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Fluid Imaging

Operating Principles

172 Dimension 3100 Manual Rev. D

TappingMode

Usually the best images are obtained at setpoints 5-10 percent less than the cantilever RMS

amplitude before engaging. The setpoint may be optimized in one of two ways:

• Use the Force Calibration Command: The Force Calibration command plots the

cantilever amplitude versus the scanner position. A typical Force Calibration is shown in

Figure 10.5c. The curve should show a mostly ﬂat region where the cantilever has not

yet reached the surface and a sloped region where the amplitude is being reduced by the

tapping interaction. Set up the Force Calibration as described for TappingMode in air

(see Section 13.5). (Experienced users may use the Force Step command instead). To

protect the tip and sample, take care that the cantilever amplitude is never reduced to

zero. Adjust the setpoint until the green “setpoint line” on the graph is just barely below

the ﬂat region of the Force Calibration curve. This is the setpoint that applies the lowest

force to the sample.

Note: The slope of the Force Calibration curve shows the sensitivity of the ﬂuid

TappingMode measurement. In general higher sensitivities will give better

image quality. If the sensitivity is very poor, consider changing to a different

drive frequency or check the mounting of the sample and ﬂuid cell.

• Optimize the Image Quality: The Setpoint can also be adjusted by simply monitoring

the image quality.

• Select a Scan size of 500nm.

• Increase the Setpoint in small increments until the cantilever pulls off the surface

and the Z center voltage is at -220V.

• Reduce the Setpoint in small increments until an image appears. Continue reducing

the Setpoint until the image is optimized. Usually the best images are obtained at

setpoints just below where an image appears.

When operating in TappingMode, it may be necessary to check the cantilever tuning after the

system is engaged. To check the cantilever tuning:

1. Select View > Sweep > Cantilever Tune.

2. Set the Tip Offset to 200nm and click OK.

3. Once in the cantilever tuning window, adjust drive frequency and drive amplitude if

necessary.

10.5.19 Clean Cell and Protective Skirt

When you are ﬁnished scanning, remove and clean the ﬂuid probe holder and protective skirt,

following the procedure described in Section 10.5.1. In the Feedback Panel, set Z Modulation to

Disabled.

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