10/27/97

I am experiencing an excessive charging in my SEM. The tested samples

are conductive, the specimen mount, holder and SEM stage are all well

grounded, but charging persists, precluding succesful imaging. Secondary

and backscattered electron images are equally affected. These samples

do not exhibit charging when analyzed under the same conditions (AV) in

another SEM. Many different samples were tested in these two SEMs and

the results are consistent.

It appears that some instrumental factor is involved. I would

appreciate the input on the subject. Thank you very much in advance.

Chris Terlecki

Applied Analytical Sciences

ph: 714-434-6894

email: aas@pacbell.net

If indeed the specimen and stage are grounded, you should check that you

are not using excessive beam current. Also, a large condenser spot or a

huge final aperture can be the problem. Since BS too is affected grounding

of the scintillator cannot be the problem.

If a bare specimen mount does not charge, then the specimen itself is

likely the problem. The other SEM may use just a little less beam current

and a partially conducting specimen would then not charge up.

If the problem is specimen related, one of the more common problems would

be the umbrella effect;

where the specimen is well coated on the upper surfaces, but these surfaces

prevent a continuos good coating on the under sides. Visualise a stack of

cannon balls or a mushroom: Coating from above would not be effective.

Such specimens can be sputter coated by laying the pin type mount on the

side, coating and then turning the specimen on the opposite side of the

pine and giving it a second coating.

At least this is a more interesting problem then fiddling with digital

files. Oh, did you use that address "experts" deliberately? I understand

the word means 'squirt under pressure'.

Cheers

Jim Darley

ProSciTech Microscopy PLUS

PO Box 111, Thuringowa QLD 4817 Australia

Phone +61 77 740 370 Fax: +61 77 892 313

Great microscopy catalogue, 500 Links, MSDS, User Notes

************************ http://www.proscitech.com.au

----------

images. You first need to really determine if it is the specimen or SEM.

Same effect with entirely different specimens? If you move the same

specimen between the different SEMs, is it always only in the one SEM? Use

scan rotation - does the effect stay with the specimen or move with the

scan direction. I guess I'd suspect some fault in the scan generation if it

is really to do with the SEM - electrical fault in scan generation, or

fault in coils, or connection to coils?

Regards,

--

Larry Stoter

17, Rocks Park Road, Uckfield, E. Sussex, TN22 2AT, UK

email: LPS@teknesis.demon.co.uk

Phone/Fax: +44 (0)1825 767967

I presume that for some reason you cannot coat the sample even though

they are conductive. A wiff ie 5nm AuPd on the surface should overcome

the charging. Also, turn down the wick on your microscope ie low kV, low

beam current.

Patrick Echlin

Cambridge

pe13@cus.cam.ac.uk

capable of measuring the absrobed current, see if that is operating

normally. A disconnected wire to ground from the stage will cause any

sample to charge. Check continuity between the stage and the microscope

body. Move the stage around while checking; you may have an intermitten

contact.

-Scott Walck

walck@ppg.com

contamination. A small bit of insulating material at the final

lens or in the column can deflect (often erratically) the incident

beam.

Woody White, Electron Microscopist SEM/EDS/WDS

Work: Mcdermott Technology, Inc.

woody.n.white@mcdermott.com

http://www.mtiresearch.com/