Fluid Operation
TappingMode in Fluids
134
MultiMode SPM Instruction Manual
Rev. B
8.3
TappingMode in Fluids
Operation of TappingMode in
fl
uid provides the same advantages of TappingMode in air, with the
additional ability to image samples under native liquid conditions. In
fl
uid 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
fl
uid.
Note:
Before attempting TappingMode in
fl
uids, it is recommended that the user
becomes familiar with standard TappingMode operation in air (see
and Contact Mode in
fl
uid.
8.3.1 Procedure for TappingMode Imaging in Fluid
1. Follow the directions described in the Contact Mode section (see
)
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
>
Pro
fi
le
and choose a TappingMode pro
fi
le.
•
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-de
fi
ned 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
fl
uid is a broad peak centered
around 10kHz (see
). 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.
