Instruction manual

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.
Deflection Setpoint (Contact Mode)
By changing the deflection setpoint, you can adjust the cantilever deflection voltage maintained by
the feedback loop in Image mode. This parameter defines the center of the range of Cantilever
Deflection 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 deflection 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 deflection voltage maintained by the feedback loop in Image
mode can be adjusted by changing Setpoint. In a TappingMode force plot mode, the setpoint
defines 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.
Deflection/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 deflection 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 defines 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 defines 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.