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Venting, bake-out and degassing

Venting the analysis chamber

The analysis chamber can be open only during the shutdown period to insert evaporators needed for the following Run and/or to repair the equipment, as the total time of the whole operation including bake-out and degassing is at least 5 days.

For pumping and pressure reading in the analysis chamber we refer to this page. To vent the chamber:
  1. Switch off all devices in the analysis chamber - gauges (ionization and two cold-cathode), evaporators, sample annealing, X-ray source, electron analyzer, ion gun, LEED, titanium sublimation pump etc. Let the ionization gauge flange cool down.
  2. Check that the following gate valves are closed:
    • towards the refocussing mirror chamber of the beamline (electropneumatic valve 10),
    • towards the preparation chamber - bottom.
  3. Connect the nitrogen gas line to the venting valve of the big turbopump. Open partially the Swagelok valve to let nitrogen flow.
  4. Close the valve between the rotary vane pump and the sample manipulators. (For longer periods you can also switch the rotary pump off and immediately vent it by disconecting any KF flange.)
  5. Close the roughing valve between the big turbopump and the scroll pump. (For longer periods you can also switch the scroll pump off by disconnecting the plug.)
  6. Switch off the big turbopump and wait until it slows down below 100 Hz.
  7. Open the venting valve on the DCU controller (by enabling automatic venting by setting parameter 012 on the controller to 1) and check that the pressures in the neighbouring chambers do not increase.
  8. Wait until the chamber is fully vented (~30 min depending on how much you open the nitrogen valve). Bellows of the manipulator and the X-ray source retractor become soft when done.
  9. Close the nitrogen valve.
  10. Close the venting valve on the DCU controller (by disabling automatic venting by setting parameter 012 on the controller to 0).


After this you can open the selected ports, fix the necessary things, close properly all ports and start the pumps as following:
  1. Switch on the rotary vane pump of the manipulator (if off in step 4 above) and open the pumping valve of the manipulators.
  2. Switch on the scoll pump (if off in step 5 above) and slowly open the roughing valve below the big turbopump.
  3. Switch on the big turbopump and wait until it reaches 820 Hz (it can take up to 10-20 min).
  4. Switch on both cold-cathode gauges in the analysis chamber.
  5. When the displayed pressure is lower than 10-4 mbar switch on the ionization gauge.

Venting the preparation chamber

The preparation chamber (- bottom or both - bottom and - top) is vented if some custom equipment (usually evaporators) is to be installed there. The total time of the whole operation including bake-out and degassing can be as short as 12 hours so it can be performed overnight even during the experimental Run.

For pumping and pressure reading in the preparaion chamber - bottom we refer to this page and for the preparation chamber - top to this page. The venting sequence is:
  1. Switch off all the equipment in the preparation chamber(s) - cold-cathode gauge, evaporators, sample annealing, ion gun, titanium sublimation pump etc. Only the full-range gauge in the top part can stay on.
  2. Check that the following valves are closed:
    • gate valve towards the analysis chamber,
    • gate valve towards the load lock,
    • gate valve between the preparation chamber - bottom and the preparation chamber - top (if you do not vent the top part),
    • gate valve between the preparation chamber - top and the UHV part of the electrochemical cell (if you do vent the top part),
    • angle valve between the preparation chamber - top and the load lock (if you do vent the top part).
  3. Connect the nitrogen gas line to the venting valve of the turbopump of the preparation chamber - bottom. Open partially the Swagelok valve to let nitrogen flow.
  4. Switch off the turbopump of the preparation chamber - bottom. The venting valve will automatically open at 500 Hz.
  5. Wait until the chamber(s) is(are) fully vented (~15 min depending on how much you open the nitrogen valve). Bellows of the manipulator becomes soft when done.
  6. Close the nitrogen valve.


After this you can open the selected ports, fix the necessary things, close properly all ports and start the pumps as following:
  1. Switch on the turbopump of the preparation chamber - bottom.
  2. Wait until the turbopump reaches 1000 Hz (it can take up to 10-20 min).
  3. Switch on the cold-cathode gauge of the preparation chamber - bottom.


Now you can start preparing the bake-out, as described on the next page.


