I understand that Auger electrons are emitted when an electron falls from a higher energy level to a open inner shell and EDX uses electrons that fall from outer shells when an inner shell is kicked off. I also have read that AED has a higher spatial resolution but I don't understand WHY this spatial resolution is higher. What is different about the Auger electrons that increases resolution?

  • $\begingroup$ This reads like a standard homework question. What do you know about the differences of the two techniques? $\endgroup$ – Jon Custer Oct 1 '20 at 12:37
  • $\begingroup$ I have never used the techniques my self so all i know is the theory. In principal, when a beam of electrons is aimed at my material, a core electron will be kicked out leaving a hole. A higher energy electron will fall to fill that hole. When this happens it can either release an x-ray or it can dislodge another electron which would be an Auger electron. $\endgroup$ – Harley McFarlen Oct 1 '20 at 12:44
  • $\begingroup$ I realize that auger electrons have a small mean free path so they are less likely to reach the detector but how would this give better spatial resolution? I would have predicted this would give worse spatial resolution since your signal to noise ratio would be so low $\endgroup$ – Harley McFarlen Oct 1 '20 at 12:46
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    $\begingroup$ this is not a standard homework question but even when i post questions that have nothing to do with homework you all still say they are homework questions. So i don't even know what a "non-homework" question would look like at this point $\endgroup$ – Harley McFarlen Oct 1 '20 at 12:47
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    $\begingroup$ this was a discussion we had with 6 other people. this is called discussion, maybe things have changed since you took classes but nowadays sometimes people have discussions in seminars and we walk away with questions that we want to understand $\endgroup$ – Harley McFarlen Oct 1 '20 at 12:50

I think this is a good question. The problem is more fundamental. In both cases, you would be using electron beams on the sample.

In EDX, you are shining a beam of electrons and detecting the X-rays. Here comes the main problem. It is hard to focus the X-rays. Mea culpa here. As Jon commented it is the depth of penetration of the electron beam and the corresponding X-ray emission that main affects spatial resolution. This picture roughly tells the story:


Auger electron electron spectroscopy, you are focusing a beam of electrons and you detect electrons. It is relatively easy to focus electrons using "lenses". Hence you can point point the exact origin where the electrons are being ejected.

Also, think about the depth profiling. EDX is not a surface technique unlike Auger. I used to have this misconception until I attended a workshop on surface analysis. The electrons can easily penetrate the sample and similarly originate from the some depth as well.

  • $\begingroup$ The 10's of kV incident electrons penetrate into the sample. The 100's of eV Auger electrons only escape from a shallow depth. In contrast the x-rays generated in EDX escape from a greater depth. It is this difference that leads to the resolution difference, nothing to do with 'focusing' or not of the x-rays. They come from a greater volume of material. $\endgroup$ – Jon Custer Oct 1 '20 at 15:16
  • $\begingroup$ Thanks for the pointer. Do surface scientists distinguish surface (x-y plane) vs. depth resolution (x,y, z) resolutions? $\endgroup$ – M. Farooq Oct 1 '20 at 15:54
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    $\begingroup$ The problem is that the incident beam blooms out laterally as it goes through the sample, so x-rays generated below the surface come from a larger lateral dimension than the incident beam. This means that the x-ray 'source' is bigger than the beam in x-y and can come from a greater depth range. In contrast, the Auger electrons only get out from the near-surface region, and there has not been much beam blooming by then. So, for Auger vs EDX the two (lateral and depth) go hand in hand. $\endgroup$ – Jon Custer Oct 1 '20 at 15:59
  • $\begingroup$ Thank you, I really appreciate you taking the time to answer. $\endgroup$ – Harley McFarlen Oct 1 '20 at 21:44
  • $\begingroup$ Also, note that one is not getting position information through 'imaging' the electrons of x-rays. The incident electron beam (perhaps 5-10 nm in diameter) is scanned in x and y, and counts at the detector are attributed to the current beam position on the sample. $\endgroup$ – Jon Custer Oct 2 '20 at 14:37

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