Cantilever Tune

The Cantilever Tune command allows determination of the cantilever resonant frequency and the setting of the operating point for TappingMode feedback (see Figure 3.1t). Cantilever Tune sweeps the cantilever drive frequency over a selectable range, then displays plots of the cantilever amplitude and phase versus drive frequency. This command is enabled only when the Microscope mode parameter in the Other panel of the Scan Parameter List is set to Tapping. On Small Sample MultiMode SPMs, verify that the switch located on the base is toggled to TM AFM before selecting the Cantilever Tune command.

Figure 1 shows how the maximum amplitude is attained in air at the cantilever natural resonance. Figure 2 shows the amplitude is reduced when it is in contact with the sample surface.

Figure 1: Tapping cantilever in mid-air

Figure 2: Tapping cantilever on sample surface

In TappingMode, the optical lever technique reflects a laser beam off the back of the oscillating cantilever, thence to a segmented photodiode. The differential signal between the top and bottom photodiode segments provides a sensitive measure of cantilever deflection. As the sample is scanned, analog circuitry determines the RMS value of the rapidly changing cantilever deflection signal. The RMS value of the cantilever deflection signal corresponds to the amplitude of the cantilever oscillation. Changes in amplitude of the cantilever oscillation are controlled by the feedback system to track the sample surface.

Access the Cantilever Tune dialogue box, shown in Figure 3, by selecting the Tune icon or by selecting Cantilever Tune from the Microscope menu.

Figure 3: The Cantilever Tune dialog box

Select Cantilever Tune Dialog Box Definitions:

Auto Tune Parameters:

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