Calibration, Maintenance, Troubleshooting and Warranty
Contact AFM Troubleshooting
314
MultiMode SPM Instruction Manual
Rev. B
•
Check the cabling between the computer and the controller, and between the controller
and the microscope. Any discontinuity in the microscope signals can cause an
immediate engage.
•
The
Setpoint
may be set more negative than the vertical de
fl
ection (A-B) voltage (this
applies only to contact AFM modes). This false engagement is immediate and the
computer will not show any motor travel or time delay after one gives the command. To
correct for this condition, select
Withdraw
and check that the vertical de
fl
ection
voltage reads a voltage more negative than the setpoint voltage.
•
Static charge from the sample.
15.11.2
Head appears engaged but does not track surface features
Occasionally, the head appears to be engaged but surface features do not appear on the display
monitor. This usually results from false engagement (see
above), poor laser
alignment, or something other than the tip coming in contact with the sample surface.
An easy way to check for laser alignment problems is to check the laser beam using a magni
fi
er or
slip of paper. Click on the
Withdraw
command to remove the cantilever from the surface and
recheck alignment with the magni
fi
er or paper method (see
). When satis
fi
ed with the
alignment, readjust the vertical de
fl
ection voltage before re-attempting engagement.
Occasionally, when the optical head is not leveled properly, something other than the cantilever tip
(usually the corner of the substrate or the cantilever clip) will contact the surface during
engagement. The system may engage, but the image will not contain any features. Testing the SUM
signal after withdrawing the tip several times is a good test for this failure mode. Generally, the
SUM signal will be far from its original value if something other than the tip contacts the surface.
The head should be leveled and the laser realigned if this has occurred.
15.11.3
Head does not engage
The complementary problem to false engagement is not engaging at all. Here are some common
causes of this problem:
•
The tip may have started too far from the sample. Lower the tip’s height above the
sample surface by using the coarse alignment screws, then repeat the engagement
procedure.
•
The laser may be misaligned and/or the cantilever may be broken. When this occurs,
replace the cantilever substrate, realign the laser, and repeat the engagement procedure.
