3/12/99
A student in the lab is looking at museum samples of dinosaur bones and
teeth on the SEM. He could get access to more samples if he could restore
them to their original condition ( ie, remove the gold). Is there a good
nondestructive way to do this?
Kim DeRuyter
Histology and Electron Microscopy Labs
University of Alaska Fairbanks
carbon instead of gold, and then ashing the carbon off with O2. Gold is tricky
to remove on most materials (I work mostly with semiconductors), but would be
very difficult to remove on dinosaur bones. (This is assuming your samples are
small enough to fit into an available asher or RIE tool). There are several
labs that could perform both the coating and ashing - let me know if you have
trouble locating one close to your area.
Lisa Montanaro
Consultant, MME
CMontana4@aol.com
surface and examine the casts in the SEM. This way there is no damage to
the original artifact. I had an anthropology grad student do this with
human teeth for his thesis research. He worked out a very inexpensive, low
tech, but reliable method to do the casting. He can be reached at the
following for full details of his method:
Dr. Chris Schmidt
Indianapolis University
cschmidt@indy.edu
Debby Sherman, Manager Phone: 765-494-6666
Microscopy Center in Agriculture FAX: 765-494-5896
Dept. of Botany & Plant Pathology E-mail: sherman@btny.purdue.edu
Purdue University
1057 Whistler Building
West Lafayette, IN 47907-1057
and would result in damage to some specimens. A very brief exposure to NaCN
with a stronger oxidant such as ammonium persulfate or hydrogen peroxide
would probably accomplish the result without prolonged exposure to the
reagents which would lead to their becoming more deeply absorbed into
capillaries that may exist.
John Twilley
Conservation Scientist
jtwilley@sprynet.com
I seem to remember a story - a long time ago - about about dipping the sample in
liquid mercury - the gold is taken into the liquid as an amalgam and leaves the
specimen clean. I have never tried it. I do not know what any Safety person would
say about that these days!
Keith Ryan
Marine Biological Association of the UK
Citadel Hill
Plymouth
Devon PL1 2PB
England
Tel. 0044 1752 633249 (International)
Tel. 01752 633294 (National)
Fax. 0044 1752 633102 (International)
Fax. 01752 633102 (National)
e-mail: k.ryan@pml.ac.uk
One thing that no one has mentioned, yet, is low kV operation. If
your instrument will operate at 5kV or lower (perferably around 1kV) and
you limit your beam current, you should be able to view uncoated
specimens at at least a couple of kX. Some intruments will go much
higher at that voltage range. Grains of quartz may still present a
problem because SiO2 is such a good insulator, but many other minerals
will work fine under those conditions.
Ken Converse
owner
Quality Images
third party SEM service
Delta, PA
qualityimages@netrax.net
an old method which I used a long while ago and now and then recently
to remove gold from calcareous surfaces of REM-samples is to leave
the sample in a solution of NaCN and NaOH and let air bubble through
by means of a small glass pipette. The amount of NaCN is about 1-2%
and NaOH should be 1 N or more. You may try it on a fresh part of
bone perhaps it works.
Dietmar Keyser
PLEASE NOTE THE CHANGE IN TELEFON AND FAX
Dr.Dietmar Keyser
Zoologisches Institut und Museum
Martin-Luther-King Platz 3
D-20146 Hamburg
Germany
Tel. +49 40/428 38 4232
Fax: +49 40/428 38 3937
E-mail: Keyser@zoologie.uni-hamburg.de
casting procedure for your facility. I can give you the e-mail
address for Dr Robert Pastor who can let you know which resin
materials he used, but he used two ... one for the field while
casting the pliable negative mold of ancient Pakastani teeth,
and another casting resin for the durable positive mold in the
lab. You'd then be able to coat with gold and archive these
specimens for all types of future study ... and I was quite
impressed with the detail of the micr-wear and lack of artifacts.
cheerios, shAf
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Michael Shaffer, R.A. - ICQ 210524
Geological Science's Electron Probe Facility - University of Oregon
mshaf@darkwing.uoregon.edu - http://darkwing.uoregon.edu/~mshaf/
would be easier but basically its the same problem. C
coating is good enough for low powers, but again, Curators
do not like that dark coating,
To view these "hard, dry and non-conducting" specimens
uncoated, the best solution is a poor vacuum SEM; a fully
fledged Environmental SEM would also do well, but its a
more expensive instrument for that job. Poor vacuum SEM's
(I believe at least a couple of the major manufacturers
make instruments with that facility) use only mechanical
pump vacuum in the specimen chamber and because of a vacuum
limiting aperture retain high vacuum in the gun chamber.
Secondary mode is impossible, but a Robinson detector gives
excellent images for this type of work. Magnifications
under these conditions are limited to about 2000x, but
details in fossils do not warrant higher magnifications;
its the SEM's superior depths of field that wins out over
light microscopy.
Kim - all you require now is one of those scopes!
Years ago I modified an Etec Autoscan to function
reversibly as a poor vacuum instruments. It worked well but
it was a fair bit of trouble to accomplish the required
modifications.
Our online contain a link to an archive collated by Scott
Wight. This contains listserver contributions concerned
with Environmental and Poor Vacuum SEM.
Cheers
Jim Darley
ProSciTech Microscopy
PLUS
PO Box 111, Thuringowa QLD 4817 Australia
Phone +61 7 4774 0370 Fax: +61 7 4789 2313
Great microscopy catalogue, 500 Links, MSDS, User Notes
********************** www.proscitech.com.au *****
taxonomic type specimens, fossils etc is to leave it off in the first place where
possible. The material can sometimes be viewed in a normal SEM by keeping kV
and probe current low, or generally more conveniently by using one of several types
of variable pressure SEM. Until recently the cheaper versions, working up to about
2 torr, were restricted to non-SE detection modes (BSE, CL, absorbed current etc)
but several SE detector systems working in this range have become commercially
available.
We have just installed a new Robinson detector which allows convenient BSE
and/or SE detection to low kV, in high vacuum or variable pressure conditions, on a
small Hitachi NSEM. (1992) and find the combination mode in particular gives very
good results for topographic imaging.
beats explaining a caustic cyanide stew to your friendly curator, I should think.
cheers
Sally
Dr Sally Stowe
Facility Coordinator
Australian National University EM Unit
Research School of Biological Sciences
Box 475,
ACT 2601, Canberra, Australia
FAX 06 (0)2 6279 8525
Especially for insects have a look at:
C. Arno': Removal of gold coatings from biological SEM specimens,
European Microscopy and Analysis, July 1998, p.13
In this suggestion bromine vapors are used. If you have problems to get
this article, let me know your fax number. I then will send a fax copy
--
Gerhard Frank
UNIVERSITAET ERLANGEN-NUERNBERG Phone: +49 9131 85
28606
Institut fuer Werkstoffwissenschaften VII Fax: +49 9131 85 28602
Cauerstr. 6, D-91058 Erlangen, Germany frank@ww.uni.erlangen.de
SEM samples. I am told that removing silver can be a relatively
simple.
The following paper describes a method using "Farmer's"
reducer, a dilute aqueous solution of potassium ferricyanide and
sodium thiosulphate.
"Silver as a removable conductive coating for scanning electron
microscopy" by A.A. Mills Dept. Geology, University of Leicester. UK
Scanning Microscopy, Vol. 2, No. 3 1998 (pages 1265 - 1271)
Best regards
Mike Wombwell
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Regards
Ricardo
www.coleoptera.org