Force Imaging
Force Calibration Control Panels and Menus
Rev. B
MultiMode SPM Instruction Manual
187
11.3.4 Feedback Controls Panel
All of the parameters in the
Feedback
Controls
panel also affect
Image
mode.
De
fl
ection Setpoint (Contact Mode)
By changing the de
fl
ection setpoint, you can adjust the cantilever de
fl
ection voltage maintained by
the feedback loop in
Image
mode. This parameter de
fi
nes the center of the range of Cantilever
De
fl
ection Voltages that can be collected. If the
Data Center
=
0
, then the setpoint is at the center
line of the force plot shown on the display monitor. Changing the setpoint shifts the force
calibration curve on the graph. For example, if the setpoint is set to -3.0V and the data center is 0,
the cantilever de
fl
ection axis of the graph centers around -3.0V. Raising the setpoint to -2.0V shifts
the force calibration curve down by one volt so the graph centers at -2.0V. Changing the value of
this parameter in
Force Calibration
mode also changes the
Image
mode.
Amplitude Setpoint (TappingMode)
The RMS value of the cantilever de
fl
ection voltage maintained by the feedback loop in
Image
mode can be adjusted by changing
Setpoint
. In a TappingMode force plot
mode, the setpoint
de
fi
nes the centerline of the vertical, “Amplitude” axis of the amplitude calibration plot shown on
the display monitor (the Data Center must be 0 for that Channel). Changing the
Setpoint
shifts the
amplitude curve on the graph. For example, if the setpoint is at 3.0V, the RMS amplitude axis of the
graph will be centered around 3.0V; raising the setpoint to 4.0V will shift the amplitude curve down
by one volt, so the graph will be centered at 4.0V. Changing the value of this parameter in the
Amplitude Calibration
mode also changes the setpoint parameter in
Image
mode.
De
fl
ection/Amplitude Limit
This parameter changes the gain applied to the input signal. You can reduce the input signal by a
factor of eight for a NanoScope IIIa (or set it to one of seven different levels for a NanoScope IV) to
see more of the
Force Calibration
plot de
fl
ection or amplitude. This parameter also affects
Image
mode and the resolution of the system; therefore, change the value to
2.5V
for a NanoScope IIIa (or
5V for a NanoScope IV) before returning to imaging.
Drive Frequency (TappingMode)
This parameter de
fi
nes the frequency at which the cantilever is vibrated. This frequency should be
close to the resonant frequency of the cantilever. Changing the value of this parameter in the
Force
Plot
menu also changes the
Drive frequency
parameter in the
Image
mode.
Drive Amplitude (TappingMode AFM)
This parameter de
fi
nes the amplitude of the voltage applied to the piezo system which drives the
cantilever vibration. Changing the value of this parameter in
Force Plot
mode also changes the
Drive amplitude
parameter in the
Image
mode.
