Ti in Quartz

[Probeman]

Please refer to this publication which describes these methods in more detail:

http://probesoftware.com/Ti%20in%20Quartz,%20Am.%20Min.%20Donovan,%202011.pdf

In case anyone would like to try and reproduce the trace calculations shown above in Probe for EPMA for themselves, I've attached the Ti in Quartz MDB file (also the Standard.mdb file since this older probe database does not contain the standard compositions).

[BenjaminWade]

Hi John and all
Again necroing an old thread, however I was just wondering peoples thoughts on background fits for Al in quartz due to the tail of the Si peak, as I am again attempting to dabble in Ti/Al in quartz. John your 2010 paper utilises a polynomial regression fit on a detailed WDS scan, however I was wondering if this was all done before you had implemented the multi-point fit into PFE? I guess my question is, is this still necessary, or is a good multipoint fit with a number of points either side and using PFE polynomial fit good enough? I am conducting wavescans at the moment and will try both methods, but was just wondering peoples thoughts.

Cheers

[Probeman]

Hi John and all
Again necroing an old thread, however I was just wondering peoples thoughts on background fits for Al in quartz due to the tail of the Si peak, as I am again attempting to dabble in Ti/Al in quartz. John your 2010 paper utilises a polynomial regression fit on a detailed WDS scan, however I was wondering if this was all done before you had implemented the multi-point fit into PFE? I guess my question is, is this still necessary, or is a good multipoint fit with a number of points either side and using PFE polynomial fit good enough? I am conducting wavescans at the moment and will try both methods, but was just wondering peoples thoughts.

Cheers

Hi Ben,

Hi John and all
Again necroing an old thread, however I was just wondering peoples thoughts on background fits for Al in quartz due to the tail of the Si peak, as I am again attempting to dabble in Ti/Al in quartz. John your 2010 paper utilises a polynomial regression fit on a detailed WDS scan, however I was wondering if this was all done before you had implemented the multi-point fit into PFE? I guess my question is, is this still necessary, or is a good multipoint fit with a number of points either side and using PFE polynomial fit good enough? I am conducting wavescans at the moment and will try both methods, but was just wondering peoples thoughts.

Cheers

Hi Ben,
No apology necessary.  This is old stuff but good stuff- and it's new to some people!

To answer your question: you could use the MPB method instead of an exponential or polynomial fit to deal with the tail of an interfering peak on the off-peak position.  The advantage of the MPB method is that it fits the actual shape of the continuum, and if you consider the extended tail of the secondary line as just more "background", then it should all come out fine.

I've got an example here for a weird test I did recently looking at possible oxygen in the carbon coat deposition. Here is the problem:



Notice that because of the large tails from the Fe La/Lb/Ll lines on the low side of the oxygen peak, I had to use 4 MPBs all on the high side of the oxygen peak and extrapolate using a polynomial function (I know, dangerous) underneath the O ka peak for the background intensity. 

By the way I got around 0.3 wt% oxygen (not thin film geometry corrected) for the carbon coated FeS2 and around 0.1 wt% oxygen in the uncoated FeS2 (the variance on both was around 100 PPM). So it seems that maybe we are adding oxygen to the surface with our carbon coater (the venerable Edwards 306A evaporator), but I want to do some more tests on cleaned Ge and Au.

[BenjaminWade]

Great, thanks John I will try both methods but will more than likely end up using the MP. I do love a good MP fit, there is something satisfying about it.
Interesting about the carbon coat...I wonder if its the same with ours. Would you be using Ge and Au due to the absence of tails on the low side or because they will be more resistant to potential surface oxidation for your test? or both?

[Probeman]

Great, thanks John I will try both methods but will more than likely end up using the MP. I do love a good MP fit, there is something satisfying about it.
Interesting about the carbon coat...I wonder if its the same with ours. Would you be using Ge and Au due to the absence of tails on the low side or because they will be more resistant to potential surface oxidation for your test? or both?

The possibility of less surface oxidation.  But please feel free to report results from your carbon coater as well...

[John Donovan]

Here's an interesting thing with the alternating on/off peak acquisition mode.  I went back to an old Ti in quartz run with 5 aggregate spectrometers and here is the alternating TDI plotted for just the first spectrometer.



You might convince someone that there is a downward trend over time, but seems like random statistics to me... Now here is all 5 spectrometers aggregated together:



The downward trend is now a little more convincing visually, but it still amounts to almost nothing correction-wise, at least under these conditions.  Still nice to see that confirmed rigorously.
john

[Gseward]

John,

If you don't mind, and have the info easily available, I'd like to see your PET/LPET high precision wavescans of the Ti ka background on synthetic SiO2. I can find examples of your Spectro 2 scan on the forum, but presumably you have similar wavescans for 3 (or 4?) other spectrometers. Do you have similar from your SX50 instrument also?? I am interested in the frequency and position of the 'holes' on other instruments.

Cheers,

Gareth

[Probeman]

If you don't mind, and have the info easily available, I'd like to see your PET/LPET high precision wavescans of the Ti ka background on synthetic SiO2. I can find examples of your Spectro 2 scan on the forum, but presumably you have similar wavescans for 3 (or 4?) other spectrometers. Do you have similar from your SX50 instrument also?? I am interested in the frequency and position of the 'holes' on other instruments.

Hi Gareth,
Great question!

Yes, I've only seen these "holes" in the continuum on some PET spectrometers, the LPET sometimes shows these effects even more.  There's also some issue with the tails of the peaks that are visible when you plot them on a log scale. 

