Cleaning for UHV
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Table of contents
Introduction
UHV means ultra-high vacuum, pressures on the order of 10-10 Torr and less. In order to have such good vacuum considerable care must be taken in both the design/fabrication or parts that go into the vacuum chamber, as well as cleaning these items so they do not become a source of semi-volatile material that migrates throughout the vacuum system outgassing and condensing on surface (like samples for surface physics) forever.
Materials that are suitable for UHV construction have extremely low vapour pressures, like glass, stainless steel, pure titanium, aluminum, copper, solid ceramics sapphire, quartz etc), some bronzes. All of these are materials that will withstand high temperatures without mass loss or alteration.
A few polymers are tolerable if unavoidable: solid teflon (but check specific batches), vespel/kapton.
Some materials that are never permitted in UHV chambers are:
- fingerprints, oils, greases (except Apiezon L and special ultra-low vapour pressure greases made specifically for UHV).
- brass and other alloys of Zn, Sn.
- cadmium, lead, indium and other volatile metals.
Cleaning for UHV
Small parts (sample holders, screws etc.)
Parts are to be first scrubbed clean in hot water and simple green to remove the worst oils and dust. Use (tooth)brushes and Scotchbrite. Place parts in a suitable beaker, wash with clean acetone, then ultra-sonic bath in fresh acetone for 10-15 minutes. Pour out onto Kimwipes to soak up solvent. Repeat with fresh acetone at least once more.
Do not let acetone residue dry; immediately rinse with ethanol or isopropanol. Pour out onto Kimwipes to soak up solvent. Repeat!
In fresh clean alcohol, ultra-sonic bath for 10-15 minutes. Pour out on Kimwipes are repeat at least two times.
Pour out onto Kimwipes to soak up solvent, allow to dry in air on the clean bench in the clean room.
If possible heat to ~120 C or so (much too hot to touch) with a heat gun, and allow to cool, preferably in a pumped desiccator.
Tubing
Plug and fill with acetone, let sit overnight, then rinse with fresh acetone a few times. Push wads of Kimwipe soaked in acetone through till nothing comes out on the paper. Rinse with acetone, then alcohol a few times. Heat with a heat gun while blowing dry nitrogen through.