X-Ray Spectroscopy - Science method

Dear @Sangram Keshari Mohanty,

To obtain the data values for a Halder-Wagner plot or a Williamson-Hall plot after performing Rietveld refinement in PDXL2 software, follow these steps:

1. Perform Rietveld Refinement:

Complete the Rietveld refinement in PDXL2 using your powder XRD data. Ensure the refinement provides accurate peak profile parameters, as these are essential for strain and crystallite size analysis in the subsequent steps.

2. Extract Peak Broadening Parameters:

After Rietveld refinement, look for peak broadening parameters such as FWHM (Full Width at Half Maximum) or integral breadth of each peak. These values are critical for both Halder-Wagner and Williamson-Hall analyses.

In PDXL2, go to the "Results" section to find refined values for each peak.

3. Identify and Note Reflection Angles (2θ) and Broadening Values:

Record the 2θ values and corresponding peak broadening values for each diffraction peak. PDXL2 typically provides these in the peak list or profile fit results.

4. Calculate Williamson-Hall Plot Data:

For a Williamson-Hall plot:Calculate the strain (ε) and crystallite size (D) using the equation:

βcos⁡θ = kλ/D + 4ϵsin⁡θ

where β is the peak broadening, θ is the Bragg angle, k is a constant (usually 0.9), and λ is the wavelength of the X-ray source.

Plot β cos θ versus 4 sin θ using the extracted data.

5. Calculate Halder-Wagner Plot Data:

For a Halder-Wagner plot:Use the equation:

β²cos⁡²θ/sin⁡θ = k²λ²/D² + ϵ² sin⁡θ

which separates strain and crystallite size contributions more effectively than the Williamson-Hall method.

Calculate values for β²cos⁡²θ/sin⁡θ and sin⁡θ.

6. Export or Record Data:

To export data from PDXL2:Go to File > Export > Data and select the relevant parameters if the software allows.

Alternatively, manually record each 2θ, β, β cos θ, 4 sin θ, or β²cos⁡²θ/sin⁡θ values for plotting.

7. Plotting:

Use software like Excel or Origin to generate the Halder-Wagner or Williamson-Hall plots by inputting the calculated data.

These plots help in assessing the microstrain and crystallite size of materials by analyzing the slope and intercept of the linear fit to the data.

EDS, XRF, RBS, SIMS ... can be used for Fe analysis in soda lime glass.

does the shoulder appear in the total energy peak in the HPGe gamma spectrum of certain samples, there are two probabilities, if the problem in the HPGE detector, adjust it if not it is problem due to the high activity of the sample therefore it is necessary to remove the sample at the level of the detector to eliminate the peak sum phonomene

Thanks, Gerhard Martens it was indeed insightful

I have one more case where relatively good data (up to k=14) gives the following fitting (see attached).

it still show a huge error bar? can it be solved somehow?

Thanking you,

Fluorescence: After absorbing an X-Ray photon, the substance reemits a characteristic X-ray photon again (no ionization, works basically like "normal" UV-Vis fluorescence).

Auger: The X-Ray absorption leads to photoemission of a core electron (could be seen with XPS). A lesser bound electron, often from the valence shell, fills the core state vacancy. This process sets free energy that leads to emission of another electron. Example:

C KLL Auger means: a K-shell (1s orbital) electron was emitted in the first step. An L-shell electron filled the K-shell vacancy. This lead to the emission of another L-shell electron. Since the L-shell is also the valence shell of carbon, this process is also named KVV in some tables.

I think the best advice would be to contact the manufacturer. They should be able to send you the documentation you need, or if they're good, even diagnose what's going on remotely, or help you navigate through the software.

Link will be helpful to smooth XRD data by removing signal noise using origin

Thanks Ulf.......I need to calculate simulated X-ray absorption spectrum of benzimidazole derivative

I'd make a special test specimen to check homogeneity. Mill, mix, sinter, cut, polish, examine with EDS. If oxides are of different elements, you can get good results. For oxides of the same element EDS is not the best method.

Excuse me, whether I can convert the LA-ICP-MS data(ppm) to apfu (atoms per formula unit)?

