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projects:stm [2025/05/28 09:56] – created rahixprojects:stm [2025/08/07 22:21] (current) – [STM key information] rahix
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-Building a **Scanning Tunneling Microscope**.+(Re-)building a **Scanning Tunneling Microscope** (STM).
  
-Repository with more info: https://git.fa-fo.de/fafo/k8ik-stm+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|}} 
 + 
 +[Current working state of the experiment] 
 + 
 +==== Links ==== 
 + 
 +  * [[https://git.fa-fo.de/fafo/k8ik-stm|git repository with technical documentation]] 
 +  * [[projects:stm:log|Lab Notes]] 
 + 
 + 
 +==== 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. 
 + 
 +The tip is made from tungsten wire and mounted to the scanning head using a screw terminal. 
 + 
 +To be documented. 
 + 
 +=== 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. 
 + 
 +The tip/probe is mounted slightly in front of two of the screws with the last one sitting very far back.  This makes a fulcrum with the back screw having even more fine adjust (factor 20). 
 + 
 +Thread pitch of micrometer screws (according to lab book 16.3.2012):  
 +  * Front 0.25mm per revolution 
 +  * Back 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-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)]] 
 +  * [[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)]] 
 +  * [[https://www.e-basteln.de/other/stm/references/|STM References Overview — Jürgen Müller (2006)]]