Exposing the sample with gases

Exposing the sample with gases

1. Check that LEED, electron analyzer, X-ray source, evaporators, titanium sublimation pump etc. are off and that all gate valves to other chambers (also the electropneumatic valve 10 towards the beamline) are properly closed.
2. For the desired exposure in langmuirs (1 L = 10^-6 torr×s) calculate the necessary pressure and time. Reasonable times are between 30 s and 30 min. The pressure must not exceed 1×10^-6 mbar. This limit is dependent on the gas and exposure time, the rule is that the pressure after the exposure should drop within reasonable time. So be careful especially with water, methanol and similar compounds.
3. On the ionization gauge touchscreen tap the current pressure unit (mbar) and change it to torr if needed:
   
4. Start the Pressure Display software if needed. Display the experimental (ioniz.g.) channel.
5. Open slowly the corresponding leak valve. When you reach the desired pressure start the timer.
6. Observe and adjust the leak valve if necessary.
7. When finished close the leak valve without forcing it.
8. Wait for the pressure in the chamber to recover. The analyzer and the X-ray source cannot be operated before the cold-cathode pressure reading is below 5×10^-8 mbar due to interlocks.
9. Set the ionization gauge controller units back to mbars if needed.

Installing gas bottles (CO, O2, H2...) Close the valve on the bottle and disconnect the bottle. Connect the new bottle with the desired gas. Connect the small turbopumping station to the Swagelok pumping valve. Close the manual venting valve on the turbopump. Start the turbopump. The complete manual of the controller is here. Main parameters are: 002 Standby slow speed operation in order to protect the turbopump from overload 309 ActualSpd actual rotation frequency; it should be 1000 Hz 340 Pressure pressure reading from the Pirani gauge on the pumped line Open the Swagelok valve and wait until the read pressure is low. Close the Swagelok valve. Open the valve on the bottle. Close the valve on the bottle. Repeat steps 6-9 at least three times. After the last cycle leave the valve on the bottle open. Switch the turbopump off and wait until the it slows down below 500 Hz. Open slowly the manual venting valve on the turbopump until the rotation stops.

Installing liquids (H2O, CH3OH...) Disconnect the quartz glass flask, empty it and clean it (CF16 port). Fill it with about 1 cm level of the desired liquid and connect it back (with new CF16 copper gasket). Connect the small turbopumping station to the Swagelok pumping valve. Close the manual venting valve on the turbopump. Start the turbopump. The complete manual of the controller is here. Main parameters are: 002 Standby slow speed operation in order to protect the turbopump from overload 309 ActualSpd actual rotation frequency; it should be 1000 Hz 340 Pressure pressure reading from the Pirani gauge on the pumped line Freeze the liquid with LN2. Open the Swagelok valve and wait until the read pressure is low or until the ice starts to thaw. Close the Swagelok valve. Leave the liquid thaw completely.. Repeat steps 6-9 at least three times. Switch the turbopump off and wait until it slows down below 500 Hz. Open slowly the manual venting valve on the turbopump until the rotation stops. Note: In order to avoid the cross-contamination of vapours it might be useful to install, pump and bake out the empty glass flask before putting new liquid.

Quadrupole mass spectrometer

The QMS is used for checking the residual gas composition, possible leaks and purity of the gases. The software Quadstar is described here.

1. Check that the pressure is below 1×10^-6 mbar.
2. Connect the QMS power supply to electric network. Two green LEDs will light on the QMS electronics.
3. Open the Quadstar Measure software:
   
4. Switch on the Emission and multiplier (SEM) voltage in the Setup - SEM/Emission Control menu:
   
5. Start the Analog scan - SCAC.SAP in the Scan menu:
   
6. Adjust the parameters using Parameters - Setup and Parameters - Channel menu (mass range, intensity range):
   
   
7. Observe the spectrum and save it using the File - Save cycle data into a .sac file if needed:
   
8. Close the scan window.
9. Switch off the Emission and multiplier (SEM) voltage in the Setup - SEM/Emission Control menu:
   
10. Close Quadstar Measure.
11. Disconnect the QMS power supply from electricity.


12. If you saved the data into .sac file use the Quadstar Dispsav software to Open, display the data and Convert them to ASCII (.asc) files that can be imported into common spreadsheet software like Excel, Origin or Igor for further processing.