Sounds like the parts of a "salvaged" SEM would be a good start for a
project such as this (assuming the diffusion pump is included - I've been
looking for one for a while but it seems the pumps are almost *always*
missing). But still, if you could find one locally (freight is $$$) there
are a lot of very good, high precision parts just begging to be "hacked".
----- Original Message -----
From: "jimlux" <jim...@earthlink.net>
To: "Discussion of precise time and frequency measurement"
<time-nuts@febo.com>
Sent: Friday, September 03, 2010 12:34 AM
Subject: Re: [time-nuts] Maser info (vacuum levels)
Mark J. Blair wrote:
On Sep 2, 2010, at 10:28 AM, Corby Dawson wrote:
This EFOS maser typically runs with the two vacuum pressures below
1.5 X 10-6 Torr. (as measured via the ion pump current)
Maximum should not exceed about 3.6 X 10-6 Torr for either pump.
The internal vacuum will drop to about 1 X10-7 Torr if the Hydrogen
to the disassociator is turned off.
Back in college, I took a semiconductor device physics course which
included a lab where we made simple ICs (the most complex devices
were SR latches). We had a vapor deposition system for plating on
gold or aluminum, which pumped the chamber down below 10E-12 Torr
maybe 1E-6 micron (1E-9 torr)..
as
I recall, within ten minutes or so after a clueless freshman opened
the beast up and tossed in a bit of aluminum or gold wire and a few
chunks of silicon with their grubby hands (ok, we used tweezers, but
still...). The whole unit was about as big as a refrigerator or two.
It used a rotary-vane roughing pump and an oil diffusion pump with a
liquid nitrogen trap. This was about 25 years ago.
Sounds about right.. the mechanical pump will pull it down to a few
microns in a minute or so (I assume it's like a bell jar with maybe 50
liters total volume?)
Another 10 minues on the diff pump (probably something like a 4" throat..
with a LN2 trap)..
As long as you don't forget to close the High vacuum gate valve before
venting the chamber, very reasonable.
Reading here about the troubles of pulling a very good vacuum, I'm
now wondering what sorts of painful engineering went into making the
machine turn-key and freshman-proof? It's entirely possible that I've
mis-remembered the pressure level, but that's the exponent that stuck
in my mind for whatever reason.
Lots of interlocks to keep you from doing dumb stuff (e.g. venting to
atmosphere with the diff pump hot and connected), actually not all that
dirty.. you probably weren't sticking complex mechanical stuff in there..
basically a wafer that you'd put next to the evaporator source. So no
issues with virtual leaks, etc.
At work, we've got tons (well, tens) of these little evaporation
workstation things.. A rolling cart about a meter by half a meter, and a
meter high, with a bell jar on top. A mechanical two stage pump and a 3"
diff pump under the plate. A couple of feedthroughs for current to heat
the evaporation source. A couple toggle switches, a ion and a
thermocouple gage.. We don't use the for evaporating metal (at least I
and the folks in my section don't)... we use them to test electronics
under vacuum..
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