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Force Imaging

Force Calibration (Contact Mode AFM)

Rev. D Dimension 3100 Manual 223

Adjust Photodiode

In an analogous manner, you can use the photodiode positioner as a coarse adjustment for Setpoint

voltage. Changing the laser beam position on the photodiode by rotating the photodiode adjustment

knobs shifts the force curve on the graph. Rotating the top photodiode adjustment knob clockwise

shifts the curve up, just as decreasing the Setpoint parameter shifts the curve up. Conversely,

rotating the top photodiode adjustment knob clockwise moves the curve down.

13.4.3 Advanced Techniques

Sensitivity Determination

The Deﬂection Sensitivity allows conversion from the raw photodiode signal (in Volts) to

deﬂection of the cantilever (in nm), and is normally set from the Force Calibration mode. The

sensitivity must be calibrated before accurate deﬂection data can be obtained. Sensitivity is equal to

the inverse of the slope of the force curve while the cantilever is in contact with a hard sample

surface. Complete the following steps to calculate the sensitivity:

1. Obtain a good force curve on the display monitor using a hard sample so that the sample does

not deform.

2. Position the cursor on one end of the contact portion of the curve.

3. Click on the left mouse button to fix the line segment.

4. Drag the mouse to position the “rubber band line” parallel to the contact portion of the force

curve (see Figure 13.4d).

Figure 13.4d Set the Sensitivity Parameter

5. The second click on the mouse causes the system to calculate the slope of the line segment

and enter the -1/slope as the Sensitivity in the panel.

6. A click of the right mouse button will remove the line segment from the screen.

Click and drag line parallel to plot

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Dell 3100 Spezifikationen Seite 243