-- EMK 4/2013

Heavy gallium deposition on the deep-upward looking silicon dopant cell:

+ This is what happens when gallium drips off the water source cooling panel and into the silicon cell:

How to remove gallium from machine-side of system:

• Wrap heater tape in UHV foil to spread heat, prevent fibers from exposure to UHV

• Tape down a thermocouple onto the flange to be heated (use kapton)

• Wrap flange with heater tape and secure with kapton

• place clean foil and a plastic bag under the open port (be careful not to touch port with dirty items!)

• heat up tape, not too slowly. you want to heat locally and not have the entire port get hot. ~55 C is hot enough to remove any gallium residue

• agitate the port to encourage drip (hit on the side with a wrench)

• use tweezers to carefully clean off any gallium accumulation on the knife edge

+ How to remove gallium from the cell:

• This can be done using heater tape or using a nitrogen flow through the purge gas heater

• Place kimwipes in a shallow, wide tub to catch the gallium

• Heat the flange and periodically tip the cell over (careful to not get gallium drip on the cell itself) onto the kimwipe tub to pour out gallium, repeat as needed

• Use clean kimwipes triangles to wick/remove the remaining gallium from the knife-edge

• Use tweezers to remove any balled-up gallium on the cell

Caveats

• the cermanic-metal feedthroughs cannot be etched (will compromise the vacuum), they will need to be replaced

• Pickling solution can be used to remove group-III from stainless steel, but very very carefully. (cannot get it on the filaments or feedthroughs)

• Aqua regia can be used to remove III and V from the alumina insulator tubes

• Remember that whenever Ga is present or suspected to be present, to wrap the component in a layer of kimwipes before wrapping with UHV Al foil. This will prevent unwanted eutectic formation.