CALCZAF and correction of interference by subsidiary and higher order lines?

[Probeman]

Hi Jakub,
John Donovan here. I am responding as "probeman" since that is my academic login for the forum.

Here's an interesting thing. In the Probe for EPMA software there are two additional options for the interference correction. One, to perform the 1993 interference correction, but *without* a matrix correction for the interfering line to account for the differences between the unknown composition and the standard used for the interference correction calibration. And two, the original Gilfrich interference correction which only relies on a simple ratio of the intensities. As seen here:



The Pb La/As Ka interference is probably not the best example to try these options with, but let's just see what happens. So here is the PbSiO3 (alamosite) example from the previous post, using the 1993 correction, but without the matrix correction term for differences between the unknown composition and the standard used for the interference correction calibration:

St  386 Set   3 Alamosite (PbSiO3)
TakeOff = 40.0  KiloVolt = 20.0  Beam Current = 30.0  Beam Size =    0
(Magnification (analytical) =  40000),        Beam Mode = Analog  Spot
(Magnification (default) =      400, Magnification (imaging) =    800)
Image Shift (X,Y):                                         .00,    .00

Tsumeb, South West Africa
From Mineralogical Research, CA
(assumed stoichiometric)
Number of Data Lines:   3             Number of 'Good' Data Lines:   3
First/Last Date-Time: 05/25/2015 05:30:18 PM to 05/25/2015 05:35:33 PM
WARNING- Using Exponential Off-Peak correction for pb la
WARNING- Using Exponential Off-Peak correction for as ka

Average Total Oxygen:         .000     Average Total Weight%:   99.577
Average Calculated Oxygen:    .000     Average Atomic Number:   63.145
Average Excess Oxygen:        .000     Average Atomic Weight:   56.780
Average ZAF Iteration:        4.00     Average Quant Iterate:    14.33

St  386 Set   3 Alamosite (PbSiO3), Results in Elemental Weight Percents
 
ELEM:        S      Pb      As      Si       O
TYPE:     ANAL    ANAL    ANAL    SPEC    SPEC
BGDS:      LIN     EXP     EXP
TIME:    80.00   80.00   80.00     ---     ---
BEAM:    29.88   29.88   29.88     ---     ---

ELEM:        S      Pb      As      Si       O   SUM 
   321   -.014  73.892  -1.109   9.910  16.939  99.617
   322   -.012  73.692  -1.054   9.910  16.939  99.475
   323   -.004  73.640   -.845   9.910  16.939  99.640

AVER:    -.010  73.741  -1.003   9.910  16.939  99.577
SDEV:     .006    .133    .140    .000    .000    .090
SERR:     .003    .077    .081    .000    .000
%RSD:   -56.98     .18  -13.93     .00     .00

PUBL:     n.a.  73.151    n.a.   9.910  16.939 100.000
%VAR:      ---     .81     ---     .00     .00
DIFF:      ---    .590     ---    .000    .000
STDS:      730     731     662     ---     ---

STKF:    .4736   .8044   .4976     ---     ---
STCT:   232.38  301.58   92.02     ---     ---

UNKF:   -.0001   .6275  -.0107     ---     ---
UNCT:     -.04  235.26   -1.97     ---     ---
UNBG:      .60   14.64    3.37     ---     ---

ZCOR:   1.1646  1.1752   .9398     ---     ---
KRAW:   -.0002   .7801  -.0214     ---     ---
PKBG:      .93   17.07     .41     ---     ---
INT%:     ----    ---- -104.55     ---     ---

It's actually somewhat better than with the matrix correction term! Again I suspect this is because the interference from the Pb La line on As relative to the Pb interference standard (galena), is not properly captured by the matrix correction term for As Ka.

And here is the sample again, but using the old Gilfrich interference correction:

St  386 Set   3 Alamosite (PbSiO3)
TakeOff = 40.0  KiloVolt = 20.0  Beam Current = 30.0  Beam Size =    0
(Magnification (analytical) =  40000),        Beam Mode = Analog  Spot
(Magnification (default) =      400, Magnification (imaging) =    800)
Image Shift (X,Y):                                         .00,    .00

Tsumeb, South West Africa
From Mineralogical Research, CA
(assumed stoichiometric)
Number of Data Lines:   3             Number of 'Good' Data Lines:   3
First/Last Date-Time: 05/25/2015 05:30:18 PM to 05/25/2015 05:35:33 PM
WARNING- Using Exponential Off-Peak correction for pb la
WARNING- Using Exponential Off-Peak correction for as ka

