Talk:Auger electron spectroscopy
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Whomever wrote this page should add something about how this is a non-destructive surface analysis technique. Also, if anybody has a graph of an Auger spectrum, please post it. One last thing, explaining that the incident kinetic energy is not necessarily the same as the exigent kinetic energy of the electron because of all of the transitions that could occur is a little weak.
[unsigned comment left Sept 14, 2006]
I'd like to suggest that the process be described a little more clearly - right now I'm reading between the lines a lot, but it sounds like the process is:
an X-ray (from where? A brehmstrahlung X-ray tube? A syncrotron? I"m guess the former, if the energy is in the range of keV) strikes the sample
the X-ray is absorbed by an electron in one of the core atomic energy levels, which is excited out of the atom entirely (a "photoelectron")
the now-empty core state is now filled by another electron from the atom (the article says "outer shell" - is this necessarily so, or just what's useful for this process?)
if the energy difference between the core level and the level that the filling electron came from is greater than the energy difference between the outer shell and the vacuum, then an outer electron can be excited away (and presumably this one is the "auger electron") from the atom (leaving it now at charge 2-, since the x-ray photoelectron is gone, too), with any leftover energy contributing to the kinetic energy of the Auger electron.
What's the basis for the analysis? Is this a pulsed X-ray time-of-flight system?
Beakdan 15:22, 30 July 2007 (UTC)
To whomever posted the first comment, please be advised the AES is actually a destructive technique unlike XPS which is a non-destructive technique. Organic compounds such as cotton can decompose under auger analysis, and films such as titanium nitride grown by atomic layer deposition (ALD) have been sputtered off the surface by the auger beam during analysis. Also, a build up of adventicious carbon from the auger filament (in the case of electron excitement) has also been seen. this is the primary disadvantage of auger over XPS is that it can destroy samples. However, AES is much more sensitive than XPS (between 0.1-0.6% according to physical electronics) which is a definate advantage for the process.
To Beakdan, the x-ray source can be a simple copper or aluminum source as seen with XPS. XPS goes generate AES electrons as can be seen towards the lower energy end of XPS spectra (typically just labeled AES electrons). An electron beam can be used as well. You are correct that a core electron is ejected (though not necessarily the 1s electron), and is filled by one in a shell that is directly above the energy level of the electron ejected. So for a 1s electron, this vacancy can be filled by a 2s or 2p electron (a KLL transition). another electron is ejected from this high level (2s or 2p for the previous case) and this ejected electron is the auger electron. the kinetic energy of this electron I don't think is related to the energy of the x-ray used, but of the energy of the electron that fell down from the higher energy level, though I am not entirely sure of that. the reason I say this is that the auger effect is fairly small compared to the x-ray flouresence that also occurs when a core electron is ejected. I believe that the kinetic energy of this electron is related to the energy that the higher level electron would have flouresced had it chosen to do so. charge build up is a problem seen with AES as you noted with the -2 charge, which is why conducting or semiconducting samples are needed.
I'm not too sure what you mean by "basis for the analysis." I can only speak from experience using an electron beam to excite samples. the excitation source was run continously and an analyzer adjusted polarity between two plates to filter electrons out by kinetic energy. from there, signal versus kinetic energy was determined. to actually analyze the data, typically a derivative of the data is taken and compared to standard spectra for elements. all elements have transitions at various kinetic energies with various shapes depending on the electrons available for ejection. for example, the carbon KLL and the ruthenium LMM transitions are at about the same kinetic energy, but ruthenium transition looks sinusoidal while the carbon transition goes up a little bit, falls off drastically, then quickly levels off. titanium and nitrogen have a similar problem because the LMM and KLL peaks, respectively, are on to of one another making quantification of their concentrations incredibly difficult.
Thinfilm. —Preceding unsigned comment added by 128.111.150.85 (talk) 17:10, August 29, 2007 (UTC)
