Electron Microscope Focus Problem
 

The image of our Amray SEM has a horizontal band across the center
third of the image which is slightly out of focus. The top and bottom
thirds are fine. This machine, while being fairly old, is new to our
institution and I believe some of the maintenance practices have
lapsed. I was wondering if it was possible that a weak filament or
contaminated optical column or dirty apertures could cause a problem
like this.

Any advice would be appreciated.

Thanks.
Gary

Electron Microscope Focus Problem
 

"Mac" writes:

The image of our Amray SEM has a horizontal band across the center
third of the image which is slightly out of focus. The top and bottom
thirds are fine. This machine, while being fairly old, is new to our
institution and I believe some of the maintenance practices have
lapsed. I was wondering if it was possible that a weak filament or
contaminated optical column or dirty apertures could cause a problem
like this.

Is it affected by settings like magnification? Have you ruled out stupid
stuff like the video monitor itself? :) Is the change in focus sudden
(with respect to vertical location) or gradual? Have you looked at any
of the signals that control focus?

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Electron Microscope Focus Problem
 

The problem is only evident in the 400 to 1200 magnification range. The
change in focus does seem to be sudden. We ruled out the video monitor
on the basis that the image is digitized on a computer as well as being
sent to the monitor of the SEM and both show the focus problem. We
haven't as yet started looking focus control signals. At this point
I'm trying to get a feel for whether the lack of maintenance could be
the problem or an electronic failure.

Thanks,
Gary

Electron Microscope Focus Problem
 

How about a wild guess, something needs degaussing?

Mac wrote:

The problem is only evident in the 400 to 1200 magnification range. The
change in focus does seem to be sudden. We ruled out the video monitor
on the basis that the image is digitized on a computer as well as being
sent to the monitor of the SEM and both show the focus problem. We
haven't as yet started looking focus control signals. At this point
I'm trying to get a feel for whether the lack of maintenance could be
the problem or an electronic failure.

Thanks,
Gary




--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P

Electron Microscope Focus Problem
 

Mac wrote:
The image of our Amray SEM has a horizontal band across the center
third of the image which is slightly out of focus. The top and bottom
thirds are fine. This machine, while being fairly old, is new to our
institution and I believe some of the maintenance practices have
lapsed. I was wondering if it was possible that a weak filament or
contaminated optical column or dirty apertures could cause a problem
like this.

Any advice would be appreciated.

Thanks.
Gary

Is this at TV-Scan rate and Slow scan too ! What is the specimen being
examined, This is behaving like a Charging artifact. Try another type of
specimen, Sounds more like a specimen charging problem to me. What is
the Accelerating Voltage. Dirty Column and apertures usually just cause
astigmatism problems


Yukio YANO

Retired SEM Tech.

Electron Microscope Focus Problem
 

Our operator doesn't use the TV-scan, only the slow scan. Her
specimens are organic. She is familiar with what a charging artifact
produces on the system. She describes it as horizontal streaks across
the image at which point she deposits more gold on the specimen to
correct the charging problem. This problem is a very subtle focus
issue in a horizontal band across the center of the image. The band
takes up acout 1/3 to 1/2 of the image in width. The accelerating
voltage is 15KV.

I have an image showing the problem at the following link:

www.noobie.ca/tmp/blurry.jpg

Thanks,
Gary

Electron Microscope Focus Problem
 

"Mac" writes:

Our operator doesn't use the TV-scan, only the slow scan. Her
specimens are organic. She is familiar with what a charging artifact
produces on the system. She describes it as horizontal streaks across
the image at which point she deposits more gold on the specimen to
correct the charging problem. This problem is a very subtle focus
issue in a horizontal band across the center of the image. The band
takes up acout 1/3 to 1/2 of the image in width. The accelerating
voltage is 15KV.

I have an image showing the problem at the following link:

www.noobie.ca/tmp/blurry.jpg

Wow, that doesn't exactly jump out at you!

Is the location/severity magnification dependent?

What does adjusting the focus of the microscope actually do to the image?

