Science > Physics > Auger electron spectroscopy (AES) spectrum question
| Topic: |
Science > Physics |
| User: |
"Marko" |
| Date: |
13 Oct 2003 05:40:52 PM |
| Object: |
Auger electron spectroscopy (AES) spectrum question |
Hello!
In Auger electron spectroscopy (AES) which in used in analyzing
surfaces of conducting and semiconductions solids, Auger electrons are
emitted and their energy is measured, since every different chemical
element (not hydrogen or helium) gives different energies for emitted
electron, we are given a method of determining the chemical
composition and the concentration of chemical elements at surface of a
solid sample.
The result is presented often as a graph, with ordinate N(E), giving
intensity (counts per second) and abscissa E, gives the energy in eV.
The graph shows how the intensity varies with energy, this is called
Auger spectrum in AES.
Where the intensity is highest there is highest concentration of that
specific chemical element which emitted Auger electron energy is equal
to the value of energy, E giving maximum value of intensity, N(E).
To better see were the maximum variation are, the graph given instead
show differentiated Auger spectrum, that is the ordinate is N'(E) and
absicssa is E.
What is interesting here is where the peaks are lowest, this according
to Auger Handbook gives what chemical element are at surface.
My question is why are the lowest peaks, minimum values of
N'(E)interesting?
Since, according to differential calculus, this gives the minima of
N(E), at points left of lowest point of N'(E), N'(E) is decreasing,
and at right of this point N'(E) is increasing, this gives that this
peak gives minumun of N(E), so why are minimum peak interesting in
Auger electron spectroscopy, since lowest peaks in differentiated
Auger spectrum doesn't show where the intensity is maximum instead it
shows where the intensity is minimum.
Thanks for your help!
Marko
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| User: "Mark Tarka" |
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| Title: Re: Auger electron spectroscopy (AES) spectrum question |
14 Oct 2003 09:01:20 PM |
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(Marko) wrote in message
news:<4325b260.0310090922.2c919054@posting.google.com>...
In Auger electron spectroscopy (AES) which in used in analyzing
surfaces of conducting and semiconductions solids, Auger electrons are
emitted and their energy is measured, since every different chemical
element (not hydrogen or helium) gives different energies for emitted
electron, we are given a method of determining the chemical
composition and the concentration of chemical elements at surface of a
solid sample.
The result is presented often as a graph, with ordinate N(E), giving
intensity (counts per second) and abscissa E, gives the energy in eV.
The graph shows how the intensity varies with energy, this is called
Auger spectrum in AES.
Where the intensity is highest there is highest concentration of that
specific chemical element which emitted Auger electron energy is equal
to the value of energy, E giving maximum value of intensity, N(E).
To better see were the maximum variation are, the graph given instead
show differentiated Auger spectrum, that is the ordinate is N'(E) and
absicssa is E.
What is interesting here is where the peaks are lowest, this according
to Auger Handbook gives what chemical element are at surface.
My question is why are the lowest peaks, minimum values of
N'(E)interesting?
Since, according to differential calculus, this gives the minima of
N(E), at points left of lowest point of N'(E), N'(E) is decreasing,
and at right of this point N'(E) is increasing, this gives that this
peak gives minumun of N(E), so why are minimum peak interesting in
Auger electron spectroscopy, since lowest peaks in differentiated
Auger spectrum doesn't show where the intensity is maximum instead it
shows where the intensity is minimum.
It's been sooooo long....
Have I got this right...the first derivative
will locate a maximum or minimum, the second,
a point. The max or min is found where the
the slope is zero...a very low number on a
scale like {0,n}.
The point of the N'(E) graph is to more accurately
determine the energy maximum for that particular
event (absorption?). This shows up as undergraduate
USA PChem lab trick...IIRC it's a technique used in
an accurate determination of the endpoint of a
titration: the first derivative of the data gives
a sharp positive Lorentzian-like peak, while the second
yields in part a straight line crossing the x-axis
(volume of titrant), coming as a result of the
change in slope of the sigmoid curve at the
point of neutralization/equivalence. I'm assuming
that the change in slope of an energy absorption
envelope, N(E), would provide the same info.
Mark (Just what the heck is Auger Spectroscopy, anyway,
something to do with citrus beverages?)
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| User: "" |
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| Title: Re: Auger electron spectroscopy (AES) spectrum question |
14 Oct 2003 03:09:11 PM |
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(Marko) wrote in message news:<4325b260.0310090922.2c919054@posting.google.com>...
Hello!
In Auger electron spectroscopy (AES) which in used in analyzing
surfaces of conducting and semiconductions solids, Auger electrons are
emitted and their energy is measured, since every different chemical
element (not hydrogen or helium) gives different energies for emitted
electron, we are given a method of determining the chemical
composition and the concentration of chemical elements at surface of a
solid sample.
The result is presented often as a graph, with ordinate N(E), giving
intensity (counts per second) and abscissa E, gives the energy in eV.
The graph shows how the intensity varies with energy, this is called
Auger spectrum in AES.
Where the intensity is highest there is highest concentration of that
specific chemical element which emitted Auger electron energy is equal
to the value of energy, E giving maximum value of intensity, N(E).
To better see were the maximum variation are, the graph given instead
show differentiated Auger spectrum, that is the ordinate is N'(E) and
absicssa is E.
What is interesting here is where the peaks are lowest, this according
to Auger Handbook gives what chemical element are at surface.
My question is why are the lowest peaks, minimum values of
N'(E)interesting?
Since, according to differential calculus, this gives the minima of
N(E), at points left of lowest point of N'(E), N'(E) is decreasing,
and at right of this point N'(E) is increasing, this gives that this
peak gives minumun of N(E), so why are minimum peak interesting in
Auger electron spectroscopy, since lowest peaks in differentiated
Auger spectrum doesn't show where the intensity is maximum instead it
shows where the intensity is minimum.
Thanks for your help!
Marko
Coming from the XPS-corner, where the Auger Peaks are a by-product,
i'll try an educated guess.
The lowest absolute values in the differentiated graph are of interest
since they give the maxima as well. You can differentiate between
minima and maxima easily. the minima will be very wide (diferentiated
"noise" base line) while the maxima will be more discrete.
Since Auger peaks are wide signals, i guess it makes sense to work
with the diff-method.
I am afraid that you somehow mixed up something. If N'(E) is
decreasing left of the "lowest point" it means that the increase is
getting less, the closer you get to the lowest point. The decrease of
the increase means that the original is still going up -> towards a
maximum.
I am really sorry for that last sentence ;-)
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