meta data for this page
  •  

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revisionPrevious revision
Next revision		Previous revision
projects:stm:log [2025/06/29 17:52] – [Day 2025-06-29 (rahix, k8ik, q3k)] rahixprojects:stm:log [2025/08/03 15:56] (current) – [Day 2025-08-02 (k8ik, q3k, rahix)] rahix
Line 1: Line 1:
 ====== Lab Notes for the Scanning Tunneling Microscope ====== ====== Lab Notes for the Scanning Tunneling Microscope ======
  
 +==== Day 2025-08-02 (k8ik, q3k, rahix) ====
 +Tried imaging the DVD surface under the SEM for reference.  Had a bit of trouble getting an image to become visible -> turns out that the surface is only visible at low acceleration voltages and becomes very invisible the higher it gets.  Finally worked well at 5kV and using SE imaging mode.
 +
 +The samples were prepared by lifting the bottom plastic off the DVD such that the aluminum foil sticks to the remaining plastic which also has the label printed on its back.  So we are looking at the sample from the same side as the DVD drive laser.
 +
 +{{:projects:stm:dvd-surface-uncalibrated.png?400|}}
 +
 +(The dimensions are off, because of our SEM not being calibrated properly)
 +
 +We now know that our samples are good and we should be able to image them on the STM!  Also found some prior art of imaging DVD surfaces with an STM, further corroborating that this approach will work: 
 +
 +  - [[http://www.joniemeyer.com/jo_niemeyer/STM.html|jo niemeyer STM]] ([[https://web.archive.org/web/20210518134908/http://www.joniemeyer.com/jo_niemeyer/STM.html|archive.org]])
 +  - [[https://hackaday.io/project/29332-the-pvc-scanning-tunneling-microscope/log/81900-samples-to-use-on-the-stm|DVD+R imaging on the "PVC scanning tunneling microscope"]]
 +==== Day 2025-07-12 (k8ik, rahix) ====
 +Rebuilt the experiment to the last state (oscillscope for live viewing, red pitaya for acquisition and x/y control, lab power supply).
 +
 +Made a new tip to reproduce tunneling.  Experimented a bit with different tip cutting strategies to see whether we can improve our results with better tips:
 +
 +  * Tried cutting a tip flat, without pulling
 +    * Seeing very weird offset currents when getting somewhat close to the sample.  These are definitely not tunneling effects.
 +    * The offset seems to throw off the PI controller quite a bit
 +    * Not able to achieve much stable tunneling
 +  * Tried cutting a tip at an angle, but with much less pulling force
 +    * Very very good results, achieving tunneling got considerably easier
 +    * Almost no hysteresis around the probe touching distance, making coarse approach very easy
 +    * Hypothesis: The tip is now much more stubby which makes it less prone to bending during sample contact.
 +
 +Also started to put more effort into making sure the tips are inserted straight into the STM.
 +
 +Made the C7 capacitor hack more permanent by soldering the capacitor to the respective terminals rather than wiring it in with alligator cables.
 +
 +New address for the Red Pitaya Notebook: http://redpitaya.lab.fa-fo.de/jlab/lab/tree/RedPitaya/Fafo/STM_Control.ipynb
 +
 +Wrote a new script for sweeping one of the red pitaya: http://redpitaya.lab.fa-fo.de/jlab/lab/tree/RedPitaya/Fafo/STM_Sweep.ipynb
 +
 +Connected the output of the Red Pitaya (CH1) to the X input of the control box.
 +
 +Added a 1k resistor parallel to ''R17'' to increase the X-axis gain from 1 to 11.  This means the input voltage is now -1V to 1V rather than -10V to 10V.
 +
 +Managed to take some sweep recordings while the STM was tunneling:
 +
 +{{:projects:stm:2025-07-12_23-34-scan.png?400|}}
 +{{:projects:stm:2025-07-12_23-35-scan.png?400|}}
 +
 +We definitely can't see any surface here, but we could reliably observe that the X movement slowly moved a stable tunneling out of range.
 ==== Day 2025-06-29 (rahix, k8ik, q3k) ==== ==== Day 2025-06-29 (rahix, k8ik, q3k) ====
  
Line 24: Line 69:
 {{:projects:stm:screenshot_from_2025-06-29_18-30-04.png?400|}} {{:projects:stm:screenshot_from_2025-06-29_18-30-04.png?400|}}
  
-Right now the script is still very unusable, even for pure acquisition.  We assume a problem is that the decimation factor is way too high at the moment.+Right now the script is still very unusable, even for pure acquisition.  We assume a problem is that the decimation factor is way too high at the moment.  We should also look into what RP calls "Deep Memory Acquisition" to not be limited to the 16k sample buffer size.
  
 Started making a bunch of new tips to see whether there is significant difference between them.  There is, some tips are way easier to get to tunnel.  => We need to work more on tip making skills to get reliable results here. Started making a bunch of new tips to see whether there is significant difference between them.  There is, some tips are way easier to get to tunnel.  => We need to work more on tip making skills to get reliable results here.