Instruction manual

Force Imaging
Force Modulation
Rev. B MultiMode SPM Instruction Manual 207
8. Find the Bimorph Resonant Frequency: The cantilever is oscillated by a small
piezoelectric bimorph mounted in the cantilever holder. For Force Modulation, oscillate the
bimorph at or near its resonant frequency. The bimorph resonance frequency is usually the
largest peak in the 5-30kHz range. This ensures the cantilever moves with sufficient
amplitude to produce elasticity contrast.
Note: You need to find the bimorph’s resonant frequency only once. (Resonant
frequencies are unique to each force modulation cantilever holder.) Once you
find the resonant frequency, write it down for future use. This Drive frequency
may be used as a starting place each time you perform force modulation
imaging; however, recheck the bimorph’s resonant frequency in free air using
Cantilever Tune each time you install a new cantilever.
a. Use a FESP or TESP cantilever. NP probes have confusing low frequency resonances.
b. Select View > Sweep > Cantilever Tune or click on the Cantilever Tune icon.
c. The display monitor plots the Frequency Sweep, showing cantilever oscillation
amplitude versus frequency. To set the parameters controlling the Frequency Sweep
plot, use the parameters in the Sweep Controls panel and the commands on the top
menu bar of the display monitor.
Figure 11.6c Auto Tune Controls Panel
d. Set the Drive frequency to 15kHz and the Sweep width to 30kHz.
e. Set the Drive amplitude at 1V to start. You can readjust this value later.
Note: A series of peaks display on the Frequency Sweep plot. A typical Frequency
Sweep plot is shown in Figure 11.6d.
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