Average Total Oxygen:         .000     Average Total Weight%:   52.147
Average Calculated Oxygen:    .000     Average Atomic Number:   44.055
Average Excess Oxygen:        .000     Average Atomic Weight:   33.809
Average ZAF Iteration:        4.00     Average Quant Iterate:     2.00

St  386 Set   3 Alamosite (PbSiO3), Results in Elemental Weight Percents
 
ELEM:        S      Pb      As      Si       O
TYPE:     ANAL    ANAL    ANAL    SPEC    SPEC
BGDS:      LIN     EXP     EXP
TIME:    80.00   80.00   80.00     ---     ---
BEAM:    29.88   29.88   29.88     ---     ---

ELEM:        S      Pb      As      Si       O   SUM 
   321   -.015  24.574    .936   9.910  16.939  52.344
   322   -.013  24.358   1.003   9.910  16.939  52.196
   323   -.004  23.808   1.249   9.910  16.939  51.901

AVER:    -.011  24.247   1.062   9.910  16.939  52.147
SDEV:     .006    .395    .165    .000    .000    .225
SERR:     .004    .228    .095    .000    .000
%RSD:   -56.90    1.63   15.51     .00     .00

PUBL:     n.a.  73.151    n.a.   9.910  16.939 100.000
%VAR:      ---  -66.85     ---     .00     .00
DIFF:      --- -48.904     ---    .000    .000
STDS:      730     731     662     ---     ---

STKF:    .4736   .8044   .4976     ---     ---
STCT:   232.38  301.58   92.02     ---     ---

UNKF:   -.0001   .1797   .0099     ---     ---
UNCT:     -.04   67.36    1.84     ---     ---
UNBG:      .60   14.64    3.37     ---     ---

ZCOR:   1.2615  1.3495  1.0698     ---     ---
KRAW:   -.0002   .2234   .0200     ---     ---
PKBG:      .93    5.60    1.54     ---     ---
INT%:     ----  -71.37  -95.77     ---     ---

Not very good at all!  And in fact since the Gilfrich method was not iterated in its original implementation, it's doing better than it would have traditionally!

So the 1993 method is a definite improvement over Gilfrich as shown in the 1993 paper, but it could still be improved further as I hope you will be able to show, by utilizing the correct matrix correction term for the specific interfering line. 

One question that occurs to me is that how will you deal with a situation where more than one interfering line interferes with a specific analytical line.  Often we see a situation where several lines of different Bragg orders are involved in the interference.  The world is complicated!   

[sem-geologist]

I know this is old post, but I have I think something valuable to add to this topic.

First of all, Julien, correcting background interferences is not Insane at all. If You have all large diffracting crystals (worse resolution) and measured substances contains many elements (30+) -- there is no way for some elements to have a interference-free space even for a single-background measurement (and situation is outstandingly worse for mentioned multi background method). Actually, this kind of interference correction (of background) at last is possible starting with Peaksight 6.5, and it works just remarkably (unfortunately it is not documented in release note - IMHO that is the most important improvement in Peaksight ever). After finding it out I started to use it fully on one of our machines (SXFiveFE), where we have all large diff crystals - that is like heaven-sent feature. Currently I have about 120 interference corrections for HFSE+REE+PbThU+MAJOR (about 43 elements). I was finding like 200 interferences initially, but it was creating interference correction loops and correctness of those in case of many overlapping loops is questionable. Thus some of mesurements had to move to "creative, self-correcting" mode. Everything is measured on alpha, no beta lines measured anywhere. Most of my measurements are with single sided single background as then there is less background interferences to correct (unless two bkgd can give more tricks for "Creative-self-correcting"). When using "exponential" with Peaksight there is a small catch: it will be linear if higher sin theta bkgd is more intense, so it is not solution to all problems as it can bring in some not-linear response in minerals with high variable composition.

Anyway, Peaksight was doing iterative interference corrections (of peak interference) I don't know for how long - stating  "it's not doing that" is wrong. The only requirement stated for it to work in its documentation is to use Merlet's X-PHI. Talking about X-PHI, I find it very robust, in particularly that I see very good results with undervoltaged measurements (HREE+Hf,Ta,W lines on LLiF with 15keV beam), so that it does not require increase in voltage (classic approach, switching between 20 to 10kV), which preserves decent spatial resolution, and is in particular useful on FEG machine as it does not destabilize the cathode. I saw that NeXL has included X-PHI too. So there probably is a way to get that working in other sofware beside Peaksight.

As for negative interference (or bkgd interference) correction, the implemented way in Peaksight 6.5 works remarkably well. You can set background position even directly over other strong line of other element, even few elements, and that/those correction(s) will correct the intensity and measure it well. (I made few controlled tests to see that for myself). So background interference correction is not only NOT INSANE, but also a working reality.