Dear Rajagopalan

After of several years of experience applying TXRF spectroscopy, a variant of ED-XRF spectrometry, to the analysis of all kinds of matrixes, including dopant elements in stoichiometric materials, I believe that the lower source of uncertainty for dopant quantification is the technique used in the evaluation. In general and today, all types of analytical instrumentation of ED-XRF are robust and confidence. Nevertheless, the higher source of uncertainty that I have found in all the cases were first the sample homogeneity that is, segregation of the element in the solid sampled synthetized and second, the sample preparation for the ED-XRF instrumentation used and of course, the correct calibration of the system. Good luck.

adding to Erik's answer. The electronics of the detector must be designed to collect the electrons from a single photon. The detector and electronic system has a rate limit on collecting and forming the electron pulse. The photon rate striking the detector must be lower than the rate limit of the detector and electronics. The higher the photon rate the more pulse pile up and summing. A too high photon rate will render the system useless for both energy and intensity.

Dear Yen-Chun Chen,

your issue is a matter of the time scale of the incoming photons.

Imagine that you have got ‚only‘ 1 photon for example in 1 sec.

Here the detector has enough time to collect the charges and to provide a voltage signal in the form of a voltage peak. The shaping time of the detector’s circuitry governs the width of the peak. Its height is proportional to your number N = E_hv / E_eh given above by you.

So far all things are ok.

But now the intensity comes into play.

Having increasing photon intensity falling onto the detector the time distance between two successive photons more and more decreases down to that point when two photons interact with the detector within the shaping time of the detector.

In the worst case now the electric charges arising from absorption of two photon are collected and the voltage peak height will be proportional to the sum N1+N2 of the two charge clouds. This effect is called ‚pile-up‘. However due to the statistical distribution of the photon time distances in the x-ray beam the fraction of voltage peaks suffering from pile-up is quite small. But for increasing intensity the amount of pile-up events increases nonlinearily.

For sufficient ‚high‘ photon intensity even three-photon pile-up events may show up.

In a peaky x-ray spectrum (e. g. from x-ray fluorescence or gammas from radio nuclides) pile-up shows up when sum peaks in addition to XRF or gamma peaks are popping up. Sum peaks have got the an energy position which is equal to the sum of the photon energies of the involved photons (double or even triple photon coincidence).

In countinous x-ray spectra arising from an x-ray tube, pile-up artifacts are seen as an up-coming photon background beyond the kV limit of the x-ray spectrum. In the ideal case(i.e. no pile up) only a very few counts are showing up from surrounding radio-activity and radiation from space.

The background is produced by multiple scattering inside the sample and is not uniform for all the energies (in fact, it can be even peaked in certain regions, for instance in correspondence with the scattering peaks or in their neighborhood). The presence of an absorption edge means that the sample absorbs more in correspondence with its energy which reduces the emission. However, to see this your detector should have a great resolution and the sample should not emit characteristic lines associated to the absorption edge. In other words, you could see this with low Z samples, far from scattering peaks, and extremely good detectors if your measurement is energy dispersive.

Dear Jean,

x-ray applications  always suffer from low net x-ray flux at the detector. So it is obvious that the strongest  fluorescence line is taken for the XRD  measurements. For the case of Cu anode the flux ratio of Cu K-beta (1+3) to K-alpha(1+2) is about 0,14.

Unfortunately not only the K-alpha radiation contributes to the XRD pattern but also the bremskontinuum  of the x-ray spectrum.

The bremskontinuum will lead to a continuous background of the diffractograms.  So also here it it advantageous to use K-alpha because of its higher flux compared to K-beta.

Some more aspects (e.g. different anode material and K-beta blocking)  of this topic are given in the answers of a similar question here on RG some time ago. 

As I know, MCNP code (if you mean it) normalize the data in source description. Output data in any tally will normalized by one source particle by default (if you dont multiply on any constants).

yttrium oxide, Y2O3, has at least a couple of polymorphs; cubic and monoclinic symmetry. You should be able to check the symmetry of these within the software. Otherwise it may be as suggested above by Vladimir that multiple entries of the same symmetry have  been entered. Even oxides of the same symmetry can have varied unit cell values depending on how they've been fabricated.

When working with X-ray tube excitation and analyzing crystalline samples, diffraction peaks (Bragg peaks) can occur in the XRF spectrum. These are in principle the diffraction peaks from XRD, though difficult to calculate and predict. To my knowledge there is no commercial software which includes these peaks. Monte-Carlo methods should be best adapted for such calculations.

