Using LEED

WARNINGS:
Do not move the retractor with open shutter.
Do not switch off the power supply without having it shut-down properly before.

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 = 22 to 25, y = 22, z = 244, Θ = 90°.
3. Fully approach the LEED optics using the integrated retractor (rotate the corresponding knob counterclockwise by 64 revolutions without applying any stronger force). It is convenient if your colleague can observe the progress through the perpendicular CF100 viewport.
4. Open the LEED shutter (by rotating the corresponding knob clockwise to 120°, again without any significant force).
5. Switch on the LEED controller in the left experimental rack and confirm the initialization by pressing the BEAM ENERGY CONTROL knob.
6. Switch on the filament by pressing the red FILAMENT ON/OFF button. The current will gradually reach 2.50 A.
7. Let the filament warm up for few minutes. In the meantime you can prepare the camera acquisition:
   • Check that the USB cable is connected to the LEED camera and not to the analyzer viewport camera.
   • Switch all external lamps. Exposing the camera to strong light may damage the CMOS sensor (sensitivity loss)!
   • Switch off the ionization gauge by pressing the Emis. button.
   • (Not necessary: cover the CF160, CF100, CF63 and CF38 viewports with plastic covers).
   • Start the LEED Acquire software..
   • Adjust the sentitivity by Intensity value between 1 and 10.
8. If no or only nA-range BEAM CURRENT appears you can increase the filament current to 2.65 A by pressing the black FILAMENT button and adjusting the value using the BEAM ENERGY CONTROL knob. BEAM CURRENT should be in μA range.
9. Switch on the screen voltage by pressing the red SCREEN ON/OFF button. The voltage will gradually reach 3 kV.
10. Now you can adjust the electron energy by the BEAM ENERGY CONTROL knob to observe the diffraction patterns. If the intensity is too high or too low, slightly decrease or increase the filament current as in point 8.
11. (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.)
    • In order to save each image in the LEED Acquire software select the Folder, fill in properly the fields Sample description, Energy, Screen and Filament, adjust other settings if necessary and click on the SAVE button.
    • After all images are saved EXIT the software in order to be sure that the camera sensor is off.
12. After this you can switch off the screen voltage and filament by both red buttons (optional).
13. Long-press the SHUT DOWN button and switch off the LEED controller.
14. Uncover the viewports, switch on the lamps and the ionization gauge (Emis. button).
15. Close the LEED shutter (by rotating the corresponding knob counterclockwise and locking it with the screw at 15°). At 0° the shutter is not fully covering the optics, see through the CF160 viewport.
16. Fully retract the LEED optics using the integrated retractor (rotate the corresponding knob clockwise by 64 revolutions).

Complete LEED manual is available here .