Microscope alignment

Routine Alignment

  1. Make sure that the surface is in focus @ Obj. current of 1520 mA. The microscope settings are optinized for this very focus.
  2. Toggle TL, find its center of motion and mark it on the screen.
  3. Set the sample tilt so that the axis of the objective lens overlaps with that of TL.
  4. Align FL, IL and P1. You may insert the small field limiting aperture, which makes this a lot easier in LEEM.
  5. Don't align analyzer RL, keep the values you find.
  6. Align ACC lens, using SEL and Acc lens Align 1,2.
  7. Align P2, P3.
  8. Check that the Inner Lens and Acc Lens are in focus.
  9. Optimze the imaging conditions using Obj. Stig. A,B.
  10. Re-check that the Inner Lens and Acc Lens are in focus. Setting these lenses properly is key to achieve the best imaging conditions and homogeneity of lateral resolution.
  11. Iterate if necessary

LEED optimization

LEED is not sufficiently sensitive to set the alignment of the lenses correctly, therefore, the electron-optical system should be aligned only in imaging mode. However, LEED may help you to find the right value of Ret. Lens Aligners and SEL, resulting in a perfectly symmetric diffraction pattern.

First alignment

After a bake out or major maintenance, it is necessary to align the microscope from scratch. To do this, you need to use the Elmitec patterned SiO2 sample or a thin film grown on W(110).

  1. Align with PEEM at Vst = 0 V, field of view of at least 50 um. Start the mercury lamp and maximize intensity on the detector
  2. For our system, SELO/SELI = 1.95 fixed. This ratio ensures that a square object is imaged as a square. It can be verified using the Elmitec patterned SiO2 sample. Try to work at objective focus of 1520 mA (HV@16 kV) or 11612 mA (HV@18kV). Keep TL at 608 mA (HV@16kV) or 643 mA (HV@18kV), which ensures maximum throughput at the contrast aperture.
  3. In order to take advantage of the double focusing properties of the separator at an angle of 60°, Im EQ X,Y = 0. Field Lens Align X;Y should be also as close as possible to 0. To realize this condition, toggle TL, in order to identify the optical axis of the lens. Impose Field Lens Align X = 0. Then, align FL, using only Field Lens Align Y and SEL0/SELI in combination. The procedure is iterative and you will need to repeat it a couple of times at least. Use a recognizable object (an island) to do this. Use one of the markers to mark the TL/FL axis. Note that the object might need to be moved using the X,Y manipulator, in order to keep it on the optical axis of TL.
  4. After finding the right alignment through the separator, set the tilt so that the axis of the objective lens overlaps with that of TL and FL. That is the image pulsation caused when toggling OBJ should be centered on the mark indicating the axis of TL and FL. After setting the tilt, you might check again TL and FL.
  5. Align IL (IL aligners), P1 (P1 aligners),
  6. Check Acc Lens (only SEL to minimize the motion), align Inner Lens (minimize motion with Ret Lens Aligners).
  7. Acc Lens again (SEL + Acc Lens aligners). Before doing that, toggle P2 (make sure P2 align Y = 0), mark its center. Then use Acc Lens Aligners 1&2 to move the center of AL toggle as close as possible to the P2 mark. The combination of AL aligners 1&2 can stabilize the center of AL toggle anywhere along a line.
  8. Align P2 (mostly P2 aligner X, but also Y), and then P3 using the respective aligners.
  9. Lastly, toggle SEL, minimize with Acc Lens.
  10. After completing the alignment using PEEM, align the LEEM e-gun so that is centered on the area imaged by the PEEM. Go to MEM-LEEM transition, use CL3 to increase divergence of the beam, then center the interaction zone using ill. defl. X,Y, and use obj.aligners to center the entire electron beam within the view. After modifying the obj. aligners, note that the tilt has to be corrected.
  11. Once you have the LEEM working, you can improve alignment at high magnification.
  12. To check whether the important imaging planes are imaged correctly, do the following:
    1.      Toggle SEL, minimize movement with Acc Lens value, that is you optimize the Acc Lens focus. Check also the focus of the analyzer Inner lens
    2.      Toggle image equalizer (X or Y, does not matter), adjust the Field Lens value.
    3.      To check the TL value and the diffraction stigmators, insert contrast aperture CA30. When TL is too large or too small, the illuminated area becomes smaller than the field of view. Using the diffraction stigmators make sure that this area is circular. The correct TL value should maximize/homogenize the illumination in the field of view.
    4.      Check P1 lens value by inserting an energy slit (e.g. ES60). Maximize and homogenize the illumination by changing P1 value.

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Ultima modifica il Sabato, 29 Gennaio 2022 17:57