[labnetwork] Use of strontium in sputtering

[Robert M. HAMILTON]

Marc Papakyriakou,

Coincidentally regarding your query, a few days ago the topic of Sr
deposition, an alkali metal, came up in the Marvell NanoLab. I'll share a
few thoughts but first an anecdote.

Many of the alkali metals are pyrophoric and strongly react with air and
water. With water they liberate H2. I began my career as a research
glassblower in a tube lab. Several decades ago, in a clean up of a
microwave tube laboratory, we ran across a Copal jar containing metalic
sodium (Na) covered in kerosene. My senior colleague asked if I had ever
seen what  happened when sodium came in contact with water. He filled a
large stainless lab sink with water and the lump tossed in the sodium -
about the size of an walnut.. It immediately floated (sp. gr. 0.968) and
began melting into smaller and smaller droplets, hissing as they spread out
over the surface of the water. Each droplet glowed and was surrounded by a
the aura of a white cloud. Given the generation of H2 an unanticipated
explosion resulted blowing the water in the sink, as well as Na droplets,
up onto the ceiling. This came down as a shower of water and some reaming
droplets of Na. Fortunately, no one was hurt; everyone was surprised.

Thus, a graphic demonstration of a alkali metal reacting with water. An
artifact of the event was all of the small holes burned into the fabric of
our clothes from the hot Na droplets. I lost a good shirt that day.

Na, along with Ba, Ca, Sr and other alkali metals are routinely used as
cathodes and photo-cathodes. The technical issue is how to deposit them in
such a way the films not react destroying their properties. Air, Oxygen and
water vapor will react upon contact. In the case of creating triple-oxide
electron tube cathodes we wanted the oxide; however, the oxides quickly and
irreversibly hydrate in the presence of the moisture of air destroying low
electron work functions.

When having to do repair work on cathode assemblies that had been formed we
tried a method of using a battery pack to keep the cathodes above 250 C
thus preventing oxidation and hydration with some success. In creating
photocathodes for photomultipliers we resorted to "dispensers", i.e. an
evaporation source that is stable in air and evaporable in situ, under
vacuum.

SAES Getters Inc. offers dispenser-sources such as cessium (I note Sr is
not listed. SAES may do custom work  or have experience with Sr .

The big question is how do our labs safely handle more and more of the
periodic table and how do researches use classic deposition tools to
produce reactive films that are retrievable and workable.

The safety end of this equation is likely the easiest to solve.

Regards,
Bob Hamilton



Robert Hamilton
University of CA, Berkeley
Marvell NanoLab Equipment Manager
Rm 520 Sutardja Dai Hall, MC 1754
Berkeley, CA 94720
Phone 510-809-8618 (desk - preferred)
Mobile 510-325-7557 (my personal mobile)
E-mail preferred: bob at eecs.berkeley.edu
http://nanolab.berkeley.edu/


On Fri, Feb 27, 2015 at 6:27 AM, Papakyriakou, Marc R <
mpapakyriakou at gatech.edu> wrote:

> Dear MTL lab network,
>
> I am a graduate student at Georgia tech and I have a question about
> possible use of strontium in a cleanroom environment. I am working to get
> strontium qualified as a material for use in Georgia Tech's cleanroom, but
> they want to know what handling procedures other cleanrooms use for dealing
> for strontium before they agree to let it be used. I am specifically trying
> to sputter pure strontium. Does anyone in this network have experience with
> using it in this way? And if not specifically strontium, is there a general
> handling procedure for use of highly reactive and/or pyrophoric materials?
>
> Thank you,
>
> Marc Papakyriakou
> Graduate Research Assistant
> Woodruff School of Mechanical Engineering
> Georgia Institute of Technology
> http://www.yeelab.gatech.edu​
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> labnetwork mailing list
> labnetwork at mtl.mit.edu
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>
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