LEED

Sample characterization using Low Energy Electron Diffraction

1. Check that both LEED cables are connected, and make sure that LEED has been degassed.

2. Make sure that LEED is retracted and there is nothing in the way, then move sample to a saved LEED position (if available). Insert LEED while looking inside the chamber.

DANGER: For manual approach use the following order: first move polar angle, then move the LEED forward towards the sample, then move the y axis and finally adjust x and z. For the best focus sample should be as close as possible to the LEED.

Be careful when performing any movement: you can seriously damage the LEED if manipulator touches the instrument. Always look inside the chamber while moving! Be also very careful after you finish the LEED measurement: before performing any rotation move the y axis to 0 and retract the LEED.

Do NOT move LEED with opened shutter!

3. Open the LEED shutter gently, and fix it by turning the screw on the shutter handle.

4. Cover all the windows of the prep chamber with aluminum foil and cover the outer LEED window with a black cap (it has a small hole in the middle for eye or camera, see the picture below). Additionally one can switch off the vacuum gauge in the prep chamber (top AML controller).

5. Switch on the LEED power supply (SPECS). Press down the Cathode knob and rotate clockwise until it clicks. Set cathode current to 2.4 A.

6. Slowly turn the Screen knob to the operating voltage (6 kV).

7. Start Camera (see below). Roughly find sample position. Adjust the offsets of L1 and L2 lenses if needed until you see sharp LEED pattern.

8. Set the desired electron beam energy with Energy knob.

9. When you finish reduce the Screen HV to 0V and reduce the filament current to 0 (until it clicks). Switch off the power switch.

DANGER: Move the y axis to 0, close the LEED shutter, move the LEED backwards, then move the polar angle. Watch all the movements closely!

Using camera to capture LEED images

To view and save LEED images one can use 1. Pylon Viewer or 2. RHEED Igor procedure.

1. Pylon viewer (for fast view, not recommended for data acquisitions)

• Find Pylon Viewer in Start menu (Win button + "Pylon")

• Switch on camera acA1440-73gmNPE (Pay attention that the acA1440-73gm is the electron analyzer camera. If the SES software is running, the Pylon software produce the error message that the camera is used by another application. ) // here goes screenshot of the program with arrows showing the switch-on and camera button

• Use Analog control menu and optimize exposure using Gain to get optimal image quality.

• Press the button with camera to show live view image.

• Press icon with a floppy-disc to save last image to your folder.

//Insert screenshots with camera settings

2. RHEED Igor procedure

• Start new IGOR instance

• Select from the top menu in Igor tab RHEED and open RHEED panel

• In the popup menu select camera name : "Basler acA1440-73gmNPE#..."

• Press the green button to start live image view.

• Adjust camera Gain, Exposure time and Gamma to get optimal intensity and avoid overexposure

• Switch panel to Data Acquisition tab to record the image.

• Press "Record Image" button to start accumulating the signal. When desired statistics is achieve press "Stop recording" to save the image.

• The data are saved as: "root:packages:RHEEDPanel:RHEEDData"

• Modify data name as desired. By default program overwrites the wave if it exists. Keep track on changing the names to not loose the data.

• Save IGOR experiment and export images if needed.