EPMA Vacuum Technology Discussion

[Probeman]

This is a topic for discussion of general vacuum issues in EPMA, both JEOL and Cameca instruments.

I'll start this thread by mentioning an excellent technology that Cameca provided for my SX100 instrument instead of the usual "cold trap finger" and "oxygen leak jet" hardware for minimizing carbon contamination.

When I actually set out to purchase the instrument about 5 or 6 years ago, the Euro was very unfavorable for the US, and although I had budgeted for a dry pumped turbo system, I could no longer afford it. So instead I suggested to Cameca that they provide a diffusion pumped system, with a cryo-trap over the diffusion pump and without the cold finger and oxygen jet.

The results were excellent as seen in our acceptance testing and the air cooled cryo-unit runs at 100 degrees kelvin! So it not only traps oil, but even water quite efficiently.  About once a year we warm it up to boil off all the contaminants with the secondary valve closed.

The link to the unit is here:

http://www.brooks.com/products/cryopumps-cryochillers/cryochillers/pcc-compact-coolers

The only trouble we've had over the last 6 years is to replace one cooling fan on the compressor. And zero LN2 and oxygen consumption...



Not too bad for an inexpensive and reliable oil pumped vacuum system!

Edit by John: There's another method which JEOL attaches to their airlock (see attached pdf image from Aachen), but I would prefer an "in-situ" cleaning method, so only the area of interest is cleaned as described below in the request for a UV laser for cleaning concurrently with the x-ray acquisition.

[Gseward]

Our SX100 has a turbo pumped system backed with scroll pumps. This test was done when the instrument was being installed. I have no idea what it is like today!

Description : test made on pure copper at 10kV 100nA.



Rate = 0.033% and is a similar result to John Donovan's Aqua Trap system. Not sure where the 'Limit without device' spec is from  - I'd be interested to see experimental results from a diffusion pumped system without any decontamination devices. It would also be interesting to compare numbers from somewhere that does a lot of Carbon analysis (Aachen 8530??).
Have you done a retest lately John? I have a plasma cleaner that I've been meaning to bolt onto the probe, so perhaps it is time to do a new test 'before and after'.

Our vacuum system hardware has been very reliable for 3.5 years. All I've had to do is replace the tip-seals in the scroll pumps a few times and clean the high vac gauge.

gareth

[Probeman]

This is a crazy idea, but I'd like to try a hydrocarbon experiment in my EPMA vacuum system and need to borrow or buy a small UV laser that I can mount just outside the instrument.  The specs my engineer suggests are as follows:

266 nm UV pulse laser (frequency quadrupled YAG), diode pumped solid state (DPSS)

Typically these devices are some 10 to 20 cm long. If anyone has one of these guys that we can borrow or buy (cheaply!) I would be very interested to hear from you.

Thanks.