Dimension TM 3100 Manual Version 4.43B phần 7 ppsx

Force Imaging 13-22 Dimension 3100 Manual Rev. B 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 Set p oint Retracting Extending Force Imaging 13-22 Dimension 3100 Manual Rev. B 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 Set p oint Retracting Extending . the Setpoint is reached. Tip Deflection 0 .48 V/div Z Position - 10.00 V/div Set p oint Retracting Extending Force Imaging 13-22 Dimension 3100 Manual Rev. B Obtaining a Good Force Curve continued. Force Imaging 13-22 Dimension 3100 Manual Rev. B Obtaining a Good Force Curve continued Figure 13.5d Adjusted Force Curve. effect of pushing the cantilever farther up before the Setpoint is reached. Tip Deflection 0 .48 V/div Z Position - 10.00 V/div Set p oint Retracting Extending