Instruction manual

Calibration, Maintenance, Troubleshooting and Warranty
Contact AFM Troubleshooting
Rev. B MultiMode SPM Instruction Manual 315
15.11.4 Head engages immediately
If the microscope engages immediately after the Engage icon is selected, the problem may be one
the following: 1) The Setpoint may be lower than the feedback voltage. Select Withdraw a few
times and verify that the vertical deflection reads a negative voltage of -1.0 to -4.0V. Adjust the
Setpoint to zero or slightly above and try to engage again. If the microscope still engages
immediately, check the cabling between the computer and the NanoScope controller and also
between the controller and the microscope. Any discontinuity in the voltage feedback will cause an
immediate engage.
15.11.5 Displacement of material
This is generally caused by too much tracking force. Use the Force Calibration window after
engagement for setting the correct tracking force.
The AFM can be tuned to operate in the attractive region of the force curve. This will take
advantage of the fluid layer which captures and holds the tip to the sample. This effectively reduces
the tracking force. Be aware of the fact that this means the tip is pulling away from the sample. This
operating condition might cause the tip to pop off of the sample surface.
15.11.6 Lines in the image
Lines can be caused by:
• AFM tip picking up contamination. The tip will effectively become longer and this will
cause the feedback loop to raise the tip to keep the same tracking force. The
contamination can come off of the tip which will cause another level shift in the image.
This problem will show up as large bands in the captured image.
• Friction. Some samples have a stronger frictional interaction with the tip than others.
The cantilever will bend and straighten due to the tip sticking and slipping as it is
dragged across the surface of the sample. The result is a line-by-line level shift in the
captured image. The trace and retrace scan directions can actually be inverted from each
other if the friction is high enough. A good practice is to use the scope image mode in
dual trace display. The trace and retrace directions should be close to each other. Trace
and retrace can invert if there is friction present between the tip and the sample surface.
15.11.7 Problems with silicon nitride cantilevers
Sometimes nitride cantilevers can be a problem due to lateral warping or torquing of the nitride
beams. This causes the reflected light to spill off to the side as the tip begins to engage the sample.
Warping or torquing of the cantilever is associated with some older cantilever wafers. If
engagement does not work the first time, try changing the actual lever used, i.e., go to the next lever
on the same chip. Usually, the wide 200µm-long lever has the most lateral warping. If this is the
case, try the wide, short cantilever next to it. Generally, the narrow-legged silicon nitride cantilevers