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Scanning Tunneling Microscopy (STM)

Troubleshooting Operation of STM

190 Dimension 3100 Manual Rev. D

resistance measurements. However, oxide and contamination layers on the sample surface can

make imaging very difﬁcult. Higher bias voltages are required for these types of samples.

Problems During Realtime Operation

This section deals with problems that are associated with the Realtime aspects of the NanoScope

software although they often point to the scanning head or microscope.

Image goes out of Range

If the Z center position tends to go out of range at the edges, top and bottom or right and left of the

scan, then try the following:

•Level Sample to Head—The Z center position is affected by sample tilt and the

Dimension head may be less tolerant of sample tilt due to its small vertical range

compared to the large, lateral scan range. Try leveling the head relative to the sample by

noting the trend in Z center position and adjusting the head tilt accordingly. The View >

Scope Mode with the Show slope option can also be very helpful in eliminating tilt

along the scan direction.

•Measure Coupling— A broken wire to one of the electrodes can cause this problem and

will usually result in a large, monotonic increase (or decrease) in Z center position from

the bottom of the scan to the top.

Z drift

If the Z center voltage tends to drift out of range rather quickly after the head is engaged, it may be

a result of the following:

1. Thermal Drift— Allow some time for the temperature to stabilize if the microscope and/or

scan head has been stored in a cold place overnight. Drift can be minimized by keeping the

STM in a thermally stable environment.

2. Tip not Tight—Make sure the tip is held tightly in the tip holder. Push and pull on the tip

with the tweezers to see that it is not loose. Increase the bend in the tip if the tip seems loose.

3. Sample Hold-Down—Verify that the sample is flat against the chuck and cannot move

vertically. This may be become problematic if the sample has been affixed using uncured,

conductive epoxy, and/or if foam adhesives are used.

Realtime Image Hides Features

If the Realtime image appears to be ﬂat, but captured images reveal detail, then try rotating the

sample 90° in the microscope. The Realtime image leveling software tends to hide features that are

parallel to the X-scan direction.

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