Monday, September 1, 2014

Electron microscope image capture with an oscilloscope

I show how I collect digital electron microscope images with my Tek MDO3000 oscilloscope.


  1. Hi Ben,

    Interesting video as always. Never really thought of using oscilloscope to capture images.

  2. I realize this may not be possible to adjust with your free(!) microscope, but what if instead of lingering over the same spot and shooting it with multiple electrons for your high res image, you could move the beam a tiny tiny bit and shoot one electron at each spot - then move to the next? Blasting too many electrons at the same spot, as you said, doesn't work because of the dispersion for electrons repelling each other. So you would still be limited in the rate, but not by as much.

    Also maybe it could be possible to use an algorithm like SACD used for higher frequency sampling of a single bit to create a more detailed waveform? (They used a 1 bit stream around 2Mhz instead of 16 bits at 42khz - like PCM).
    Just an idea...

  3. Max, what you describe is actually how the SEM works. In order to simplify the process, I described pixels in my video, but in reality, the electron beam is constantly moving. The system is completely analog, so values are accumulated as the beam is in motion. If it moves more slowly, there will be a higher number of measurements per unit length, but there aren't any pixels or dwell spots in the beam's path.

    The electron signal from the sample is a lot like a 1-bit stream. The secondary electron detector doesn't measure the energy of each electron -- just the total number collected. This means that it is a sort of very low-level digital signal of sorts. The pulses from each electron are sent through a low-pass filter which converts them into an analog value that corresponds with the number of electrons per second. With modern high-speed digital circuitry it might be possible to count electrons one-by-one, but I'm not sure this would be better than filtering and measuring.