Adjustment of Cross Over point (green cross) (#85)

It can happen that the green cross used for "Source Tilt" adjustment ("Cross Over" activated) is not visible. This could be due to the calibration of this position has been erased for some reason.

If you try to adjust "Source Tilt" using the yellow cross in the center of the image, you will get no signal in most of the "spots".

To correct this there is a calibration procedure (# 85) available.

Please note that this procdure is ONLY to be carried out by Nanolab Managers.

  

These are the controls for the calibration.
  • Some instructions
  • Coordinates for the cross over point indicator
  • A "Gun Tilt" control with "Cross Over" activation button.
  • A "Calibration" button
  • Contrast and Brightness controls

The procedure always defaults to 30 kV and next but largest "spot". To make the calibration in the more normal voltage range, select 15 kV.

It is enough to do this calibration for one voltage only.

But still select the next but largest "spot". This will make the white dot rather small, thus making the calibration more precise.

When you start the calibration it can look like this

The Cross Over point (green cross) is set to the the center of the image, where the yellow cross always is.

Try to position the dot using the "Gun Tilt" control to a position roughly like this.

Then switch to normal image (stop "Crossover" mode, and try to maximize the intensity of the image using the "Gun Tilt" control. Switch the sensitivity of the control to "Fine" by right-clicking on the control.

For the high current spots the the dot is rather small and the adjustment can be difficult, but more precise.

When you have found the maximum intensity, switch back to "Crossover" mode and click on the "Calibration" button. The software will now find the bright dot and place the green cross over it.

Then click "Finish" button at the top right and the green cross should be correctly positioned for later "Source Tilt" adjustments.


Anders Liljeborg Albanova Nanolab, KTH, SU.