Instruction manual

Fluid Operation
TappingMode in Fluids
134 MultiMode SPM Instruction Manual Rev. B
8.3 TappingMode in Fluids
Operation of TappingMode in fluid provides the same advantages of TappingMode in air, with the
additional ability to image samples under native liquid conditions. In fluid TappingMode, the probe
is oscillated so that it only intermittently contacts the sample surface. This can reduce or eliminate
lateral forces that can damage soft or fragile samples in Contact Mode. The following sections
provide general instructions for TappingMode imaging in fluid.
Note: Before attempting TappingMode in fluids, it is recommended that the user
becomes familiar with standard TappingMode operation in air (see Chapter 7)
and Contact Mode in fluid.
8.3.1 Procedure for TappingMode Imaging in Fluid
1. Follow the directions described in the Contact Mode section (see Section 8.2.1 on page 125)
to clean the fluid cell and O-ring. clean and mount a probe and then the sample.
2. Align the laser on the free end of the cantilever portion of the probe.
3. Center the photodiode to give a deflection signal near 0V.
4. Set up the system for TappingMode operation.
• Select Microscope > Profile and choose a TappingMode profile.
• Set mode selection switch on left side of MultiMode base to TMAFM.
5. Manual Cantilever Tune: Enter the View > Sweep > Cantilever Tune menu to select a drive
frequency.
• This is similar to the Cantilever Tune process used for standard TappingMode in air.
Unlike operation in air, the cantilever resonance will be largely damped by liquid and
the AutoTune function cannot be used.
• When viewing a wide bandwidth cantilever tune sweep, observe that there is no single,
well-defined resonance peak, but, rather a number of broader maxima. Manually select
a peak.
Note: For the short, narrow Si
3
N
4
probe recommended for soft samples (e.g., models
DNPS or OTR4), the resonant frequency in fluid is a broad peak centered
around 10kHz (see Figure 8.3a). Best results are achieved by tuning the
cantilever to a peak between 7-12kHz. Higher and lower frequencies have also
been used depending on the type of probe employed. Start with a Sweep width
of 20kHz and a Drive frequency of 10kHz in the Sweep Controls menu.