Light Element Crystal Refractive Index Values

[Mike Matthews]

In case anyone wants hand-crank some energy to spec positions conversions:

  WDj = (24.792 x R)/(2d x E) or E = (24.792 x R)/(2d x WDj)

  WDc = (12.3986 x 100000)/(2d x E) or E = (12.3986 x 100000)/(2d x WDc)

Which means that:

  WDj = 0.0028 x WDc or WDc = 357.143 x WDj

To convert between wavelength and energy:

  L = 12.3986/L or L = 12.3986/E

where

  WDj and WDc are the JEOL and Cameca spectrometer positions respectively,
  R is the Rowland circle radius in mm (160 for Cameca and 140 for all three JEOL spectrometers),
  2d is the crystal lattice spacing in A,
  E is the X-Ray energy in keV
  L is the X-Ray wavelength in A

[Probeman]

And if you've ever wondered where the constant 12.3986 (or so) comes from...

[sckuehn]

How about adding the old school 127 mm Rowland circle from the ARL SEMQ?

[Probeman]

How about adding the old school 127 mm Rowland circle from the ARL SEMQ?

Hi Steve,
Sorry, starting in v. 10 of my software I removed all the ARL constants from my software- and you know what?  I'm not going to add them back in!

Sorry.   

[Probeman]

Thanks for the summary Owen, that's excellent.

John, my understanding is that both the JEOL and Cameca crystals come from the same supplier, they just name them differently, so the following are direct equivalents:

PC3 = LDE3
PC25 = LDEB
PC2 = LDE2
PC1 = LDE1
PC0 = LDE45

I'm not sure which PC, if any, is equivalent to LDE6 though.

I'm trying to remember the compositions of these multi-layers. I seem to remember that:

PC0 and PC1 are W/Si
PC2 is Ni/C
PC3 is Mo/B4C

I have a PC2.5 which is also Mo/B4C.
john

[Anette von der Handt]

One more overview, building on various literature, my notes and previous answers:


Cameca                  JEOL           d-spacing           Material
name                     name          (nm)

PC0                          -                 4.5                  W/Si
PC1                        LDE1             6                     W/Si
PC2                        LDE2           10                     Ni/C
PC3                        LDE3           20                     Mo/B4C
PC2.5/LBoron          LDEB           14.5                  Mo/B4C (careful: up to 0.5 wt% B2O3 fluorescence)
LNitrogen                LDE5             8                     Cr/Sc (careful: absorption edge under N)
      ?                      LDE6           12                     Cr/C

They all come from Ovonic/Ovonyx (now part of Rigaku) in Michigan*.

I wonder if there is C fluorescence from the LDE6 as well. Has anyone ever checked/seen that?


----
*From their web page: Ovonyx™ multilayer optics are the most popular light element X-ray analyzers for all wavelength dispersive spectrometer (WDS) attachments used on SEMs and in electron probe microanalysis (EPMA). Ovonyx Analyzers are sold to most major X-ray spectrometer manufacturers around the world including Cameca, Jeol, Oxford, Shimadzu, and Thermo Noran.

Current offerings:
Product series       Available 2d spacings       Primary elements    Secondary elements       Notes
"A"                       60Å                               F,O                       N      
"E"                       90Å                               N             
"N"                       80Å & 100Å               O,C,B               N      
"C"                       100Å                       C                       B                         no O interface
"H"                       145Å & 200Å               B                       Be      
"Y"                       145Å & 200Å               B                       Be                         Intensity ≥ 130%
                                                                                                                                           of H Series

I am curious about details on series "E"..

[Anette von der Handt]

Yes, LDEC seems to be an old name for LDE2. I found this: LDEC: 9.8 nm; Ni/C Layered Synthetic; Low High B-O (Kα), optimized for C analysis.

I never heard of LDE4 but I guess it must exist just for logical reasons (LDE1-6).

I would still say the Cameca equivalent to LDE5 is the LNitrogen (they offer this).

