Both are close for elemental study. But XRF is better that provides more information in-depth. Please see the link below.

https://ywcmatsci.yale.edu/gallery/xrf/principle

Best regards

Dear Jaliya Ranaweera ,

let me first summarize some facts:

i) 'thin' film containing sulfur (S) on top of gold (Au) layer

ii) S containing film:

S K-edge: 2,47keV

S fluorescence lines:

S K-alpha: 2,3keV

S K-beta: 2,46keV

iii) Au substrate:

among others;

Au MIII edge: 2,74keV

Au fluorescence lines:

Au MIIINIV: 2,39keV

Au MIIINV: 2,41keV

Data were taken from J. A. Bearden tables:

https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.39.78

Conclusions:

a) The energy position of the S K-beta line is about 50eV above the Au MIIINV line; but due to the limited energy resolution of the detector (assumed to be about 120eV) S K-beta will not be seen in the presence Au MIIINV.

b) The energy position of the S K-alpha line is about 90eV below the Au MIIINIV line; but due to the limited energy resolution of the detector (assumed to be about 120eV) will not be clearly seen in the presence Au MIIINV.

c) thus the Au lines have to be omitted or extremely minimized.

There are two ways to do this.

i) avoiding, that excitation radiation will reach the Au substrate

and/or

ii) restricting the excitation energy to below Au MIII-edge energy.

XRF scenario:

In the case of XRF, you have to have x-ray photon excitation energies of above the K-edge energy of sulfur, which is at about 2,47keV. For a significant fluorescence yield you have to go to x-ray tube voltages of well above 2,47kV, at least some 100V above. However, for the maximum photon energies of such an x-ray spectrum you will have penetration depths in the very low µm regime; thus the x-rays will also hit the Au layer beneath your thin film and will be able to excite the Au MIII core level, when the energies are above 2,74 keV.

SEM-EDX scenario:

In the case of electron excitation one will have sub micron penetration depths for the whole electron scatter cascade, when you deal with quite low primary electron energies*). The penetration depths of the primary electrons of such a beam is much smaller.

So there is a chance, that you will have only a small fraction of primary electrons, which will be able reach the Au substrate.

If one, in addition, restricts the electron beam voltage to below 2,74keV; there is no possibility to excite the Au MIII fluorescence.

Final conclusion:

a) XRF is, to my opinion, not suitable here, due to the strong S- and Au-peak overlap.

b) SEM-EDX may work, if the electron acceleration voltage is restricted to be below 2,74kV (but well above 2,47kV).

*) https://www.globalsino.com/EM/page4795.html

Good luck and

best regards

G.M.

EDS, partly because of lower acceleration voltage for the electron probe (usually 30 KeV or less), by nature, favors the lighter elements. Electron-based EDS can detect most elements, but looses sensitivity with increasing impact starting at about phosphorus (or about 2KeV in the spectral display, and higher). For XRF I am most familiar with something called micro-XRF (the X-ray tube is attached to the SEM) which, in my experience, works at about 50 KeV. The higher accelerating voltage tends to favor the heavier elements, and looses sensitivity for the lighter elements (below 2KeV). Therefore, when I have analyzed samples with both light and heavier elements, I use both probes (electron and x-ray) simultaneously, usually with the electron probe operating at 4-5 KeV. This allows the full spectrum to stand out with a more even distribution for the full elemental spectrum. That way I get the best of both techniques.

Of course, if you want quantification, your standard will need to be analyzed with both probes, and with the same operating conditions as will be used for your sample of interest. It is possible to use your investigated sample as the standard, but you will need to make it your standard with 6 or 7 analyses of the material average together to produce a single “average” Standard and input that averaged standard into your EDS software for doing your quantitive analysis.

I hope this helps. Ask questions if you need further understandarg.

Thanks Var St. Jeor ,

for going deeper into aspects with respect to electron and x-ray based fluorescence spectroscopy.

But the sample system, which is dealt by Jaliya Ranaweera , is a special one of an ill-posed fluorescence line situation.

I do not think, that by, for example, a set of 'standards' the line overlap issue of Au and S lines, as described above, can be solved. Please bear in mind, that there is a thin film containing some S on top of a layer of Au (but mainly Au, not Au as minor component or even as trace element).

Another alternative:

One might think, that total reflection-XRF (T-XRF) can do the job. X-ray penetration depths (1/e) in the angular region of total reflection can be down to around 10 to 20 A; but that is only the 1/e value. For a sufficient (large) film thickness, one might have low enough primary photon flux entering the substrate.

But there is a very strong demand on the surface quality. Only for extremely polished surfaces you will achieve the ideal reflectivities in the total reflection regime, which are described by the Fresnel equation approach.

Any surface roughness will decrease the reflectivity a bit. This (reflectivity) loss can be some % of reflectivity and is transferred into x-ray scatter from the surface, which also partly enters the substrate and thus will give rise to Au fluorescence...

Jaliya Ranaweera , you may share a bit more details of your 'thin' film, such as the estimated thickness, other elements you expect in your film, and the estimated density.

Best regards

G.M.

Jaliya: Question: Is the gold layer visible with an EDS dot map, and is the Sulfur evident with a Sulfur EDS dot map? Would that be proof enough?

Steven: Assuming Jaliya can arrange for time on a synchrotron, this may be true, but with a 10 micrometer x-ray probe, with a focused 50 micrometer probe size, I believe micro-XRF should have the resolution to detect the Sulfur K-lines by way of a Sulfur “shoulder” on the Gold M-lines.

Gerhard: Yes, I see the potential iissue between Gold M-lines and Sulfur.K-lines. However, there should be a sulfur “shoulder” present on the “SHORT Gold M-lines” (if not a peak point). I do not know if Jaliya wants quant data, he doesn’t say that. He says “proof” of Sulfur, not “quant.” It sounds like he wants to prove the Sulfur is there, not quantify the Sulfur. And a combination of EDS and Micro-XRF ”might” give him that Sulfur resolution as a Sulfur “shoulder“ on the gold M line peak. In fact, either EDS, or micro-XRF may do that alone.

I have been trying to get EDS folks to predict where the peak is for an overlap element when the shoulder is present. That way it may be possible to estimate a quantization for an overlap element (when a shoulder is present). But no luck yet, that would require some math and a data set for all the over-lapping elements.

Dear Var St. Jeor ,

you are right;

a) if the Au line (Au MIIINIV) is not very large compared to the S K alpha, one should 'see' the S-K-alpha as shoulder on the low energy side. However it depends on the energy resolution of the detector. But nevertheless, it is necessary to reduce the Au line as much as possible.

b) You are also right with respect to the quantification of S in the film. Jaliya Ranaweera , as I understand, will see, whether there is a 'presence of S' in his film, and not 'how much' yet.

When using a synchrotron as light source, as Steven Van Petegem suggested, one is easily able to prevent the Au MIIINIV line by choosing the excitation energy to be below the Au MIII edge excitation (i.e. below 2,74keV) by appropriate setting of the monochromator. Here, in the synchrotron case, there is not the necessity of having a quite broad band x-ray beam for excitation of the S K-edge. There is enough photon flux.

Best regards

and many thanks to all participants of this lively discussion;

G.M.

Gerhard Martens Var St. Jeor Steven Van Petegem and Rakibul Hassan

Dear Researchers,

Thank you very much for your time and for sharing highly technical information. As highlighted by Var St. Jeor, I just want to scientifically prove the presence of S in my thin film, not quantify. I greatly acknowledge your valuable feedback. I learned a lot.