5
MEASUREMENT OPERATION
5-148
TMPM5200-2
•
Make sure that Loop Gain is not so low.
If Loop Gain is set to a low number, the gain of the feedback circuit is so small
that the feedback voltage is not applied up to the maximum voltage.
•
Make sure that the tunneling current is already flowing.
If Current/nA is set to a small value near 0 V, noise or a similar component may
be mistaken for a tunneling current, thus resulting in performing no approach-
ing (the computer judges that approaching has been completed). In such a case,
specify a larger value for Current/nA; then try to find a Current/nA value where
the Z voltage becomes the largest.
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4.
Click on the Approach On button on the Tip window.
The motor for approaching starts to rotate and automatically stops when the tunnel-
ing current becomes the same as the value given in Current/nA.
may hear an oscillation sound coming from the instrument when approachi
completing. This is because the setting of the feedback filter is so fast that it oscillates. If
ound continues, click on the
button in the Feedback Filter/Hz selection box, and
then select a slow filter (a smaller value) from the pull-down menu.
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Topography image observation
When approaching has completed, carry out scanning.
Starting scanning
Click on the Repeat button on the Advanced tab window of the SPM
Parameters window.
Scanning will start and an image will appear in the Display Window.
In the case of the STM mode, an important factor for obtaining a quality image is
the setting of bias voltage and tunneling current. If this setting is inappropriate, not
only can a quality image not be obtained, but also the specimen and the tip may be
damaged.
Setting Sample Bias and Current/nA
You can control the distance between the specimen surface and the tip by adjusting
Sample Bias and Current/nA.
If Sample Bias is set to a small value and Current/nA to a large value, the distance
between the specimen surface and the tip becomes short. Theoretically, the resolving
power improves, but the tip could easily collide with the specimen.
—— CAUTION ———————
If the Sample Bias is set by using the slider during image observa-
tion, be careful not to move the slider button across 0 V. The tip
would collide with the specimen surface if the bias voltage became
0 (zero).