HBr request from John Choi

Mary Tang mtang at snf.stanford.edu
Wed Aug 31 16:58:15 PDT 2005

Hi everyone --

We just had a chat with John Choi about the HBr.  I believe it was 
somewhat approved in yesterday's meeting, but thought we should clarify 
some of the previous concerns that have come up with using this stuff.

1.  Storage:  John will have a 500 ml bottle.  It should not come into 
contact with other oxidizing acids, or Br2 gas will result.  The last 
time this was requested, we had EH&S come and take a look at our 
passthrough and give us the official word.  They said that the 
individual slots (where we allow personal chemicals storage) were 
sufficiently isolated so that we could store what would normally be 
considered chemically incompatible materials in adjacent slots.  The 
risk of spillage mixing was nonexistent.  John has agreed to provide 
additional secondary containment that is enclosed and shatterproof, just 
to be sure that no one inadvertently places another small bottle into 
the same storage slot.  He'll also label the slot.  I think these 
precautions should make the storage of HBr reasonably safe.

2.  Use at the bench:  John will be doing this only at the wbgaas 
station.  The usage there is lower and he can be reasonably assured of 
being the only person working there.  Although he is mixing HB2 with a 
strong oxidizer, he is using a strict protocol whereby there is 
sequential dilution before and after mixing.  He will be providing us 
with this protocol and references, so that we can have it for our records.

This dilute HBr/nitric solution is the only mixture that delivers the 
crystal-dependent etch that he needs.  He has already examined a number 
of other etchants, but not found anything that performs to his 
specifications like this mix.  I think this is sufficient grounds to say 
that he doesn't really have an alternative chemistry that would work for 

In summary, I think John can be trusted to use HBr responsibly.  I think 
we should approve his process (with the caveats listed above).  But I 
also think that we should continue to approve use of HBr acid in the lab 
each time it is brought into the lab.

Does anyone have objections to approval?



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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