I'm not so sure about HSP V 2.0. But to do determine the amorphous phase if you know all the crystalline phases is by spiking method; add known wt% of crystalline material (not in the specimen candidates), do the quantitative analysis, change the refinement wt% of the crystalline material by its true wt%, in v3 u'll get the amorphous wt%. Or you can do POCNKS : "Quantification of phases with partial or no known crystal structure“ Nicola V.Y. Scarlett and Ian C. Madsen, Powder Diffraction (2006) Vol. 21(4), p. 278 – 284. doi.org/10.1154/1.2362855

Please refer to earlier question answered previously by Shankaran Sir (suggested above by Gerhard Martens as well): The links are:

He has already described two methods to estimate the x-rays output or dose. See equation 1-8; quoted by him. 

Its a excellent reply describing the facts from basics.

Dear Ian,

Many thanks for your consideration.

Best,

Zahed.

here's one page of the book I find by googling the multiple electron diffraction. It is an example of symmetrically forbidden reflections shows up in ED at certain condition.

I'm sure  you can find detailed discussion in any TEM textbook.

See reference:

The variation can have multiple reasons

a. statistics is not high enough and variation stays within the statistical error of the counts of the spectra (should cause small variations in the few % range)

solution: acquire longer to reach higher statistics so that variance disappear

b.  sample is inhomogeneous in composition and the effect is real.

solution : Acquire a map to document variation over a big field of view

c. Sample degrades under the beam ( contamination or bema damage can lead to loss or gain in signal of elements due to absorption or simply loss of oxygen or other light elements.

Solution : reduce dose to avoid damage or clean sample to avoid contamination

d. Geometric effects of collection:  A rough surfaces can lead to shadowing towards the detector, which leads to differences (especially the light x-rays are absorbed by the sample)

Solution : Polish sample to make it flat

e. Crystallographic effects or channeling. When the electron beam hits the sample in a crystallographic main zone axis the electron distribution in the sample can be inhomogeneous so that different atomic columns are illuminated unevenly, leading to chemical variation compared to a spectrum taken far away form the zone axis.

Solution : Try to stay away for zone axis by tilting

F. wrong background fitting parameters set-up in SW leading to wrong fitting of spectra leading to wrong intensity determination of the characteristic peaks and then for a wrong quantification.

solution : Check for manual which mode is recommended and change parameters accordingly

It depends on what are you looking for by using XRD analysis. Also depend XRD equipment that you are using. Powder XRD can be one option, but it seems you had trouble of preparing the sample. If you need to prepare a flat surface sample, you can depose them or make the fiber sheet or simply compress them flat for a quick test.

Hope this will help

Vegards rule is a rule and no law. There are several mixtures which do not match to a simple linear interpolation between two constituents. One famous example is Au-Ag. In case of Cu and Ni it seems to be not critical.... see the attached link, however I have to admit that if you take the shown diagram and add the lattice parameter of Ni = 3.524A, the derived slope in the diagram will finally end in a lattice parameter for Ni which is considerably smaller than the correct one. Therefore, it might be that there is also a small deviation from vegards rule. I would suggest to look for some experimental data. Look e.g. the attached pdf. 

or the last reference.

may be due to coarser crystal size or thick flakes

Your question is unfortunately not fully complete. If the emission rate or fluence of a neutron source is known, we can calculate the same value at any distance using inverse square law. For the neutron sources mentioned by you, the fluence-to-dose equivalent conversion at a distance, d , can be computed using conversion factors for the particular neutron energy: Please refer to: NRC:10CFR 20.1004. Let me give you some values: For Am-Be, average energy of neutrons is 4.46 MeV and for Cf-252, average energy is 2.14 MeV and the corresponding fluence-to-dose equivalent factors are: Am-Be (QF=8.5): 1 rem = 24 x 10⁶ n/cm² and for Cf-252(QF=10); 1 rem = 28 x 10⁶ n/cm². The maximum permissible dose equivalent for a radiation worker is 20mSv/year or about 1mrem/hour (1 year = 52 weeks, 1 week = 40 working hours). From these values, you can work out whether, at the distance  away from the source you normally work, the dose is within the permissible limit. Otherwise, working backwards, calculate the distance at which you are safe. It may be of interest for you to know that you can design a shield for your neutron source by surrounding it by a paraffin cylinder on all sides to fully thermalize the fast neutrons which, in turn, is surrounded by a cadmium cylinder to absorb the thermal neutrons. The capture gamma rays produced by cadmium can be suppressed by surrounding this assembly by a further layer of lead on all sides. The high quality factor (QF) for neutrons implies neutrons are much more hazardous than gamma rays (QF=1). Personnel monitoring neutron badges are available from regulatory authorities. 