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Electron Microscope Focus Problem
 

Mac wrote:
Our operator doesn't use the TV-scan, only the slow scan. Her
specimens are organic. She is familiar with what a charging artifact
produces on the system. She describes it as horizontal streaks across
the image at which point she deposits more gold on the specimen to
correct the charging problem. This problem is a very subtle focus
issue in a horizontal band across the center of the image. The band
takes up acout 1/3 to 1/2 of the image in width. The accelerating
voltage is 15KV.

I have an image showing the problem at the following link:

www.noobie.ca/tmp/blurry.jpg

Thanks,
Gary

My Long Stare makes me wonder if I am looking at a small fibre strand in
the Column!

My next step would be to use a "ANOPORE Filter" as a Test object I
think 0.01 micron would be best, although 0.2 micron would do. Check
with the Biology Department for a sample. I think I would have
recommended it for sample preparation where dehydration on a membrane
filter was indicated.

This is an Aluminum Oxide Filter Media that I used for a High Mag Test
Object Sputter Coat a fragment bonded to a stub using Double-coated Tape.

This will Give you an extremely Uniform Mesh that will allow you to see
Focus/astigmatism problems over the entire Field of View.

I suspect that at lower Magnification~ 400X, a small segment will show
a localized area of astigmatism, (dirty side of Column)
At a higher Magnification ~ 1500/2500X the majority of
the field would be astigmatic as the beam would sweep across a smaller
and smaller portion of the Column, or maybe asymptomatic as it sweeps
across an unaffected part of the column.

Anyway I don't really think it is an Electronic Problem, more likely
Housekeeping, "Contaminated Liner Tube", Scrub with Aluminum Oxide. The
Microtombe people use it for Polishing their Knives, and its cheaper
than "Wenol".

Yukio YANO

Electron Microscope Focus Problem
 

Yukio YANO wrote:
Mac wrote:
Our operator doesn't use the TV-scan, only the slow scan. Her
specimens are organic. She is familiar with what a charging artifact
produces on the system. She describes it as horizontal streaks across
the image at which point she deposits more gold on the specimen to
correct the charging problem. This problem is a very subtle focus
issue in a horizontal band across the center of the image. The band
takes up acout 1/3 to 1/2 of the image in width. The accelerating
voltage is 15KV.

I have an image showing the problem at the following link:

www.noobie.ca/tmp/blurry.jpg

Thanks,
Gary

My Long Stare makes me wonder if I am looking at a small fibre strand in
the Column!

My next step would be to use a "ANOPORE Filter" as a Test object I
think 0.01 micron would be best, although 0.2 micron would do. Check
with the Biology Department for a sample. I think I would have
recommended it for sample preparation where dehydration on a membrane
filter was indicated.

This is an Aluminum Oxide Filter Media that I used for a High Mag Test
Object Sputter Coat a fragment bonded to a stub using Double-coated Tape.

This will Give you an extremely Uniform Mesh that will allow you to see
Focus/astigmatism problems over the entire Field of View.

I suspect that at lower Magnification~ 400X, a small segment will show
a localized area of astigmatism, (dirty side of Column)
At a higher Magnification ~ 1500/2500X the majority of
the field would be astigmatic as the beam would sweep across a smaller
and smaller portion of the Column, or maybe asymptomatic as it sweeps
across an unaffected part of the column.

Anyway I don't really think it is an Electronic Problem, more likely
Housekeeping, "Contaminated Liner Tube", Scrub with Aluminum Oxide. The
Microtombe people use it for Polishing their Knives, and its cheaper
than "Wenol".

Yukio YANO

Electron Microscope Focus Problem
 

I am the operator of this SEM in question, so I thought it might be
helpful if I joined in on the group.
I am currently using the largest spot size to image my specimens - do
you suspect any connection with this to my problem?
I will plan to obtain a test object such as the one you mentioned and
image it to check for focu/astigmatism problems.
Thanks for your advice.
Glenda

Electron Microscope Focus Problem