Bake-out of the analysis chamber

  1. Disconnect all cables and water-cooling tubes from the equipment on the analysis chamber except for the turbopump, the titanium sublimation pump and gauges. Write down which cable was connected where. Usually (from top to bottom):
    • sample manipulator (thermocouple connector, 2 heating connectors, 4 z- and Θ-control unit cables, Θ-motor connector, grounding banana plug),
    • quadrupole mass spectrometer (2 connectors),
    • sputter ion gun (1 connector),
    • LEED (2 connectors+grounding on the flange10 and 2 on the CCD camera),
    • evaporators (2 grounding cables on the CF63 viewport13, all filaments, high voltages, thermocouples, water cooling tubes12-15; then blow out the residual cooling water using compressed air),
    • X-ray source (2 water tubes of the head cooling circuit, then disconnect the cover interlock connector, remove the protective cover fixed with 3+3 screws2+4, inside disconnect 2 water tubes of the anode cooling circuit and a high voltage banana plug; filament connector outside with the feedthrough1.5 to be covered with a small protective cap; blow out the residual cooling water using compressed air),
    • electron analyzer (detector box data connector, 2 high voltage connectors, lens connector).
  2. Completely remove all other components that should not be baked-out, typically:
    • sample manipulator Θ-controller (2 screws13), Θ-motor (4 screws3), LN2 cooling inlet tank and outlet bottle13-15,
    • quadrupole mass spectrometer (the whole white electronics unit, 2 screws4),
    • sputter ion gun fan (tied with a wire),
    • LEED covering sheet, its holder and camera holder with camera (4 nuts13),
    • lights on viewports,
    • electron analyzer detector electronics (2 clips).
  3. Place the thermocouples to the following positions (or check them if already there):
    • manipulator bellows (1),
    • analysis chamber (2),
    • electron analyzer detector flange (3),
    • pumping section at the bottom of the chamber (4).
    The thermocouples should have a thermal contact but not the electric contact with the chamber, otherwise the bake-out controller will not work properly.
  4. Cover the bellows on the manipulator with a single layer of aluminum foil and wind a 3 m-long heating tape starting from the CF160 flange passing around the xy stage, Θ rotary feedthrough, z bellows up to the feedthroughs at the top.
  5. Cover sensitive areas (viewports, bellows, feedthroughs, leak valves, X-ray source ceramic insulator) with aluminum foil.
  6. Place one or two heating tapes where missing (evaporators, X-ray source).
  7. Cover the whole chamber including all bakeable parts with several layers of aluminum foil. Be careful that the cables that remain connected (gauges and pumps) stay outside. The bellows on the manipulator usually requires more layers otherwise it might not reach the desired temperature.
  8. Check that heating tapes contacts are not grounded to the chamber and connect them to the socket box of the bake-out controller using extension cables. Use (as in step 3):
    • channel 1 for the manipulator (1 tape),
    • channel 2 for the chamber (5 tapes + those added in step 6),
    • channel 3 for the electron analyzer (4 tapes),
    • channel 4 for the pumping section (2 tapes).
  9. Connect the socket box to the electric line and to the bake-out controller unit (grey cable).
  10. Connect the thermocouples to the bake-out controller unit and switch it on. Set the program to temperatures 130 °C for the channels 1 to 4. The total time should be at least 36 hours (usually 40-48; it is convenient if it finishes early morning, so the chamber cools down a bit before you arrive to work).
  11. If the pressure is in low 10-6 mbar order and the water cooling of the turbopump is on you can switch on the bake-out on the bake-out controller.
  12. Switch on the heating jacket on the turbopump (parameter 001 on the control unit).
  13. Check regularly temperatures and pressure, at least in the first hours after the start, until 130 °C is reached. To monitor the pressure trend you can use the Pressure Watcher software.
  14. When the bakeout is finished switch off the heating jacket on the turbopump (parameter 001 on the control unit).
  15. Degas the titanium sublimation pump using the corresponding controller (25 A for 15 min).
  16. Remove aluminum foil, heating tapes and thermocouple (4) that you added in steps 3-7.
  17. Install and connect back all parts removed in steps 1-2.

Bake-out of the preparation chamber (and load lock, if needed)

  1. Disconnect all cables and water-cooling tubes from the equipment on the preparation chamber - bottom (and eventually preparation chamber - top and/or load lock) except for the turbopump, the titanium sublimation pump and gauges. Usually (from top to bottom):
    • sample manipulator (thermocouple connector, 2 heating connectors) if applicable,
    • quartz crystal microbalance (1 connector, 2 water tubes13-14; then blow out water from the cooling tubes using compressed air),
    • sputter ion gun (1 connector),
    • lights on viewports,
    • evaporators (if applicable).
  2. Place 2-4 thermocouples in different heating zones (including the manipulator bellows if applicable). The thermocouples should have a thermal contact but not the electric contact with the chamber, otherwise the bake-out controller will not work properly.
  3. Cover the bellows of the manipulator with a single layer of aluminum foil and wind a 3 m-long heating tape starting from the CF160 flange passing around the xy stage, Θ rotary feedthrough, z bellows up to the feedthroughs at the top (if applicable).
  4. Cover sensitive areas (viewports, bellows, feedthroughs, leak valves) with aluminum foil.
  5. Place other heating tapes where missing (evaporators, transfer rod if applicable).
  6. Cover the whole chamber(s) including all bakeable parts with several layers of aluminum foil. Be careful that the cables that remain connected (gauges and pumps) stay outside. The load lock door and both full-range gauges (if applicable) should be covered less than the all-metal parts in order to lower the temperature.
  7. Check that heating tapes contacts are not grounded to the chamber and connect them to the socket box of the bake-out controller using extension cables. Use the heating channels consistently with the thermocouples (see step 2).
  8. Connect the socket box to the electric line and to the bake-out controller unit (grey cable).
  9. Connect the thermocouples to the bake-out controller unit and switch it on. Set the program to the temperatures 100-130 °C. The total time should be at least 12 hours depending on the desired final pressure. It is convenient if it finishes early morning, so the chamber cools down a bit before you arrive to work.
  10. If the pressure is in low 10-6 mbar order switch on the bake-out on the bake-out controller.
  11. Switch on the heating jacket on the turbopump of the preparation chamber - bottom (and load lock if applicable) - parameter 001 on the control unit.
  12. Check regularly temperatures and pressure(s), at least in the first hours after the start, until the set temperatures are reached.
  13. When the bakeout is finished switch off the heating jacket(s) started in step 11.
  14. Degas the titanium sublimation pump using the corresponding controller (25 A for 15 min).
  15. Remove the aluminum foil, heating tapes and thermocouples added in steps 2-6.
  16. Install and connect back all parts removed in step 1.

