Fluid Operation
TappingMode in Fluids
136
MultiMode SPM Instruction Manual
Rev. B
•
Adjust and optimize these settings for each imaging condition and sample.
6. Center the laser spot on the photodiode detector.
•
Adjust the photodiode until de
fl
ection is roughly zero.
•
The de
fl
ection signal can drift when the probe is
fi
rst in
fl
uid, so it is best to adjust just
prior to engaging.
7. Click the
Engage
icon
to bring the tip into tapping range.
•
The NanoScope software automatically selects a setpoint, then stops the engagement
when the surface is detected.
8. Adjust the setpoint when engaged.
•
The best topographic images are usually obtained at setpoints 10-20 percent less than
the RMS amplitude before engaging.
•
The setpoint may be optimized using the
Force Cal
(
View
>
Force Mode
>
Calibrate
)
command and by optimizing the image quality. Both techniques are described in the
next section.
•
It may be necessary to check the cantilever tune after engaging. Select
View
>
Sweep
>
Cantilever Tune
. When prompted for a
Tip Offset
, enter
100-200nm
. Observe the
cantilever tune spectrum and the offset drive frequency if required.
8.3.2 Plotting Amplitude vs. Distance (Force Cal Curve)
The
View
>
Force Mode
>
Calibrate
command plots the cantilever oscillation amplitude versus
the sample position. The curve shows a mostly
fl
at region where the probe has not yet reached the
surface and a sloped region where the amplitude is being reduced by the tapping interaction.
1. Set up
Force Calibrate
as described for TappingMode in air (experienced users may prefer
the
Force Step
command instead).
2. Adjust the setpoint until the green setpoint line on the graph is just barely below the flat
region of the Force Cal curve.
•
This setpoint applies the lowest force to the sample.
CAUTION:
To protect the tip and sample, do not reduce the cantilever
oscillation amplitude to zero.