Cameca also has a Li-capable monochromator out now (see Goldschmidt 2017 abstract).

[Anette von der Handt]

I asked Pete McSwiggen about the LDE4. This is what he said:

"In regards to the LDE4 crystal, they used to have a LDE4H.  However, it seems to have been dropped as an option back at least at the beginning of the 8200 era.  I do not know what happened to it, but since it is no longer offered, I assume it was an under performer."

We can quiz JEOL at M&M and maybe find out more. I am also curious why they don't offer an equivalent to PC0.

[Julien]

Has anyone tested / calculated the actual 2d spacing of their monochromator? How accurate are the value provided by JEOL and Cameca? How about the refractive index? Is it fixed and physically determined in each material, or is it variable from monochromator to monochromator (or even from instrument to instrument???)?

Cheers,

Julien

[Probeman]

Has anyone tested / calculated the actual 2d spacing of their monochromator? How accurate are the value provided by JEOL and Cameca? How about the refractive index? Is it fixed and physically determined in each material, or is it variable from monochromator to monochromator (or even from instrument to instrument???)?

Cheers,

Julien

Hi Julien,
Good questions.  Yes, John Fournelle has done this.

See the PPT attached to this post (need to login to see attachments):

https://smf.probesoftware.com/index.php?topic=197.msg1732#msg1732

Also yes, the refractive index is determined by the composition and layer thicknesses of the multi-layer material. 

This window in CalcZAF allows one to see the effect of the refractive index on the spectrometer position:

https://smf.probesoftware.com/index.php?topic=598.msg4347#msg4347

The "K index" is the refractive index from the CRYSTALS.DAT file in the ProgramData\Probe Software\Probe for EPMA folder. 

john

[Anette von der Handt]

JEOL provides an inspection certificate stating the d-spacing for each LDE monochromator installed but not their refractive index. The values can vary quite a bit from machine to machine and crystal to crystal in my experience.

For example, on my new machine I have LDE1: 6.04 nm; LDE2: 9.86 nm; LDE6L: 11.86 nm. I have somewhere values from some other instruments. Let's see what I can dig up.

I haven't had a chance to cross-check mine yet but will report back what I find when I get to it.

[JohnF]

I have been asked to add my 2 cents here...

Recall that one typically peaks on an element of interest on a specific spectrometer bearing a specific crystal. Say F Ka on a nominal 45 A 2d diffraction. Thus the software will "automatically" set the spectrometer position, correctly showing the F Ka peak at the "published" position (whether sin theta, mm, A or eV). 2d and K refraction value are essentially non-observable. The point of having a correct 2d with correct K refraction value are that when one wishes to see higher order markers, they will fall in the right place. That is what I found years ago with the SX51 and good old PfW v9 (still running it on SX51).

A test to tell me if this is relevant. With say 60A diffractor, peak on O Ka on an aluminosilicate. Then in PHA mode integral, do a detailed slow wavescan,  for whole spectrometer range, and see if the 3rd order higher order peak markers for Al and Si (and maybe other elements too) line up with the observed peaks. If they do, hurrah, and no need to do anything. If they don't, then 2d and K need some adjustment.

John

[John Donovan]

Bringing this topic forward because a colleague of ours recently had an issue where the spectrometer position for oxygen on their LDE1 Bragg crystal was not being calculated correctly.  In fact it was off by ~2 mm!

Basically they need to perform the measurements documented by John Fournelle here:

https://academic.oup.com/mam/article-abstract/12/S02/836/6916142

I'll ask John for his Powerpoint for this procedure and post it here later...

In the meantime they can decrease the sensitivity of this peak offset error by editing this parameter in their SCALERS.DAT file on line 34:

400.    400.    400.    400.    400.  "Spec offset warning factors"

The sensitivity is calculated for each spectrometer as: (hilimit - lolimit) / specoffsetwarningfactor

So to (temporarily) decrease the sensitivity of this warning simply edit the 400 value on that spectrometer to a smaller number, say 300 and they shouldn't get any more warnings.

