized, the cantilever deflection remains constant while scanning. |
3.5. Scan Image / Zoom |
After the scan parameters are optimized, a scan is initiated. The range of the first scan depends on the specific sample being examined. A scan that |
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