Problem with PFE de-focusing transect points

[Anette von der Handt]

Hi,

I have a recurring issue with PFE defocusing sample positions in a transect from the second position on-wards once in a while.

An example as it just happened again:

Original position file, set through digitize transect

     X                 Y            Z
72.444      50.4061      9.9455
72.44424  50.40808    9.945379
72.44449  50.41007    9.945258
72.44473  50.41205    9.945137
72.44498  50.41404    9.945016

Actually acquired positions
    X                Y                   Z   
72.4439    50.4060      9.94550
72.4442    50.4082      9.99550   
72.4444    50.4104      9.99550      
72.4446    50.4124      9.99500
72.4449    50.4143      9.99500

This happens occasionally but not reproducible. It only occurs during transects and always from the second point onward (and of course screws up all the data). I have seen it happen "live" once where the defocusing occurs after the backlash and acts as if the stage "skipped" its position. However, all the positions in the following samples are ok again and it seems that it gets "stuck" at this Z position for the remainder of the transect (all Z being identical)

Does anyone else have the problem (JEOL8900 here)? John, any ideas?

Thank you!

[John Donovan]

I have a recurring issue with PFE defocusing sample positions in a transect from the second position on-wards once in a while.
This happens occasionally but not reproducible. It only occurs during transects and always from the second point onward (and of course screws up all the data). I have seen it happen "live" once where the defocusing occurs after the backlash and acts as if the stage "skipped" its position. However, all the positions in the following samples are ok again and it seems that it gets "stuck" at this Z position for the remainder of the transect (all Z being identical)

Does anyone else have the problem (JEOL8900 here)? John, any ideas?

Hi Anette,
PFE records the actual current stage position during acquisition.

So if your stage doesn't actually move because the distance is too small to cause a real change in your stage position, the actual current position is recorded instead of the calculated position.

This is the most "honest" acquisition, yes?

I suggest that if you are attempting to move very small distances during your acquisition, that you utilize the beam deflection method as that will then record the actual change in beam position which is more precise than stage movement.

This is basically a hardware limitation.
john

[Anette von der Handt]

Sorry, I should I have made it more clear in the example what I am getting at.  What I tried to point out here is that the Z position jumps from 9.94550 to 9.99550 between the first and second point contrary to what was programmed.

The stage is definitely moving, including a backlash, between the individual points. This specific example has indeed a very small step size but I had it happen at much larger steps as well (but I would have to do some digging to find good examples while I had this one at hand).

In the past, when I caught it in time and the sample was still in the machine and check, I could also see every time that the first point of the transect was focused and all subsequent points were defocused.

I'll see if I can find more examples at varying step sizes of this behavior.

Anette

[John Donovan]

Sorry, I should I have made it more clear in the example what I am getting at.  What I tried to point out here is that the Z position jumps from 9.94550 to 9.99550 between the first and second point contrary to what was programmed.

The stage is definitely moving, including a backlash, between the individual points. This specific example has indeed a very small step size but I had it happen at much larger steps as well (but I would have to do some digging to find good examples while I had this one at hand).

In the past, when I caught it in time and the sample was still in the machine and check, I could also see every time that the first point of the transect was focused and all subsequent points were defocused.

Hi Anette,
This is a stage hardware problem.  Please call your service person.
john