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projects:stm [2025/06/07 23:41] – rahixprojects:stm [2025/09/20 21:33] (current) – rahix
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 We are currently in the process of getting an STM back up and running.  The hardware was inherited from a past project by one of our members, where it successfully imaged sample surfaces.  Now we are trying to improve on those past results. We are currently in the process of getting an STM back up and running.  The hardware was inherited from a past project by one of our members, where it successfully imaged sample surfaces.  Now we are trying to improve on those past results.
  
-{{:projects:pxl_20250607_233415336.jpg?1200|}}+{{projects:stm:pxl_20250607_233415336.jpg?1200|}}
  
 [Current working state of the experiment] [Current working state of the experiment]
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 +==== STM key information ====
 +
 +=== STM Scanning Head ===
 +The scanning head of our STM uses 3 piezo actuators oriented along the 3 cartesian axes.  We currently do not have data on their actuation range.
 +
 +{{:projects:stm:stm-piezos.png?600|}}
 +{{:projects:stm:pxl_20250920_212713202.jpg?600|}}
 +
 +  * 1: x-axis piezo
 +  * 2: y-axis piezo
 +  * 3: z-axis piezo (height)
 +  * 4: STM tip mount
 +
 +The tip is made from tungsten wire and mounted to the scanning head using a screw terminal.  From there, a very short length of coax-cable connects the tip directly to the preamplifier board.
 +
 +=== STM Mount ===
 +The STM mount consists of two aluminum plates which seat against each other precisely using a [[http://www.g2-engineering.com/technology-kinematics|kinematic mount]] made from 3 micrometer screws.
 +
 +{{:projects:stm:stm-kinematic-mount.png?600|}}
 +
 +The tip/probe is mounted slightly in front micrometer screws 1 and 2.  Micrometer screw 3 is sitting very far back.  This makes a fulcrum with the screw 3 having even more fine adjust (factor 20).
 +
 +Thread pitch of micrometer screws (according to lab book 16.3.2012): 
 +  * Front (screws 1 and 2) 0.25mm per revolution
 +  * Back (screw 3) is hence 0.0125mm per revolution or 12.5µm 
 +
 +=== Electronics ===
 +The control loop for running the STM in constant current mode is currently an entirely analog design.  There is a transimpedance amplifier which preamplifies the tunneling current with a gain of 10⁹ V/A.  This nicely maps pA to mV (and measured tunneling currents are in the hundreds of pA range).
 +
 +Learn more about the electronics here: [[https://git.fa-fo.de/fafo/k8ik-stm/src/branch/main/Electronics]]
 +
 +=== Vibration Isolation ===
 +
 +We have built ourselves a simple passive vibration isolation using tension springs and a large mass.  The intended damping element (an eddy current brake) did not end up working, but also wasn't really needed after all.
 +
 +{{projects:stm:stm-frame-cad.png?600|}}
 +
 +We have not measured performance, but the real world resonance frequency matches the calculations quite well. Here is the calculated transmissibility (blue curve):
 +
 +{{:projects:stm:dampening-2025-06-08.png?400|}}
 +==== Other Projects ====
 +There are quite a few other DIY/open STM builds out there.  Here are a few links for further reading:
 +
 +  * [[https://www.sciencedirect.com/science/article/pii/S2468067223001116|Open STM — Weilin Ma (2023)]]
 +  * [[https://github.com/MechRedPanda/red-panda-stm|3D-Printed STM — MechPanda (2023)]]
 +  * [[https://hackaday.io/project/29332-the-pvc-scanning-tunneling-microscope|The PVC Scanning Tunneling Microscope — Tom Ekkens (2018)]]
 +  * [[https://dberard.com/home-built-stm/|Home-built STM — Dan Berard (2017)]]
 +  * [[http://www.joniemeyer.com/jo_niemeyer/STM.html|Project  „20 steps“  into the microcosmos — Jo Niemeyer (2009)]] ([[https://web.archive.org/web/20210518134908/http://www.joniemeyer.com/jo_niemeyer/STM.html|archive.org]])
 +  * [[https://www.e-basteln.de/other/stm/overview/#start|Homebrew STM — Jürgen Müller (2006)]]
 +
 +==== Further resources ====
 +And finally, some more resources worth knowing:
 +
 +  * [[https://gwyddion.net/|Gwyddion]] — Free SPM (AFM, SNOM/NSOM, STM, MFM, …) data analysis software
 +  * [[https://dberard.com/home-built-stm/links/|Useful Links]] — Dan Berard (2017)
 +  * [[https://www.e-basteln.de/other/stm/references/|STM References Overview]] — Jürgen Müller (2006)