has feedback tests between steps so the approach will stop automatically when the feedback conditions
have been met.
Tip
Open the Oscilloscope and view the Topography and Current signals during the
approach.
Note
A false tip engage can occur when transients in the microscope caused by the motion are
picked up by the preamp and feedback loop. Sometimes delays need to be increased
between the scan head taking an approach step and when the R9 Software checks the
signals. Also, if the feedback loop is turned too slow, a false tip engage can occur. This is
because the software process watching as the tip extends exceeds the timeout limit.
Check the Topography and Current signals after the approach stops to be sure there was not a false tip
engage. If the Topography signal shows that the tip is still fully extended and the Current is still 0 nA, try
the Slow Approach again. Pressing the Approach button while already in range will not cause any further
steps to be taken.
3.5 Adjusting the Position with Single Steps
There are several reasons why the user should adjust the position of the scan head with single steps after
a successful approach. For example:
• Bipolar scan tubes behave more linearly when they are driven near the middle of their range.
• Scanning with an almost fully extended tube could cause the sample to drift out of feedback range.
• Scanning with the tube when it is nearly fully retracted could increase the chances that the tip makes
accidental contact with the sample.
• Thermal drift may bring the sample closer or further from the tip over time.
Use the Single Step In and Single Step Out Procedures to adjust the scan head's relative position as
needed. The tip's relative position can be seen on the Oscilloscope (if it is acquiring Topography) and
the Scan Area Window (on the Feedback Bar).
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