HowTo&Troubleshooting

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How to perform LEED

1) DANGER: Move the sample in the LEED position in the following order: Move first the angle, then x, then move the LEED forward towards the sample, then move the y, always monitoring the sample holder distance from the CF63 lateral window in front of the gate valve. The final distance of the top screw on the sample hoder should be few mm from the LEED. DANGER: Be careful while moving the y or the LEED or the rotation: you can damage seriously the LEED if the sample holder touches the instrument. Be also very careful after you finish the LEED measurement: before performing any rotation move the y to 20 and retract the LEED. Always use the CAMERA n.3 to monitor the position of the sample holder!

2) Switch on the LEED. Set Operate. Press ON on the filament. Wait until it reaches the operating current.

3) Press ON on the SCREEN Hi Voltage. Wait until it reaches the operating current.

4) If you want to use the remote control for the energy press save/remote.

5) When you finish switch OFF the screen, then switch OFF the filament, then press down the switch off button on the "Setting" panel for 2-3 second until on the screen the message "you can switch off the LEED" appears. Switch off the power switch.

6)DANGER: Move the y to lower values, move the LEED backwards,then move the angle, always monitoring the sample holder distance from the CF63 lateral window in front of the gate valve.


 

Working distance from sample 18 mm

Beam energy: 5 eV to 750 eV

Beam current: 2 μA at 100 eV and 0.5 mm beam size

Beam size from 1 mm to 250 μm - adjusted by Wehnelt potential, limited by exchangeable aperture down to 50 μm

Electron source Tungsten-2% Thoriated filament standard, single crystal

Bakeability Under vacuum, 250 degree C maximum

LEED Degassing Procedure

Before using the LEED, ask the beamline scientist if the instrument was degassed after the last bake out.

Check that the 3 connectors are plugged on the instrument.

To degass the LEED. The pressure in the main chamber has to be in the 10-10 mbar. Ask the beamline scientist for assistance. If you already know the instrument: Set the controller on Programming (Prog.) instead of Operating. Set the filament to 1 A and press on. Wait until it reaches 1 A, then increase the filament by 0.2 A every 5 minutes, until you reach the operating current (2.6A), while the pressure remains below 5x10-9 mbar. Wait for 1-2 hours, until the filamenet is completely degassed.


 

 

Last Updated on Thursday, 13 September 2018 12:57