[NewCandle] Nick's new pics

[Nick Reiter]

Good morning, John and all,

Thank you for pointing out some aspects I will surely
check into.

The software I use in the EDS has the feature of being
able to show the different excitation lines for the
bands such as Kalpha, Lalpha, Lbeta.  Unless the
double excitation of the Al is an artifact that is
apart from the known excitation spectra, then it
seemed pretty pristine to me.

I run the EDS at 30 kV typically, sacrificing delicate
surface analysis for a full look at heavier species -
in my "day job" I typically have to look for Cd, Te,
Sn, Mo.

I guess I have a couple of counterpoints to yours:

1.  A scan taken of the same foil in a control or
un-processed state - a witness piece - at similar mags
and same kV does not show the presumed Ag peak in
question, even with the vertical scale stretched out,
as I did on some shots showing the Ag.

2.  The Yttrium peak, also quite significant IMO, is
as well something that appears to be genuinely related
to the processed material in question, not an artifact
of the process.  I attempted to scrutinize it to the
same dgree as the Ag, by using the different spectral
lines of neighboring elements to look for overlay,
etc.

3.  I'll accept the tag "inexperienced" graciously, as
I know that there is still much I have yet to learn
from lab analysts who have used SEM and EDS for more
exotic feats of detective work than I have, and for
more years.  On the other hand, I've been running EDS
for analysis in my workplace(s) for 16 years also -
mainly electronic metals, II-VI compounds, and
chalcogenides.  I like to consider myself maybe upper
elementary or middle school at least.

Still, it is certainly worthwhile to verify spectra by
looking for other more distant lines, as well as the
3.151 56% line you point out.  And to see if I can
chemically concentrate the unusually appearing
materials for better assay.

nr

> Thanks for the occasional excitement!  But I am
> sorry to say that it 
> looks like this anomaly might be inexperience with
> EDS and SEM.  I hope 
> I am wrong but it does seem that your Ag peak is
> uncomfortably close to 
> being 2xAl peak.  Also your Al peak is so high it
> goes way off the plot, 
> at which point it becomes natural that you should
> start to see the 
> "harmonics" due to counting of the occasional but
> unavoidable double hits.
> 
> For those who are not familiar with EDS, I will
> describe very briefly 
> how the process works (I know very little about the
> business, but have 
> attended a course and dabbled with one a few times).
>  The high energy 
> (usually 5-40kev) electrons, knock electrons which
> are in the elements 
> of the sample out of their orbits and when an
> electron spirals back in 
> to take its place, it emits an X-ray photon
> characteristic of the energy 
> level of the orbit and thus the element.  These
> photons plough into the 
> semiconducting detector crystal releasing
> electron-hole pairs (I assume) 
> which are picked up as a short pulse by a very
> sensitive charge 
> amplifier.  The energy of the photon is indicated by
> the size (ie number 
> of electrons) of the pulse and this size indicates
> which bin on the 
> spectrum this pulse should be accumulated into. 
> Well of course if you 
> get two photons hitting the detector in a time that
> is too short for the 
> pulse discriminator to discriminate, then they will
> be counted as a 
> single double-size (ie double energy) pulse.  So two
> aluminum pulses (of 
> 1487ev) arriving within a very short time of each
> other will look like a 
> single double energy (2974ev) pulse which may be
> indistinguishable from 
> a silver pulse (2984ev).
> 
> There are several ways to discover if this is the
> problem or not.  The 
> simplest is to halve the beam current and count for
> double the length of 
> time.  Since the length of each pulse remains the
> same, but you have 
> doubled the average time between pulses, you expect
> the number of pulse 
> overlaps to go down by a factor of two.  Similarly
> you can do the 
> opposite - double the beam current and count for
> half the time.  In 
> these cases you expect to get much the same reading
> for the aluminum 
> peak, but a *pseudo* silver peak that changes by
> factor of 2 each time!
> 
> Another method is to change the electron energy (ie
> change the KV 
> setting) in an attempt to excite another (usually
> higher) orbital energy 
> in the silver atoms that is not so close to being
> double the energy of a 
> peak in the aluminum.  Silver has some lines above
> 20kev whereas 
> aluminum has none - this would differentiate them
> immediately.
> 
> Actually quick look at some charts on the web
> suggest that silver should 
> have a reasonably bright (56%) line at 3151 in
> addition to the (100%) 
> line at 2984 that you are probably mis-identifying. 
> There is no 
> indication in these plots that your silver has such
> a double peak.  So 
> sorry to say, I think your Ag line is an artifact of
> the EDS method of 
> pulse discrimination!
> 
> J.
> 
> Keith Nagel wrote:
> >
>
http://www.kpnconsulting.com/newcandle/download/nick2.htm
> >
> > Here are the new SEM and EDS pics. Enjoy!
> >
> > K.
> 
> 
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