Instruction manual

Force Imaging
Force Calibration (TappingMode)
200 MultiMode SPM Instruction Manual Rev. B
Figure 11.5a Piezo Extension Versus RMS Amplitude and Deflection
Figure 11.5a illustrates a two-channel TappingMode force plot. The vertical axes of the graphs
represent the amplitude (top) and TM deflection signal (bottom) of the cantilever. The position of
the Z piezo plots along the horizontal axis. Channel 1 (top) demonstrates how the cantilever
amplitude decreases as the tip moves closer to the sample. The plot represents the amplitude for one
complete extension-retraction cycle of the piezo. The Scan rate parameter in the Main Controls
panel defines the rate at which the piezo completes an extension-retraction cycle; therefore, the rate
at which new curves display. At point 1, the tip encounters the sample surface. Upon encountering
the surface, the tip oscillation amplitude decreases, dropping off as the tip moves closer to the
sample surface. Between points 1 and 2, voltage to the Z piezo is increased, bringing the tip about
50 nm closer to the surface. Over the same interval, the cantilever amplitude diminishes about 2
volts due to dampening effects.
Collecting a force plot on a hard sample and dividing the change in amplitude by the change in Z
piezo position gives the responsiveness of the electronics that measure the amplitude. The
Amplitude Sensitivity value in the Main Controls menu is the inverse of the responsiveness. You
can determine this value by using the mouse to draw a line parallel to the plot’s slope in the region
between points 1 and 2 where the tip amplitude dampens. Tip damping occurs as a result of
mechanical-acoustic coupling between the tip and sample. As the z piezo is extended further,
oscillation eventually ceases and the amplitude drops to zero (point 2).
For TappingMode in air on a hard sample, each nanometer decrease in the cantilever position
decreases the peak-to-peak vibration of the cantilever by two nanometers. Once the tip encounters
the sample surface, the oscillation amplitude of the cantilever decreases as the piezo is extended.
1
2
3
Piezo extension
Piezo retraction
Tip is clear of the surface
4
047
5
z - 10.00nm/div
z - 10.00nm/div