mtang at stanford.edu
Fri Feb 13 16:38:11 PST 2009
Hi Mike --
Good point... (sorry, I had thought 25%, not 1:25)... but I'm actually
more concerned about the bromine. We generally do not approve chemicals
with TWA less than 10 ppm. HBr is at 3 ppm, but we've allowed diluted
solutions and restrictions on how it's used. With bromine at 0.1 ppm
TWA, I'm honestly concerned about using this in a shared facility -- and
in a bench that does not qualify as a fume hood. And there's the storage...
You know, a labmember vomited on the lab floor yesterday -- despite
quick response on cleanup (hooray for Jeannie and George), it was
remarkable how persistent the smell was for some time afterwards
throughout the lab. And how it traveled out into the adjacent hall. It
gave me good appreciation for how well the air gets recycled -- and how
we have to be careful about chemical handling (although if the labmember
had the courtesy to vomit behind the red line on a wet bench...)
Any chance of a proper fume hood elsewhere on campus or in a real
Mike Wiemer wrote:
> 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
> i. above 10% “caution” must be used
> ii. 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 control.)
> 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 <mailto:mtang at stanford.edu>
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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