Hope the above analysis helps. For better accuracy, the energy spectrum of neutrons should be taken into account.

You can also use IR and near-IR spectra. These methods are cheaper and often more easily applied to such samples.

Thanks Aurelio for sharing your experience. It was helpful. I actually will do my Raman today. I took the glass and glass+ sample first.

Be careful, because H you will not be able to detect using EDAX. C, O and N are also very likely not detectable with EDAX, depending on the detector type and system you use (entrance window, excitation energy, ...). Such light elements are not measureable using EDAX in a straightforward way because their fluorescence line energies are very low.

It is not the original problem of EDS but mainly experimental errors as for chemical analysis as well. In fact YOU are the most critical component... The results are correct (if we exclude software mistakes), you only need to judge them correctly. If you find carbon in your analysis, it does not mean that carbon is inside since you perhaps measure a strong C-contamination on the surface (which can be different for different materials). If you do a chemical analysis you also have to take care that you don't contaminate your sample by residuals from former analysis. Finally no technique will give you correct data when you don't understand what is going on and which requirements have to fulfill since they are assumed in the software as restraints of the applied algorithms. Therefore, absolute values are in many cases questionable whereas relative results (precision) are often more reliable.

Thus, the answer on your question is: be critical, don't believe every number shown in a software, collect your own experiences, and read (mainly old) books since there everything is often better and more fundamentally explained than in new books where they usually only refer to older publications. Try to understand the physics behind the observed processes and try to get a feeling what statistics means and how big errors can be. If somebody tells you that the registration limit of the technique is e.g. 2%, then this is frankly speaking a lie for adults. There are combinations of elements where the reliability can be clearly better than 1%, but there are also combinations where it can reach easily 30% (like for carbon). This is not EDX-specific. The same happens even for XRD. The "2% rule" for the minimum phase fraction is only correct for two phases which are clearly different in their peak positions AND which have a very similar scattering power. Fe particles in a polymer you can even register with much lower concentration of 1%. In other words, there are some rules...but these are only rules, i.e. they are acceptable in 90% of all cases. But since you do not know whether your sample belongs to the 90% or to the 10% you actually don't know anything and you are only claiming something which has some statistical worth. 

Dear Rajesh Panthi

You can get the HVL of your beam in a high purity Al or Cu according to the kV of you x-ray beam.

From the HVL, calculate the corresponding attenuation coefficient and so the effective x-ray energy can be calculated by the aid of winxcom of NIST as Heyang explain.

2.9 A would be the covalent bond length. Any possibility that 2.3-2.4 could be a mutiple bond or an ionic bond?

The formula i have written in ORIGIN LAB is this

col(C)=114.59156*asin(L2/L1*sin(0.00872664*col(A)))

In your case

L1=1.7891

L2=1.5418

I hope you have x-y data . If the data is not in x-y form first do the conversion.

Step 1:paste the x-y data in origin worksheet.Remember x axis is 2THETA in degrees(not theta , not radians).If you forget this ,you will make mistake.

step2:create two more columns in origin worksheet.Remember

column A is x axis,two theta value in wavelength L1.

column B is y axis, intensity value

step 3:Right click mouse on column C,select Set column with values.

Paste the following line

114.59156*asin(0.86177*sin(0.00872664*col(A)))

Step 4:set column C as 'X'. This is the new x axis for your 2theta .

step 5:copy and paste the values  of column 'B' into column D.Remember there is no change for y axis.(column B and D set as 'Y')

Now plot column C and D

Use XCOM from NIST: http://physics.nist.gov/PhysRefData/Xcom/html/xcom1.html. It's very simple to use.

