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Force Imaging

Force Calibration (Contact Mode AFM)

Rev. D Dimension 3100 Manual 221

discusses general approach adjustments to improve force curves obtained after engaging the

microscope.

The basic approach to obtaining a good force curve entails adjusting the Z motion of the piezo

relative to the sample (with the Z scan start and Ramp size parameters) and shifting the graph

(with the Setpoint parameter) so the pull-off point of the tip displays on the graph. In general, use

the following steps to obtain a good force curve:

1. Engage and verify the tip is tracking the surface. Then switch to Force Calibration mode.

2. Maximize the Deflection Limit parameter in the Feedback Controls panel.

3. In the Channel 1 panel select Deflection as the Data Type.

4. Maximize the Data Scale parameter.

5. Adjust the Ramp size parameter to about 1µm.

6. If the tip does not reach the sample surface (for example, see Figure 13.4a, between points 2

and 3), slowly increase the Z scan start value.

7. As the Z scan start increases, the traces on the force curve move to the right.

8. Adjust the Setpoint parameter.

Note: Adjusting the Setpoint value moves traces up and down on the graph.

Decreasing the value moves the curve up while increasing the value moves the

curve down. (Remember that the green horizontal centerline of the graph is

equal to the Setpoint if the Data Center = 0, so that changing the Setpoint

actually shifts the graph up and down.) Typically, changing the Setpoint value

to -2 volts shows the desired features of the force curve. If it does not, decrease

the Setpoint value further.

Note: Sometimes the entire ramp will occur in the contact portion of the curve (see

Figure 13.4a, between points 3 and 5). If this occurs, increase the Ramp size

and/or decrease the Z scan start.

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