Dear Colleagues,
in order to implement a FT-RAIRS spectroscopy system on our
present surface science UHV apparatus, we are wondering how to handle
specific
windows materials.
Depending the studies, we would
like to have access to the
following wavenumber regions: 2000-6000cm-1 or 600-6000cm-1. For the
moment we
are thinking about two different windows material, CaF2 for the former
range
and KBr for the later range.
We have some experience with
differentially pumped CaF2
windows which withstand the difference of pressure (UHV/1bar) and the
bake out
of the chamber (@120°C). We think to do the same for KBr windows, i.e.
place
the KBr windows at the interface between UHV/1bar, between two Viton
O-ring
seals and differentially pump the space between, but we will appreciate
some
advice concerning KBr windows.
For KBr, what thickness should we
use for a 50mm diameter
window with a difference of pressure UHV/1bar?
Is there any precaution to take
during the bakeout (KBr
seems to be softer at higher temperature)?
Since we plan to work with an
evacuated spectrometer, we will
have on the outside of the KBr windows a 1mbar pressure, i.e. a
gradient UHV/1mbar/1bar,
the KBr windows being at the interface UHV/1mbar. Should we worry about
changing
the pressure quickly (~1sec) on the KBr windows from 1mbar to 1bar
during
venting the spectrometer?
Furthermore, does anybody have
experience with other
materials, e.g. ZnSe which seems less difficult to handle?
I thank you in advance for your
help.
With my best regards,
Régis
Bisson
--
_______________________________
Dr. Régis Bisson
EPFL - LCPM
Swiss Federal Institute of Technology
Laboratoire Chimie Physique Moléculaire
Station 6
CH-1015 Lausanne, Switzerland
Tel. +41 (0)21 693 3040
Lab. +41 (0)21 693 3124
Fax. +41 (0)21 693 5170
http://lcpm.epfl.ch/bisson.php
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