The structure of water layers near a flat macroscopic interface can be mapped with very high resolution using synchrotron X-ray scattering methods such as X-ray reflectivity (XR or XRR). Since hard X-rays can penetrate water to some extent, this can be done in situ using specialized cells filled with water or humidified gas. Fitting XRR results to an atomic model can reveal the ordering of water layers near an interface and can also resolve the termination of a hydrophilic surface. While hydrogen atoms are not "visible" to X-rays, oxygen atoms can be resolved, and the distance between O and other heavier atoms can be used to infer the state of surface-bound O (i.e. whether it is part of a water molecule, hydroxyl group, or bulk-like species). If you're interested in water-solid interfaces, the linked paper and references therein might be a good place to start.

It's possible to measure flat liquid-liquid interfaces by similar methods, but I think this is usually done in a Langmuir trough using monolayers or bilayers of hydrophobic molecules. I'm not sure how you'd do this for hydrophilic molecules (assuming they form a homogeneous mixture with water), but perhaps you could play tricks with the density of the hydrophilic species (e.g. using heavy covalently bound halogens) to separate the species via gravity.

Hi Sukumar, In SEM-EDAX  ZnO presented 2 peaks (major Intensity peak Zn K-alpha in lower keV and minor Intensity peak Zn L-alpha in a higher keV). It means the energy used is appropriated to exclude the electron from inner shell (K-level) as a high intensity (1-3 keV) and a small quantitiy of the electron back to L-level (from higher level) by emitting energy 8 -  10 keV. Hoping this information will be useful.

Measure coincidences of X-rays and ions that have reduced their charge state by 1 unit.

I appreciate you all for your contributions.

@Gert Nolze 

I have worked a lot with microprobe (3 WDS, but no EDS), but it was 20+ years ago. Since then I am working exclusively with different systems of EDS, so no direct comparison on the same instrument from me.

You have mentioned many times that WDS requires standards, but EDS also requires the same standards, no difference here (standardless analysis is pretty unreliable). 

From physic's point of view there is no substantial difference between EDS and WDS, just different detectors with different abilities. For quantification purposes WDS is always better: much better energy/wavelength resolution, much better peak/background ratio. Energy shifts (chemical shifts) are determined by interaction of electrons with specimens, WDS is just better suited for their detection. So, both accuracy and precision are better for WDS.

So, whenever good quantification required WDS should be detector of choice.

But: WDS is a bit slower (may take 5 minutes to acquire the full spectrum when about the same quality spectrum could be acquired in 1-3 min with EDS. 

WDS is highly sensitive to topography - small changes in specimen height  can lead to significant changes of signal intensity

WDS is sensitive to.beam deflection from the center of field of view, so that maps of homogeneous material at lower magnifications (usually less than x1000) will show lower intensity at their edges (it could be corrected with software, but any software corrections a prone to errors). EDS is much better suited for everyday use, when only qualitative/semi-quantitative results are needed, and more forgiving to insufficient level of operator's training. However, with proper standards (yes, standards), EDS can provide very good quantitative results.

As Michael says freeze-drying works very well to remove water - this step you need to do anyway, rather independently of used method. The actual factor depends on water content. Be also careful, the dry organic matter especially if containing sugars and mineral salts (like fruits) will be hygroscopic. Also the XRF samples if you decide for this method (this means the sample mass will change in open air, during the measurement, sample preparation, storage, etc. especially in your climate - I suspect not quite dry :-) ) .

Mineralization can be tricky, but with your samples (low amounts of fats, mainly sugars) should go easily. I was using a wet mineralization in closed Teflon bomb, with addition of one element (that is not present in your sample) as an internal standard and analysis by TXRF. Everything worked quite well for peat samples (also organic matter, so similar).

Regarding the dry mineralisation - it should also work fine (maybe a bit slower), the difference will be for elements creating volatile oxides, like S. Personally I also prefer to work with substantial amount of liquid comparing to very tiny amount of solid ash. At the end, for XRF you would need a lot of material (ash) to make a sample...

Summarizing, I would advise one of two ways:

dry:

(freeze-)drying - milling (homogenization) - XRF sample preparation - XRF (powder or pellet, remember - sample is hygroscopic; you can also use internal standard).

wet:

(freeze-)drying - mineralization (+ internal standard addition) - wet analytical method (ICP-MS, TXRF, AES, AAS).

Thanks a lot.

Dear Nur Farahiyah,

A model calculation is done in the attached Excel Sheet. Hope this is self explanatory for you.

Good Luck!

