Proper venting of the evaporation chamber is crucial to maintaining its pristine quality and capability of producing reliable results. Nitrogen as an inert gas will be used as the venting material of choice through much of this process. This Instructable will detail the necessary procedure to properly vent the vacuum chamber, which typically takes around 3.5 hours.
Step 1: Before You Start:
Make sure that all filaments (evaporators, ion gauge, ion pump) have been off for an extended period of time (at least half a day). Neglecting this can damage filament using components, and discontinue the ability of the chamber to reach high vacuum.
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Step 2: Thing(s) You'll Need:
Liquid Nitrogen (you can find this in the BSB at the chemical and lab equipment shop on the first floor E wing) contained within a dewar (metal canister used to transport materials requiring insulation)
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Step 3: Closing the Pump Valves
Isolate the chamber from vacuum pumps themselves by rotating them clockwise all the way. This will ensure no contamination results from back-suction of the pump station oils.
Step 4: Venting the Pumps
With the pumps isolated from the chamber, it is time to vent the pumps themselves. Each pump should be handled separately, in such a way:
1)Attach Nitrogen gas line to intake valve of pump
2)Turn on Nitrogen gas line so that Nitrogen gas is flowing (you need not blast the intake valve, adjust the amount of Nitrogen gas flowing so that the gas stream is audible, but not too much to where the gas line disconnects itself)
3)Power off the pumping station by pressing the power button on the interface control
4)Once pump station is completely powered down, detach the Nitrogen gas line and do the same for the other pumping station
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Step 5: Venting the Chamber
With the pumping stations vented, your attention can be brought to venting the chamber itself. This is the longest step of the process (usually about 3 hours), but much of this time can be spent on other things while you monitor the progress. Venting must be done in the following order:
1)Insert liquid Nitrogen line into liquid Nitrogen dewar, making sure the tip is fully submerged.
2)While in a position where you can clearly hear noises inside the dewar (DO NOT put any part of your body into the dewar itself. Liquid Nitrogen is COLD, and may cause harm if your body is exposed to it). Slowly open (rotate counterclockwise) the Nitrogen intake valve until you hear a "gasp" or light "clink" indicating the chamber has begun taking up Nitrogen.
3)Adjust the Nitrogen valve so that the "gasps" come every second or so. Faster than this may cause contamination of the chamber, and slower than this would take forever.
4)Once the valve is adjusted, it should take around three hours for the chamber pressure to equal atmosphere. During this time, monitor the frequency of the "gasps" every 30 minutes or so to keep the sounds at around 1 every second. You can do other things like homework or watching videos during this step.
5)After the necessary time has passed, the chamber's pressure will be equal to atmosphere (a good check for this is that the open-able window should be able to be opened without much force). Take out the liquid Nitrogen line from the dewar (DO NOT break it, as it will be rigid).
Step 6: Resetting the Valves
All components of the vacuum chamber should now be in equilibrium with the atmosphere. You should prep the chamber now for pumping down after whatever maintenance you plan on doing to the chamber. This primarily entails the resetting of chamber valves to accommodate pumping as opposed to venting. For the three valves:
1)Main Turbo Valve: With the Nitrogen gas line flowing, open the valve (rotate counterclockwise all the way). There may be a "kink" that occurs. This is simply the vacuum pocket kept evacuated within the valve itself, which is the reason for flowing Nitrogen gas into the pump intake once more.
2)Mini-Turbo Valve: Same as above.
3)Liquid Nitrogen Valve: Close this valve (rotate clockwise all the way). There is no need for nitrogen to be flowing in this case.