Force ImagingObtaining a Good Force Curve continued.... Figure 13.5d Adjusted Force Curve for 90 µm Scanner 13.5.2 Helpful Suggestions To minimize or calculate the contact force between
Trang 1Force Imaging
Obtaining a Good Force Curve continued
Figure 13.5d Adjusted Force Curve for 90 µm Scanner
13.5.2 Helpful Suggestions
To minimize or calculate the contact force between the tip and sample, it is important to obtain a good force curve; however, there will be situations where you will not obtain a good force curve no matter how much you adjust
the Ramp size, Z scan start and Setpoint The following sections discuss a few such situations Suggestions on working in Force Calibration mode are
included
False Engagement
Figure 13.5e illustrates a force curve resulting from a falsely engaged tip The photodiode receives light reflected off the sample, causing an increase in the deflection signal until the signal equals the setpoint and the system engages (even though the tip is not on the surface)
Interference in the reflected light causes the hump-shaped waveform
Although you can use the Tip Down button to move the tip down to the
surface, the easiest way to correct a false engagement is to withdraw the tip, adjust the photodetector positioner to make the top/bottom
differential voltage more negative, then re-engage the tip This has the effect of pushing the cantilever farther up before the Setpoint is reached
Tip
Deflection
0.48 V/div
Z Position - 10.00 V/div Setpoint
Retracting Extending
Trang 2Force Imaging
Obtaining a Good Force Curve continued
Figure 13.5d Adjusted Force Curve for 90 µm Scanner
13.5.2 Helpful Suggestions
To minimize or calculate the contact force between the tip and sample, it is important to obtain a good force curve; however, there will be situations where you will not obtain a good force curve no matter how much you adjust
the Ramp size, Z scan start and Setpoint The following sections discuss a few such situations Suggestions on working in Force Calibration mode are
included
False Engagement
Figure 13.5e illustrates a force curve resulting from a falsely engaged tip The photodiode receives light reflected off the sample, causing an increase in the deflection signal until the signal equals the setpoint and the system engages (even though the tip is not on the surface)
Interference in the reflected light causes the hump-shaped waveform
Although you can use the Tip Down button to move the tip down to the
surface, the easiest way to correct a false engagement is to withdraw the tip, adjust the photodetector positioner to make the top/bottom
differential voltage more negative, then re-engage the tip This has the effect of pushing the cantilever farther up before the Setpoint is reached
Tip
Deflection
0.48 V/div
Z Position - 10.00 V/div Setpoint
Retracting Extending