Specmat Request

Mike Wiemer mwiemer at sj-solar.com
Fri Feb 13 15:57:02 PST 2009

P.S. - One more thing.


If you look at Figure 1 in that paper, you will see that for 10% Br, the
solution heats up to only 28C in a controlled manner. Our suggested 4%
will heat up even less. It is Figure 2 you want to avoid which is for







From: Mike Wiemer 
Sent: Friday, February 13, 2009 3:50 PM
To: 'Mary Tang'
Cc: Ed Myers; mtang at snf.stanford.edu; Michael Sheldon;
specmat at snf.stanford.edu
Subject: RE: Specmat Request


Hi Mary & Specmat,


Wow! I never cease to be surprised by your thoroughness (interesting
find on that paper).


I would like to point out a couple of things:

1.)    The concentration of Br will be ~4% (1:25). 

a.       This is well below the 10% value stated in the document 

above 10% "caution" must be used

Between 20%-25% "hazard increases"

b.      See the highlighted sentence in the attached document on the
last page

2.)    The vessel we are going to use is 12" in diameter, and 4" high
(with a pour mouth)

a.       This reduces the beaker-breaking explosion hazard


As always, I defer to your decision, but I know this can be done safely,
provided we have the proper space to do it in. 








From: Mary Tang [mailto:mtang at stanford.edu] 
Sent: Friday, February 13, 2009 11:44 AM
To: Mike Wiemer
Cc: Ed Myers; mtang at snf.stanford.edu; Michael Sheldon;
specmat at snf.stanford.edu
Subject: Re: Specmat Request


Hi Mikes --

Actually, we have never (as far as I know) approved liquid bromine in
the lab.  The TWA exposure limit on this is 0.1 ppm.  Compare to
chlorobenzene which is 10 ppm.  Or HBr, which is 3 ppm.

We've approved HBr solutions as you describe and, in fact, have some
detailed protocols for this.  But I don't believe I've ever seen Br2 in
our lab.  I understand it's commonly used as an etchant for certain
semiconductor films.   But also have heard some horror stories.  I think
just about any of the old-time GaAs researchers will have bromine story.
See the attached.  We did approve dilute HBr solutions for use at the
wbgaas station with alcohols, but under very specific conditions
(controlled pH, which I understand is key to keeping things under

I am honestly not sure we could accommodate handling of liquid bromine
-- not unless we can come up with a really safe way of doing this.  My
feeling is that this should be done in a proper fume hood (with
explosion sashes and indescructible/inflammable work surfaces), not the
wet benches we have at SNF.

But I tend to be conservative on chemical handling.  Other SpecMat'ers
-- especially those with more experience with this -- what do you think?


Mike Wiemer wrote: 

Hi Ed & Mary, 


Here is a Specmat Request document on Bromine/Methanol etching we want
to do at the WBGaAs bench. 


Ed and I spoke about this over the phone. It seems this is an "already
approved" chemical in the lab, however, we decided we needed to submit a
use/procedure request (see attached). 


Please let me know when we have the green light, or if there are
additional issues we need to address. 






Mary X. Tang, Ph.D.
Stanford Nanofabrication Facility
CIS Room 136, Mail Code 4070
Stanford, CA  94305
mtang at stanford.edu
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