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Circuit of a Scanning Tunneling Microscope (STM)

  1. Feb 4, 2006 #1
    Hi, for my integration class I am building a scanning tunnelling microscope (STM). I found some interesting designs and I choose the cheapest one (students are poor) witch uses a unimorph disk. The circuits are not that hard to build but I also need to understand them. I have some knowledge in electronics but not enough to understand every aspect of the electronics involved.

    Here are the circuits (sorry pdf): http://www.geocities.com/spm_stm/Simple_STM_Rev_C.PDF
    The circuits are mostly composed op-amp's wich i understand basicly but not enough to understand these circuits.

    So here are my questions:
    What are the effects of using a capacitor coupled with an op-amp (only used them basically with resistors)?
    On op-amp in D1-D2 what is connected to 1 and 5 and what is the use of 1-5?
    What are the TP (TP1,2,5,6)?
    Instead of using and BNC male connector output for the oscilloscope is it possible to use an audio like male connector and plug it into a computer sound card (analog2digital) and use a software oscilloscope?
    What are the uses of the potentiometers and how do they work?
    Can the circuits be improved?

    If you have any other suggestions don't be shy, I am opened to anything. Also don't be scared of being too technical, I will figure it out or read around to understand it.

    Thank you in advance.

    P.S. I will also post in the engineering design section and in quantum physics one for other questions. So if you are interested about other part or have a lot of knowledge on STM's you can go to the two other threads.
    Design engineering
    Quantum physics
     
    Last edited: Feb 4, 2006
  2. jcsd
  3. Feb 4, 2006 #2
    This is a very neat project. I've always wanted to do it but never had time.

    Here is another link:

    http://www.geocities.com/spm_stm/Project.html


    For your circuit you need 2 ramp signal generators which drive both the circuit to scan X and Y direction but also sweep a dot on the oscilloscope in X and Y direction, such that a pixel on the scope will correspond to an offset of the needle some micrometers away. Then the magnitute of the quantum tunneling will be amplified and applied to Z axis (brightness of pixel) on the scope. This should result in a nice scan.

    Since a PC sound card contains one ADC (analog digial converter) It will not work without some kind of synchronization.

    What are the effects of using a capacitor coupled with an op-amp (only used them basically with resistors)?

    Mostly to kill any oscillation or act as low or high pass filter.


    On op-amp in D1-D2 what is connected to 1 and 5 and what is the use of 1-5?

    sorry cant find it.

    What are the TP (TP1,2,5,6)?

    Tap points which are easily accessable points of wire where you can stick a voltmeter.

    What are the uses of the potentiometers and how do they work?

    Potentiometers are variable resistors when turned change resistance.

    Can the circuits be improved?

    O yeah, but its too advanced. You could drive X and Y with 2 DAC's (digital analog converter) and a microcontoller.
     
  4. Feb 4, 2006 #3
    I know that but I want to know more in debt to what i have to adjust them.

    Are you shure it wouldn't work? It looks it would work by looking at this software site (Digital Oscilloscope) but I can't tell... I was more scared about amperage or frequency of the output current then the card not converting properly...
     
    Last edited: Feb 4, 2006
  5. Feb 5, 2006 #4
    The potentiometers in the schematics are used to adjust the gain of the quantum tunneling amplifier.

    So while you are running the microscope you would adjust them for best possible picture.


    As for the PC sound card, does it have it 2 channels? and a third for Z axis?
     
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