LRK

Dear Jiawen,

it depends on what you want. If you are interested in the quantification of the different Nitrogen and Carbon species, then you should make use of the measured intensities without any additional normalization. The only correction you have to apply are the different photoionization cross sections and the transmission function of your XPS system. Check the literature for details how to do this. In any case, if you only have C and N in your sample, the related (corrected) signal intensities should add up to 100%. Then you can make a peak assignment and calculate i.e. the amount of C-N, C-C, N-O, C-O, etc bonds.

Good luck, Dirk

EDS, WDS....they all require for an exact chemical analysis a compact sample with a flat surface at a certain position (working distance). This is the fundamental condition and unfortunately often forgotten since you can of course measure everything you want in an SEM (as P. Hoenicke already pointed out). For powders your object is neither compact nor flat in the sense that you cannot exclude multiple scattering of backscattered electrons at another position. For a quantitative analysis I would recommend to infiltrate the powder by high-liquid resin or epoxy and prepare it like a compact sample. Still in this case you cannot say how thick is the grain you are investigating, but by analyzing many grains you will get an impression how repeatable your result becomes. 

(in Greeklish-alologise)

Konstantine,

Ti theleis akribws na prosomoioseis; Ti ennoeis me ton oro "nanobeam"?

Use high temperature X-ray diffractometer.

see the attached file and link below.

Thanks

Michael thank you for the interest in my question. And thank you for the article and the data

Actually, my problem is divided into two parts, the first is that I want the method to determine the crystalline fraction present in my films. The second part, I made a measurement with XRD, and I got the spectrum in attached. two peaks that I have never met in the literature for microcrystalline silicon, the first around ~ 22 °, and the third around ~ 34 °. is that these two peaks have an original or is a measurement error.

Thank you in advance.

Powder samples are not good for XPS analysis. If you make a pellet out of the powder and sinter it, it will work better. Powder particles are covered with adsorbed contaminants like carbon, oxygen etc. When it is in the form of pellet, you can remove contamination by scrapping the surface in UHV. Powder as such can not be cleaned in-situ. In any case, many people carry out XPS studies on powder samples. XPS signals are influenced by contamination. Your interpretation may be wrong if XPS is taken on powder as it is. If you have no option than doing on the powder, for usual XPS(no-monchromatic), X-ray spot size is about 5 to 10 mm, you should have enough powder to cover whole of this area. It cannot be mentioned in terms of mass, as it depends on the kind of sample you have.

As a d9 system Cu(II) exhibits Jahn-Teller-distortion in various coordination modes. Actually, the observed SP is a distorted octahedron with two axial ligand indefinitely wide departed.

Depending on the ligand field stabilazation energy (LFSE) a distinct coordination geometry is prefered in a complex. If LFSEs of two different coordination geometries are similar switching between these geometries may occur.

Energy schemes according to ligand field theory may also be helpful for understanding.   

For the past 20 years, we have obtained a CT of our prostate implants as soon as the patient is released from the recovery room, about 1 to 2 hours after the completion of the implant.  We did a study on a small group of patients followed with sequential CTs and found that the maximum prostate volume was on the first postimplant scan.  (GS Merrick et al., Influence of timing on the dosimetric analysis of transperineal ultrasound-guided, prostatic conformal brachytherapy. Radiat Oncol Investig. 1998; 6:182-190, http://www.ncbi.nlm.nih.gov/pubmed/9727878).  Furthermore, the use of dexamethasone does not prevent edema but merely postpones it.  (GS Merrick et al., Influence of prophylactic dexamethasone on edema following prostate brachytherapy. Tech Urol. 2000; 6:117-122, http://www.ncbi.nlm.nih.gov/pubmed/10798812). 

Zhe Chen and colleagues presented an excellent theoretical analysis of the extent of edema and its rate of resolution.  (Z Chen et al., Dosimetric effects of edema in permanent prostate seed implants: a rigorous solution. Int J Radiat Oncol Biol Phys. 2000; 47:1405-19, http://www.ncbi.nlm.nih.gov/pubmed/10889396). 

For a long time, we thought that edema and its detrimental effect on urinary function was primarily due to needle trauma.  Then 10 years ago we started doing transperineal mapping biopsies with over 50 cores taken from most patients.  Their urinary function returned to normal much faster than our implant patients, so we feel that most implant edema is due to radiation effects rather than trauma.  (GS Merrick et al., The morbidity of transperineal template-guided prostate mapping biopsy. BJU Int. 2008; 101:1524-1529, http://www.ncbi.nlm.nih.gov/pubmed/18325064).

