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projects:stm:log [2025/09/06 01:00] – [Day 2025-09-05 (rahix)] rahixprojects:stm:log [2025/09/30 22:27] (current) – Remove nolink rahix
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 ====== Lab Notes for the Scanning Tunneling Microscope ====== ====== Lab Notes for the Scanning Tunneling Microscope ======
  
 +==== Day 2025-09-20 (rahix) ====
 +Modelled more of the as-built of the current STM setup in mechanical CAD so we have a reference model:
 +
 +{{:projects:stm:cad-stm.png?900|}}
 +==== Day 2025-09-07 (rahix) ====
 +Took the video capture from yesterday, of the beam bouncing from the STM off a mirror 2.35m away and back to the camera on the STM and ran some analysis on the data.
 +
 +Analysis works like this:  For each frame, we find the beam center.  Then we look at the spectral content of the displacement in X and Y directions.  Check the full notebook for details: ''Laser-Wobble.ipynb'' from [[https://git.fa-fo.de/fafo/k8ik-stm/src/branch/main/Calculations|Calculations/]] ([[https://git.fa-fo.de/fafo/k8ik-stm/src/branch/main/Calculations/rendered/Laser-Wobble.md|Rendered Notebook]]).
 +
 +Here is the final figure:
 +
 +{{:projects:stm:2025-08-07-vibration-spectral-density.png?900|}}
 +
 +The most interesting result is the peak highlighted by the red line.  The red line marks the theoretical resonance frequency of the vibration isolation system that we had calculated in the past.  Seeing a peak right at this frequency sparks a lot of confidence!
 +
 +The results are limited up the 15 Hz because of the 30 fps video capture.  But towards the right of the figure, the data becomes pretty meaningless anyway as the displacements are too small for the camera to pick up already.
 +==== Day 2025-09-06 (rahix, q3k, hugo) ====
 +Rebuilt the entire experiment to clean up the space and install some shelving.  All connections are remade but the setup has not been reverified to tunneling.
 +
 +Set up the laser again to make some more measurements of the beam.  The following pictures show the beam at different distances. Left to right: 50mm, 100mm, 200mm, 400mm.  The 400mm measurement includes a mirror which is why the orientation is flipped.
 +
 +{{:projects:stm:2025-09-07-beam-50mm.png?400|}}
 +{{:projects:stm:2025-09-07-beam-100mm.png?400|}}
 +{{:projects:stm:2025-09-07-beam-200mm.png?400|}}
 +{{:projects:stm:2025-09-07-beam-400mm.png?400|}}
 +
 +The size change derived from the FWHM in these pictures would be about 0.6mrad, but this is most likely not at all a dependable result.
 +
 +Set up the laser to bounce off a mirror 2.35m away and back onto the STM vibration isolated mount.  Installed a ø2mm aperture in front of the beam to slightly tighten the profile.  This way we can watch the beam jump around on the camera.  Recorded 8 minutes of footage in hopes that we can recover the low-frequency content of the vibration isolation transmittance from this.
 +
 +Turned on the STM again and managed to get (very very unstable) tunneling.  So everything was set up correctly again!  The tip is still the broken one from the failed runs last time.  Adjusted the sample holding to avoid the collision that happened back then.  The STM is currently not covered in aluminum.
 +
 +We noticed that the vibration isolation is bouncing around a lot more after the rebuild. It seems this is caused by it now standing on a different part of the table that is not rigidly fastened to the table frame.  We should put some effort into stiffening the table structure here.
 +
 +Here is an overview of the current status of the experiment after it was rebuilt:
 +
 +{{:projects:stm:pxl_20250907_031437285.jpg?600|}}
 +
 +  * Oscilloscope
 +    * Yellow: Z displacement (control variable, this is the "output" signal)
 +    * Pink: Tunneling current scaled to 0-5V
 +    * Blue: X displacement output
 +    * Green: X displacement input
 +  * Multimeter (set to DC voltage
 +    * Setpoint current (''Sollstrom'') in 1V/nA (so 0.100V is 100pA)
 +  * Laptop
 +    * Connect white USB cable from the Raspberry Pi Pico
 +    * Temperature Measurement using ''serial-monitor-rust'' as detailed on [[projects:stm:log#day_2025-08-23_rahix_q3k_rob_hugo|2025-08-23]]
 +  * Red Pitaya (not currently running)
 +    * Can also measure the Z displacement (''IN1'')
 +    * And output the X displacement (''OUT1'')
 ==== Day 2025-09-05 (rahix) ==== ==== Day 2025-09-05 (rahix) ====
 Set up the beam camera for a test whether this whole plan of using the camera for interferometry will work.  Pointed the bare cheapo laser diode at it. Set up the beam camera for a test whether this whole plan of using the camera for interferometry will work.  Pointed the bare cheapo laser diode at it.
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 Played a bit more with the [[https://git.fa-fo.de/fafo/k8ik-stm/src/branch/main/Calculations/Spring-Dimensioning.ipynb|calculations for the mass-spring-damper system]] to see where we are at, comparing to commercially available systems: Played a bit more with the [[https://git.fa-fo.de/fafo/k8ik-stm/src/branch/main/Calculations/Spring-Dimensioning.ipynb|calculations for the mass-spring-damper system]] to see where we are at, comparing to commercially available systems:
  
-{{:projects:stm:dampening-2025-06-08.png?nolink&400|}}+{{:projects:stm:dampening-2025-06-08.png?400|}}
  
  
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 Calculated the damping behavior of our setup: Calculated the damping behavior of our setup:
  
-{{:projects:stm:damping-ratio-2025-06-08.png?nolink&400|}}+{{:projects:stm:damping-ratio-2025-06-08.png?400|}}
  
 EMI Box: EMI Box:
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 Removed the formwork from the conrete block we poured on friday.  The block is so nice! Removed the formwork from the conrete block we poured on friday.  The block is so nice!
  
-{{:projects:stm:stm-concrete-weight.jpg?nolink&400|}}+{{:projects:stm:stm-concrete-weight.jpg?400|}}
  
   * Lessons learned:   * Lessons learned:
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 Poured a concrete weight for the vibration isolation system: Poured a concrete weight for the vibration isolation system:
  
-{{:projects:stm:concrete-pouring.jpg?nolink&400|}}+{{:projects:stm:concrete-pouring.jpg?400|}}
  
   * Lessons learned:   * Lessons learned: