5/29/97
hopefully start a
Ph.D. in Archaeology (a long way from Marine Zool. and EM!) but
before I go
I've got to do an animated sequence from the SEM, in stereo, on a
very
small spider (a couple of thousand frames). Should look good.
The folks
here said I should pass on the mounting technique, so here it is.
Tip #1: BSE detection and Carbon
I'm shooting with a Robinson BSE detector. It gives a more
"real"
illumination than SE and has the benefit of not "seeing" carbon.
The
specimen is normally mounted on top of a minuten (entomological)
pin which
is clamped in a 12mm "vice-stub" and tilted at 90 degrees in the
SEM. On
my Cambridge S120, the top of the stage mechanism is now out of
view but
you still see the bottom plate below. I've covered that with a
piece of
alfoil which has been painted with thinned-out carbon dag, making
it a
perfectly black, "studio-shot" background when using BSE.
Tip #2: No unsightly props
Further, instead of mounting the specimen on the usual minuten
pin, I've
fixed it to the end of the lead from a clutch pencil
(draughtsman's
pencil), so the pin is also virtually invisible under BSE.
Doesn't the
pencil lead get coated too? I've taken a medium-bore tip from a
syringe,
held it in an alligator clip, and fed the pencil lead down into
it leaving
just the specimen exposed for coating.
Tip #3: Accuracy in mounting
Mounting very small specimens on a pin-tip is difficult at the
best of
times. As the animation sequence is to be in stereo, the
specimen must be
at exactly the right angles to the pin and we don't want to see
any
excessive blobs of dag. You'll need a small bench vice,
micrometer screw
guage and double sided tape (DST). Lay your stereomicroscope
down on its
front with the head reversed so that the eyepieces point up and
the light
path is (roughly) horizontal. Clamp the side of the screw guage
into the
side of the vice and place it in front of the 'scope. Secure your
specimen
to a foam block with crossed minuten pins and secure the block in
position
to the opposing pole of the screw guage with DST. Fix the
mounting pin to
the mobile shaft of the screw guage with DST. Watching it all
through the
'scope, do a dummy run to ensure that everything lines up. Screw
the pin
up, apply a meniscus of dag to the end of the pin and screw it
down to the
specimen. Leave to dry.
Tip #4: Centre of rotation
Because this sequence includes rotating the animal 360 degrees,
the pin has
to be at the centre of rotation of the stage. However, in my
12mm
"vice-stub", the vice is offset. Instead, I'm using a pop-rivet.
Push the
nail out and use the rivet and its collar; the rivet has the same
diameter
as the shaft on a normal 12mm grooved stub. Put the pin down the
bore and
dag it into a central position.
Hope you find these tips helpful and if you're in Oz around
September, drop
into the Australian Museum, Sydney, to see the stereo animation
sequence of
the spider (unfortunately, I'll be gone by then).
Geoff Avern
Manager
Microscopy Labs
Australian Museum
Sydney, Australia