Ch. 6. Fluid Imaging in a Droplet Sec. 6.4. Imaging with the Droplet Holder
has false engaged and you should check the tuning of the lever and adjust as necessary. If you see the Z
control voltage move to a value and stop then you most likely have correctly engaged. Begin scanning.
Tip
One useful thing is to monitor the deflection signal. Normally the deflection signal
is not shown since the feedback signal is the Amplitude. Monitoring the deflection
signal is helpful because in some cases the deflection will jump up as though the
tip is has engaged in contact mode when the amplitude is falling. If this happens it
indicates that the amplitude signal may be the result of deflections from the
droplet holder components themselves resonating or the cantilever bending in a
way that produces angular motion of the optical spot and not the result of the
cantilever flexing at the tip end. If you see the deflection signal changing as
though it’s engaging in contact mode then most likely you should re-tune the
system and try driving the lever at a different frequency (choose a different peak).
This behavior is the result of using low spring constant cantilevers. Stiffer levers
typically do not do this.
To display the deflection signal, click on the ’Setup’ button in the Sum and
Deflection meter panel. Change the deflection from Auto to Show.
Tip
Do a force curve and monitor the amplitude signal. The amplitude signal should
show an abrupt drop to 0 volts just before tip contact is made. Doing a force curve
is equivalent to seeing the conditions of the last engage cycle during the tip
approach.
1.
Adding additional fluid during scanning
During the experiment, you may find that the
tip develops a tendency to float off the
surface. This may be due to evaporation
causing a loss of fluid volume which directly
affects the AC drive oscillating the cantilever.
If you suspect this has happening, use a
pipette to add additional fluid to the
tip/sample area and re-tune the system.
2.
After scanning
• After you are finished scanning move
the focus offset ring on the objective
back to 0mm.
BETA
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