[Julien]

I believe we discussed this earlier in this thread... The real (mechanical) position of the peaks will first depend on the spectrometer initialisation (check min/max limit) and non-linearity (i.e., check position of several X-ray peak and apply a polynomial fit to the X-ray position to match the expected theoretical value). At least that's how JEOL is doing it...

Then, the problem is of course the accuracy of the 2d-spacing value and its famous refractive index "k" (see for instance S. Reed's book). In an earlier post, I had given a spreadsheet to calculate the 2d and the k index from a set of measurement to be done on each individual EPMA, quoted below. I guess not all diffracting monochromators are born equal

See the attached spreadsheet. It contains macro and use the Solver from Microsoft Excel to fit the 2d and k values based on a set of X-ray position measurement at different diffraction order n = 1 to 4. Instruction in the first sheet.

Julien

Alright, after a few hours of WDS scan on grand'ma JEOL-8600 (26 years old!), I got some results on the 2d-k evaluation on my available multilayers. Results on LDE1 (60 Å) are pretty consistant, independent on the X-ray line / order I choose for the regression. However, I cannot tell this for the other two large-2d spectro I have (LDEC ~100Å and LDEB ~150Å). Here it is (details in the spreadsheet):

- LDE1 (60 Å): 2d = 61.3 Å / k = 0.013
- LDEC (100 Å): 2d = 102.5 Å / k = 0.028
- LDEB (150 Å): 2d = 149.2 Å / k = 0.035

Now, if I exclude some "badly defined (high order) peaks"...
- LDE1 (60 Å): 2d = 61.3 Å / k = 0.014
- LDEC (100 Å): 2d = 102.8 / k = 0.031
- LDEB (150 Å): 2d = 150.0 / k = 0.041

Note that these values are NOT corrected for possibly dynamic (mechanical) shift... I cannot easily verify this (suggestions are welcome for this matter...), although if I assume a shift similar to the other crystals available (PET and TAP for spectrometer with LDEC and LDEB, TAP for spectrometer with LDE1), then here are the results:
- LDE1 (60 Å): 2d = 61.4 Å / k = 0.013
- LDEC (100 Å): 2d = 102.7 Å / k = 0.028
- LDEB (150 Å): 2d = 149.4 Å / k = 0.035
("of course" this shift chiefly affects the 2d of the crystal, not so much the k...)

See the XL spreadsheets for the results (one is a modified copy of the XL macro I wrote - see my former comment, the other are the acquisition results [peak positions]; these results are NOT corrected for possible dynamic shift, which are in the order of 0.1-0.2 mm on my JEOL-8600). I got these results using a high-beam current (most of them 200 nA, some 100 nA), with 2 to 4 seconds counting time (longer on high-order lines), and with a step of 0.1 mm or 0.00035 sin-theta (some 0.25 mm = 0.00090 sin-theta). These could have been refined using a smaller step size and longer counting time, but I did not have enough time to do this today... Also, keep in mind that ALL my monochromators are "normal" area monochromator... Hence the difficulty to get good precision on X-ray line above 3rd-4th order... Even on pure metals for L-lines...

@John Fournelle: maybe, can you suggest the conditions you've used for your WDS scan?

And for comparison, here are the data that John Fournelle mention in his PowerPoint (slide 19):
- PC0 (45 Å): old = 44 Å, 0.01483 => NEW: 44 Å, 0.01
- PC1 (60 Å): old = 61 Å, 0.01 => NEW: 62.1 Å, 0.02
- PC2 (100 Å): old = 95.2 Å, 0.013 => NEW: 98.5 Å, 0.033
- PC3 (200 Å): old = 200 Å, 0.01 => NEW: 204 Å, 0.04

Comments and additional data from other labs are more than welcome!

Julien

[John Donovan]

Thank-you Julien. I will send this to our colleague.