SPI Supplies Scintillators for SEM
Bakeout information for UHV applications
With the growing number of SEMs, Auger systems, electron probe
microanalyzers that operate under UHV conditions, we are being
asked questions we never used to get asked as recently as just
a few years ago. But there is enormous interest about information
on the UHV compatibility of the scintillators and also, how the
scintillator would actually perform during a bakeout.
We will discuss the two classes of scintillators separately, first
the conventional P47 powder scintillator and after that, the single
crystal scintillators, YAG and YAP.
P47 Powder Scintillators:
This is a three part system, made up of the glass substrate, the
P47 phosphor and a proprietary polymeric binder for bonding the
phosphor powder to the glass surface. The polymer itself can be
baked out as high as 400°C.
YAG and YAP:
Certainly both YAG and YAP can indeed be baked out, and we also know that
even at 400°C, we can not detect any change in the doping of the Ce+++
within the single crystal. However, for most SEM applications, at least,
these single crystals are aluminum coated and once one takes the
scintillator above 100°C , in most environments, at least, the
aluminum layer starts to oxidize. Hence we do not recommend baking
at higher temperatures unless you can be absolutely certain that
there is complete absence of oxygen. Otherwise the aluminum coating
will be oxidized, the now oxidized coating will have to be removed
and a new one applied (by vacuum evaporation).
We hope this information about bake out will be useful. This is
obviously a somewhat arcane kind of discussion and our data base
of experience is limited.
We would welcome any further feedback
from anyone who has had other experiences or has other information
that might be of interest to the user community at large.
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Saturday October 11, 2008
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