Using LEED

Using LEED

1. Check that electron analyzer, X-ray source, evaporators, titanium sublimation pump etc. are off and that all gate valves to other chambers are properly closed.
2. Set the sample position to approximately x = 0 to 5, y = 24, z = 239, Θ = 90°. As x is far from the centre it should be set as the last axis.
3. Check that the knobs of screen, energy and filament are set to zero (completely counterclockwise).
4. Switch on the control unit.
5. Slowly increase filament current up to 1.25 A (I_FIL). The emission should reach at least 0.3 mA (I_E).
6. Increase the high voltage on the screen to 2, 3 or 4 kV.
7. Rotate the energy knob in order to observe spots on the screen.
8. If the spots are too intense even with the screen voltage 2 kV decrease the filament current to 1.1 or 1.0 A.
9. You can use the camera for observing the patterns on the computer display and save them into files using the KolLEED software. The procedure is described on the next page.
10. Check the sample position and the surface homogeneity by scanning the sample surface in the y (horizontal) and z (vertical) directions. Polar angle Θ tilts the sample horizontally; when the beam is perpendicular the [00] spot is behind  the electron gun housing. Vertical tilt can be adjusted only by tilting the sample on the sample holder during mounting.
11. After the acquisition set the energy to zero, switch off the screen voltage, slowly set filament to zero.
12. Switch off the control unit.
13. Move the sample to a safe position. Start with setting x to approximately 25 (centre of the chamber).

Adjustment

• supressor at about one third (black mark on the control unit)
• wehnelt at zero

• energy	L2	L1,3
  0	30	18	adjust with offset
  200	81	463	adjust with gain and repeat