Some equipment in the vented chambers must be properly degassed before use, as described on the next page.




Degassing

Some equipment must be properly degassed before use. It can be done at any time but it is convenient to do it until the chamber is still warm after the bake-out, so the degassed molecules adsorb less on other surfaces. Only the electron analyzer detector must be degassed after everything cools completely down!

The typical degas procedure consists of step-wise reaching the operating parameters while observing that the pressure does not rise much.

Titanium sublimation pump

The degas procedure is fully automated by the corresponding controller (degas knob) and consists of slow reaching 25 A filament current and keeping it for 15 min. It is enough to degas one filament. Nevertheless, the pressure significantly rises during every successive sublimation cycle (38.5 A, 1 min) up to 10-8-10-7 mbar. Observe the pressure during first several sublimation cycles after the bake-out and abort the sublimation if the pressure is too high..
Estimated time: 30 min.


Quadrupole mass spectrometer

No special degas procedure is required. Switch on the filament as described here and keep it on for about 30 min. You can also record the mass spectrum. If there is no leak in the chamber the intensity of mass 14 should be lower than that of mass 15.
Estimated time: 30 min


Sputter ion gun

The corresponding power supply provides an automated degas procedure activated by the DEGAS knob. It is enough to degas one filament.
For details see the corresponding manual.
Estimated time: 10 min.


LEED

The filament is degassed by setting WEHNELT to zero and then slowly increasing the FILAMENT current (IFIL) up to 1.25 A and waiting until the emission current IE reaches 0.5 mA.
For details see the corresponding manual.
Estimated time: 3 hours.


Knudsen-cell evaporators

The evaporators are degassed on first use by reaching the desired parameters.
Estimated time: 30 min.

X-ray source

The power supply provides semi-automated procedures for:
  1. conditioning of both filaments (by ramping the filament current; one at a time),
  2. high-voltage conditioning of both anodes (by ramping the high voltage; both at the same time), and
  3. power conditioning of both anodes (by ramping the emission current, one at a time). 
For details see the corresponding manual.
Estimated time: 15 hours.



Tectra e-beam evaporators

  1. If the filament is new it must be conditioned as described in the manual.
  2. Keep water cooling closed.
  3. With high voltage off slowly reach the filament current 6 A while observing the pressure.
  4. WIth high voltage on slowly reach the desired emission and wait until the temperature of the evaporator (read by an internal thermocouple) reaches 150-200 °C.
  5. Switch off the emission, filament limit and high voltage and wait until the temperature decreases below 100 °C.
  6. Open water cooling.
  7. With high voltage on slowly reach the desired emission and keep it on for several minutes.
  8. Switch off the emission, filament limit and high voltage.
  9. After several minutes close water cooling.
Estimated time: 2 hours.

Oxford e-beam evaporator

  1. Connect the desired pocket as described here.
  2. If the filament is new it must be conditioned as described in the manual.
  3. Open water cooling.
  4. With high voltage off slowly reach the filament current 6 A while observing the pressure.
  5. WIth high voltage on slowly reach the desired emission and keep it on for several minutes.
  6. Switch off the emission, filament limit and high voltage.
  7. Repeat for other pockets if needed.
  8. After several minutes close water cooling.
Estimated time: 2 hours.



Sample manipulator and sample

The degas happens at first several cycles of sample annealing.
Estimated time: 30 min.




Electron analyzer detector

Warning: this is the only degas procedure that must be done after complete cooling down. Wait at least 72 hours after the bake-out finish!

The detector is degassed by slowly increasing the voltage from 0 up to ~2000 V with all excitation sources off. It is done by using the detector voltage scan saved in the yymmdd_start-up.xml file in the current dara folder (D:\Data\2020\). For parameters you can use any recent file.
For details see the corresponding manual.
Estimated time: 30 min.


Last Updated on Friday, 12 March 2021 10:10