BSE image "streaking"

[John Donovan]

I occasionally notice random pixels in the BSE image on my SX100 that seem to cause horizontal "streaks" as seen here:



Does anyone know what causes this and how to prevent this from happening?

It does *not* seem to be a function of contrast or brightness and might be worse at higher beam voltages (i.e., 20 keV rather than 10 keV), but I haven't done any real testing.

[John Donovan]

Ok, here's more data. It does appear to be related to the electron beam energy. Here's a BSE image at 20 keV:



Now here's one at 16 keV:



And here's one at 10 keV:



All at the same beam current (50 nA).

Any suggestions on what we can do to fix this?
john

[John Donovan]

Update on the BSE streaking in the above images.

We see these single pixel streaks in both BSE and SE images and we see them in the BSE image even if the SE detector is off.

We're cleaning the whenelt in case that is somehow causing this at higher gun voltages.

[Probeman]

Cleaning the Whenelt *did* help quite a bit.  This is after cleaning and with the gain turned up to 800 or so.



We'll try replacing the filament.

[Probeman]

So here is another imaging artifact that I am seeing on our SX100 at UofO (see attachments below).  The color image is the original mosaic that was posted here:

http://probesoftware.com/smf/index.php?topic=324.msg1700#msg1700

And the other attachment is the same image as grey scale with annotations showing the approximate gray levels (0 to 255).

You will note two varieties of "gradients" in the right to left direction (the fast beam scan direction). The first gradient notated with the two inner values corresponding to the left and right sides of most of the sub images, and the second gradient notated with the two outer values corresponding to the left and right sides of the whole mosaic.

My first question is why are we getting these gradients?  Note that the "ground" BSE mode was used with a very low contrast (~120) so we are not over driving the BSE amp for sure.

The next question is why are the two gradients of opposite polarities? That is to say, the sub image gradient goes left to right and dark to light, while the mosaic gradient goes left to right and light to dark!

The last question is: has any one seen similar "gradients" on their instrument?

I would be interested to hear your ideas on what might be causing these artifacts and how to reduce them?  Are the BSE diodes "unbalanced", dirty, what?

[Philipp Poeml]

I think we have pretty much similar gradients. I need to check on some mosaics for details. Gradients we do have in both SE and BSE, I need to verify the directions.