Procedures of HIM Alignment

Source Tilt

1) Locate the dummy sample >> Zoom in such that the Field of view is 5um x 5um >> Find a clean & flat region >> Focus
Note: Otherwise there will be a feature in the background of the trimer

2) Use “Grab” rather than “Continuous mode” >> dwell time : 2 u Sec >> Scan size = 512 x 512
This is to reduce the chance of knocking off the atoms.

3) On the hardware, switch from "Normal" to "SFIM" to see the trimer.

4) Grab and Tilt X and Tilt Y (iteratively) >> Align the red cross (optical axis) to the center of the selected W atom
Make sure the “Mode” is GUN TILT.

5) When the selected W atom is centered against the optical axis, the beam current will be higher than that before the alignment
(a) Adjust the "Spot Control" such that the beam current goes to 1 pA, which is for normal imaging and fine patterning.
(b) The smaller the spot size, the higher the beam current.
(c) The spot control is related to the position of cross-over through an aperture, hence controlling the brightness.
(d) The lens 1 is the condenser lens, which controls the brightness; the lens 2 is the objective lens, which controls the focus.

6) Change SFIM mode to normal mode after finish alignment.
Don’t expose the trimer too long for alignment.

Gun Shift
Gun shift -> Astig -> Gun shift -> Astig

1) Locate the dummy sample and zoom in (FOV: 5 um x 5um) >> Find an object with sharp features with a joystick >> Focus
For every step in calibrations, ensure the image is well-focused.

2) We can use “Continuous Mode” >> Increase the scan speed using hardware until the dwell time is 0.1 u Sec.
So that the image is instantaneously captured without lag.

3) Wobbling the lens 2 by activating the Wobble “Small”.
If the gun shift is very small, you can zoom in further like 2 um.

4) Turn the "Shift X" and "Shift Y" buttons until the image is not shifting.
Ensure the Gun mode is the "Gun shift".
You can off the wobbling after initial corrections, and re-focus the image.

5) If the beam tilt and beam shift are below +/- 200 urad, the lens system should be reasonably well aligned.
A few tens should be fine, try to control the beam tilt and beam shift below +/-200 urad.

6) Deactivate wobbling after the alignment.

Astigmatisms
Gun shift -> Astig -> Gun shift -> Astig

1) In the “Continuous Mode” >> Find an object with good features >> Focus
Zoom in further like 2 um if you cannot find any astigmatism at 5 um.

2) Adjust the "Astig X" and "Astig Y" knob, until the image is no streak in a certain direction.
Ensure it is focused after each Astig X and Astig Y correction.

3) Gun shift and Astigs are corrected iteratively at least 2 times.
Note: If the beam astig is not corrected, then the beam shape is not circular when patterning.