Friday, May 6, 2011

DIY Scanning Electron Microscope - Image Quality Improvements 2

I've made some improvements to the microscope that have increased image quality somewhat. Here is a quick list of the changes:

-Made a new acrylic light guide that allows the scintillator to face the sample directly. The pipe is curved so that the light is directed upwards into the photomultiplier tube. The size of my bell jar necessitated that the PMT be mounted vertically, which is not good since a straight light pipe would cause the scintillator to be aimed directly at the bottom of the chamber.

-Added coaxial cabling and a fully-shielded box to the PMT amplifier circuitry.

-Adjusted PMT load resistor, and eventually installed a potentiometer so that I can change the load resistance to best match the raster scan rate

-Changed PMT amplifier circuitry so that the images are not inverted with respect to normal secondary electron micrographs

This is a MEMs gyroscope. I pried off the cover to expose the die.

This micrograph shows some structure on the die. Hopefully with better magnification and resolution, I'll be able to see the MEMs gyro itself.

It appears to me that the blurriness in these images is somewhat constant across all magnifications. This leads me to believe that focus is not the main issue, and that the problem is with PMT signal recovery. Scanning at a slower rate should help this, but the PMT amplifier is AC-coupled, so the scan rate cannot get too low, and I also cannot see the image on the oscilloscope at low scan rates -- making focus and various other adjustments difficult. I also haven't found a good way to synchronize my camera shutter to the raster scan.


  1. Incredible machine you have built yourself.

  2. Ben,

    We met at maker faire but I failed to get your contact info. We will be powering up the Noisebridge SEM at 7pm tonight. Please stop in. Sorry for the short notice. Send me a message on the Noisebridge SEM mailing list.

    Chris Murphy

  3. Chris, sorry that I missed you. You can email me: ben at magconcept com. I'll check out the Noisebridge mailing list. Let me know when you guys will be using the SEM again, and I will see if I can make it.

  4. Hi Ben, I'm a researcher and SEM operator in the nanotech industry, and seeing someone make their own SEM is simply awesome. Could the blurriness in the images be due to aperture misalignment or stigmation issues? Also, what is your working distance? Great job here, I'll be following and watching for updates!

  5. Hello Ben. Could you tell me what is the voltage of the first focusing lens (aluminium tube between 2 copper pipes), is it the same as filament ?

  6. Ravaner, the first lens is known as a condenser lens, and it has the same potential as the wehnelt cylinder in the electron gun. This means that as the acceleration voltage of the electron gun is changed, the voltage on the condenser lens also changes, thus maintaining approximately the same focal length. Faster moving electrons (generated by higher acceleration voltages), will need to experience a higher electric field to be deflected an equal amount.