Scanning Tunneling Microscopy (STM)
Troubleshooting for STM
Rev. B
MultiMode SPM Instruction Manual
155
9.4
Troubleshooting for STM
This section addresses errors or malfunctions encountered during the operation of the MultiMode
as an STM. See
in this manual for additional troubleshooting tips.
9.4.1 Head and Microscope-related Problems
This section deals with problems related to the scanners or the microscope. If a problem exists with
a scanner, try a second one under the same conditions, if possible. Otherwise, the following list of
symptoms and cures may be helpful:
Table 9.4a
Head and Microscope Troubleshooting
Head/Tip Problem
Troubleshooting Tip
Head Engages
Immediately
If the STM engages immediately after initiating the
Motor
>
Engage
command, then one of the
following probably occurred:
Tip on surface
Make sure the tip is not touching the surface of the sample. Adjust the coarse-adjustment screws
upward until the tip is far from the surface.
Controller off
Verify that power to the controller is on and that the controller is connected to the computer
workstation via the beige 25-pin cable.
MultiMode base switch not
set for
STM
Verify that the switch on the left side of the MultiMode base is toggled to
STM
.
Disconnected
Verify that the 15-pin microconnector from the head is plugged into the microscope and the
microscope is plugged into the controller.
Tip Never Engages
If the tip never engages, test for the following:
Disconnected
Make sure the microscope is connected to the controller.
Binding on drive screw
Feel the rear, motor-driven adjustment screw during engagement to verify that it is rotating. If
the motion is erratic, then the screw is fouled with debris and binding. Remove the screw, clean
threads and regrease per instructions provided in
Vertical Engagement Scanners—Installa-
Bias shorted
Measure the bias by using a voltmeter between the head and stage chuck. If this is not in agree-
ment with the settings in the
Bias
voltage item in the STM Parameter control panel and appears
to be grounded, then check to see if anything is providing a conduction path between the Base
and the Base Support or any other ground.
Bias not applied to sample
surface
In some cases the sample consists of a layer of electrically conductive material on top of an insu-
lator. A conduction path must be provided between the sample puck and the sample surface.
Carbon glue or silver epoxy can be used to connect the bias voltage to the sample surface.
Tip Crashes
If the tip always crashes into the surface with the
Z Center Position
either changing erratically
or stuck in the fully retracted position, try the following:
