Re: [Phys-l] Gas Desorption

[Bernard Cleyet <bernardcleyet@redshift.com>]

Joseph!

Not "really":

I aluminized mirrors as an undergrad. * -- while pumping down I used a 
glow discharge don't remember what I cleaned w/ first.  For another 
project I made an optical cell to detect Cl-36 w/ MPT using Brashear 
process.

Research was optical props. (ellipsometry w/ Rochon quartz prisms) of 
several rare earth metals on glass (silica) prisms.  These I cleaned w/ 
chromic acid / H2SO4.  rinsed well w/ chip industry acetone.  I soon 
discovered I had to let "dry" under a beaker on acetone damped kim wipes 
otherwise water condensation and dust.  The monochrometer used same 
silica, so I could use the same dispersion formula.  (~ 0.5 => 5 eV).  I 
then used a W heater while the vac-ion pumped.  [two stage 
sorption-pump].  Not surface science, but some care to have a rather 
clean surface for the metal silica interface **.   I had the boat as 
close as possible to the prism and slide for FECO thickness and 
conductivity.  I opened the shutter when the metal was about half 
evaporated.  I also preheated the "charge" hours first.   I had to 
monitor it, so I was just under a noticeable evap. rate.   The 
conductivity gave one an idea of the purity.  Especially evident w/ Gd 
wherein the phase change was more evident that for any published bulk 
values.

Other cleaning was soon after for a mini-research firm in Santa 
Barbara.  Our unit used an electron gun evaporator to coat Kapton w/ 
carbon.  This was a three person lab.  Boss, friend who did the tensile 
testing and I.  He got values that could only be explained by some 
diamond deposition (bc, very doubting tho).  Later read about diamond 
deposition from, if memory serves, methane.

* Sideline. I was paid for reflectivity in the vacuum UV.  I'm a bit 
hazy, , (1956/7) think I cleaved the salt xtals and quick stuck them in 
the monochrometer and pumped.  The source I remember well - a hydrogen 
discharge using differential pumping, the detector a 1P21/28 coated w/ 
salicylic acid "wave" shifter.

** incident spot ~ 20% of face,  ~ same results on moving the prism about.

bc, whose external examiner was the late (July 6, 2006) Ollie Heavens.


jbellina wrote:

> Depending on beam energy, electrons and ions can modify the surface  
> somewhat...don't know if that would be a concern.  Sulphuric acid  
> tends to leave, as I recall, some adsorbed sulfur which could be a  
> problem.
>
> so, Bernard, are you or were you a surface scientist...what sort of  
> work did you do?
>
> cheers,
>
> joe
>
> Joseph J. Bellina, Jr. Ph.D.
> Professor of Physics
> Saint Mary's College
> Notre Dame, IN 46556
>
> On Nov 25, 2006, at 6:35 PM, Bernard Cleyet wrote:
>
>  
>
> > One may also use electron and ion bombardment and plasma cleaning.  In
> > the case of plasma cleaning it's important to use aluminium  
> > electrode(s)
> > to prevent sputtering.
> >
> > bc, who once cleaned glass using an ancient method (chromic /  
> > sulphuric
> > acid).  Also, substrates w/ electron bombardment and plasma, and just
> > heat w/ a Varian oilless UHV system.
> >
> >
> > http://www.faqs.org/faqs/sci/chem-faq/part4/section-1.html
> >
> >
> > Brian Whatcott wrote:
> >
> >    
> >
> > > At 10:23 PM 11/24/2006, Suraj, you wrote:
> > >
> > >
> > >
> > >      
> > >
> > > > Suyraj Parkash
> > > > 38, Azad Nagar, Jagadhri Road,
> > > > AMBALA CANTT 133006 (India)
> > > > .
> > > > NOVEMBER 25, 2006
> > > > .
> > > > Dear Sirs :
> > > > ..
> > > >            I wish to know the procedure to degas and clean
> > > > vacuum discharge tubes of gaseous impurities specically in
> > > > spectrum analysis gas tubes.
> > > >
> > > >            SurajParkash
> > > >
> > > >
> > > >        
> > > A vacuum bake-out is a good place to start. 150 to 300 degC
> > > Take a look at the easily accessible literature.
> > > As usual, Google is your friend
> > >     <http://www.google.com>
> > >
> > > Take a look at this PDF file for example for an example of
> > > extended gas desorption efforts.
> > > (you need an Adobe reader, which is freely accessible.)
> > >
> > > <http://pubs.acs.org/cgi-bin/abstract.cgi/ancham/1979/51/i08/f-pdf/ 
> > > f_ac50044a029.pdf?sessid=6006l3>
> > >
> > >
> > >
> > >
> > > Brian Whatcott    Altus OK    Eureka!
> > >
> > >
> > > _______________________________________________
> > > Forum for Physics Educators
> > > Phys-l@carnot.physics.buffalo.edu
> > > https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l
> > >
> > >
> > >
> > >
> > >      
> > _______________________________________________
> > Forum for Physics Educators
> > Phys-l@carnot.physics.buffalo.edu
> > https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l
> >    
>
> _______________________________________________
> Forum for Physics Educators
> Phys-l@carnot.physics.buffalo.edu
> https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l
>
>
>