It may be dependent on the orientation of the analyzing crystal at the time of manufacturing...  at least for PET/LPET crystals.  It would be interesting to see some data from JEOL PET crystals.

See files attached below.
john

PS Some of the data above was utilized in my 2011 Amer. Min. paper here:

http://epmalab.uoregon.edu/pdfs/3631Donovan.pdf

[Probeman]

At the recent EMAS meeting in Konstantz, Germany (a fantastic meeting by the way), someone asked me if these "holes" in the continuum could be sample related.

I was pretty sure they are only related to the Bragg crystal from secondary diffraction, but it's always good to test ones assumptions.  To start, here is a scan 15 keV, 100 nA, 220/sec per point in a synthetic SiO2 on :



These artifacts seem to be visible only in the large PET crystals (Mike Jercinovic: do you see these same artifacts in your VLPETs?), but on my sp3 LPET these artifacts are much smaller as seen here:



Now as for other matrices I ran Al2O3, Cr2O3 and NiO and they all show the same continuum artifacts, so this artifact is apparently specific to the Bragg crystal  as seen here for Al2O3:

[Mike Jercinovic]

Actually no, but this is because we sacrificed the sin-theta range below .32000 as the crystal is too big to fully enter the objective port.  This was to be able to get the background around UMb.  Had we thought about Ti at that time, we could have cut just a little more off of the corner to get down to this wavelength.  Next time!
If I recall, Dave Wark found these holes also on standard PET.  There may be an orientational aspect to this too, depending on how the crystal is mounted on the holder.  Part of why they show up on high count rate crystals is that they are high count rate crystals.  You obviously have to have sufficient precision on the WDS scan to see these.  This is part of the issue in trace element work is that evaluating the wavelength region at low precision relative to the actual peak counting precision can be really misleading.  But of course it takes forever to really do these sorts of high precision scans...hence the use of blanks, the PfE blank correction, and multi-point scanning!  Although, as you have shown, for a simple matrix like SiO2 the background may be done pretty well by MAN estimation.

[Dave Wark]

The "holes" were indeed found on both standard and large PET crystals, on JEOL and Cameca instruments. And they certainly are orientation dependent. We ended up swapping our PET crystals that showed the holes with new crystals (oriented differently) that did not show the holes.

[Falling Man]

I'm currently analyzing some additively manufactured TiO2-SiO2 glasses, and want to use multiple spectrometers with PET crystals to improve the count rates for Ti (samples have less than 1.5 wt% TiO2).  After analyzing my standards with 3 PET crystals, I analyzed my TiO2 standard and got totals of 212 wt% - much more than I'd bargained for.  I poked around until I found the "aggregate" check-box and all was well.  I was subsequently directed to this discussion and wish that I'd visited here first.  However, it is heartening to know that, starting from different points, multiple users can negotiate the PFE environment and get to the same place...

Now I'd like to make x-ray maps of the samples to compare with their index of refraction maps.  Can I similarly aggregate the counts from multiple spectrometers in Probe Image to improve the Ti images?

[Probeman]

I'm currently analyzing some additively manufactured TiO2-SiO2 glasses, and want to use multiple spectrometers with PET crystals to improve the count rates for Ti (samples have less than 1.5 wt% TiO2).  After analyzing my standards with 3 PET crystals, I analyzed my TiO2 standard and got totals of 212 wt% - much more than I'd bargained for.  I poked around until I found the "aggregate" check-box and all was well.  I was subsequently directed to this discussion and wish that I'd visited here first.  However, it is heartening to know that, starting from different points, multiple users can negotiate the PFE environment and get to the same place...

Hi Rick,
Very cool that you found this on your own!  I think the software also prints out a warning if duplicate elements are not aggregated, let me see if I can produce the warning... here it is:

WARNING- Duplicate analyzed elements are present in the sample matrix!!
Use Aggregate Intensity option or Disable Quant feature for accurate matrix correction.

Now I'd like to make x-ray maps of the samples to compare with their index of refraction maps.  Can I similarly aggregate the counts from multiple spectrometers in Probe Image to improve the Ti images?

Yes, absolutely.  You simply acquire standards in Probe for EPMA (with the duplicate elements) and maps in Probe Image (with the same duplicate element setup).  Then you combine these in CalcImage and utilize the same Use Aggregate Intensities for Duplicate Elements checkbox under Analytical | Analysis Options menu.

Here's a very pretty example of trace sulfur acquired by a student at Adelaide using multiple spectrometers:

http://probesoftware.com/smf/index.php?topic=41.msg2180#msg2180

john

[Probeman]

I was pretty sure they are only related to the Bragg crystal from secondary diffraction, but it's always good to test ones assumptions.  To start, here is a scan 15 keV, 100 nA, 220/sec per point in a synthetic SiO2 on :

Someone asked a great question at the Athens EPMA workshop on whether absorption edges and "negative" peaks have anything in common, and the short answer is "no". 

We didn't have time to go into this during the workshop today, but basically "negative peaks" or as some refer to them, "holes" in the background, are due to secondary Bragg diffraction in cases such as the hole under the Ti ka peak on some PET crystals as shown above, or as seen here near the Au Ma line:

https://probesoftware.com/smf/index.php?topic=980.msg8769#msg8769

Here is a citation for the hole near the Au Ma line:

Self, P. G., et al. "Holes in the background in XRS." X‐Ray Spectrometry 19.2 (1990): 59-61.

Absorption edges are quite different looking and are from the mechanism of x-ray absorption for energies just above the ionization energy of an element such as seen here:

https://probesoftware.com/smf/index.php?topic=32.msg1214#msg1214

This absorbing element can be either in the sample or the detector gas!