Dear Yuting, X-ray absorption spectroscopy is generally associated with the creation of a photoelectron, that can be treated as an electron wave propagating through a sample, and the interaction of this photoelectron wave with neighboring atoms modifies the absorption probabilty if the energy of the incident radiation is varied in the vicinity of an absorption edge. You may in many cases directly measure this absorption coefficient by means of a transmission more experiment, however, in several situations you may not penetrate your sample and measure the transmitted intensity., for example in the case of a bulk material sample or if you are working with very low energies, for which the attenuation length in solids is very small (in the order of some 100 nm, see e.g. http://henke.lbl.gov/optical_constants/atten2.html).

In those cases, you may use different other signals, that are closely related to the absorption coefficient. For example, the X-ray fluorescence, i.e. the number of excited characteristic X-ray photons of a considered transition of an element. The fluorescence originates from the relaxation of the created core hole, and its intensity is proportional to the number of core hole, and thereby to the absorption coefficient.

Other signals are the absorbed current, the X-ray excited luminescence, the total electron yield, ... - all these quantities are directly linked to the photoabsorption process itself!

Differences in PL and FL may originate from the fact that the fluorescence is usually not site-selective, while the XEOL is, which has implifications especially for magnetic materials, or complex crystallographic structures, where different optical transitions are representative for specific sites in the crystal lattice.

For the XEOL, check the following article published in

EXAFS and Near Edge Structure III, Springer Proceedings in Physics Volume 2, 1984, pp 490-495 by J. Goulon et al.,

"X-Ray Excited Optical Luminescence (XEOL): Potentiality and Limitations for the Detection of XANES/EXAFS Excitation Spectra"

If you compare fluorescence and 

Hope this short explanation helps, Dirk

Right. The spot size is determined by your own set-up parameters (slit dimensions, the divergence in your mirror system including goniometer radius, etc.).

You can observe the spot on a fluorescent target placed as a sample when you darken your experiment room (event it is difficult). 

Yes, EDS signal can be significantly affected by crystal orientation, as the work cited by Volker Klemm clearly showed.

The reason for this stems from the anisotropy of crystal structures (i.e. different ordering scheme of matter in the crystal structure depending on the crystal orientation). Therefore, crystals with very strong differences in their structure in certain orientations as compared with others, may be affected by large differences in the production of primary X-rays generated by the impinging electron beam in EDS analysis.

Such anisotropy can also be observed in the actual crystal morphology (or crystal habit). For instance platy crystals will certainly give different results if they are analysed parallel or perpendicular to the plates. The same may occur for fibrous morphology, etc. etc.

Generally speaking, equant crystal grains with cubic structure should present the least effect.

The answer, as for many other problems with EDS quantitation resides in the use of standards of known composition, similar crystal structure and crystal orientation as your unknowns.

In order to quantify the variation you may have in response of crystal orientation, try and analyse several grains with different known orientations and compare the results with models of the crystal structure. The aim is that of understanding the physics of the electron beam interaction in terms of depth distribution of the generated X-rays and their absorption paths before they reach the detector.

Dear Tammana,

I don't know the exact number. But you can check this from  NIST XPS database from the internet. From here, you will find the value in accordance with the oxidation state of Ce in CeB6. 

Good luck!

I have to disagree slightly :-). The RIR method is actually coming from a time we did not have computers and algorithms to predict "absolute" intensities as comparison between different phases. Therefore it was required to make defined mixtures in order to see how the intensities change. But also in those days major problems exists (which are already forgotten) e.g. mainly preparation problems (homogeneisation, grain distribution, textures for different compositions etc.): Vegard's rule is a rule and only fits ideally if the conditions matches in the same way. Nothing against this approach, but it is hard to generalize, although the other way - full pattern analysis - is not the ideal one since it is "only" a mathematical approach and only considers parameters we are implementing, activating etc. And this might be wrong as well, even if R-values become dramatically better.

Regarding Murats question I have to add that the major problem is the missing information about the scattering power of your phase. If you don't know the chemistry you cannot say anything. Imagine two structure with the same unit cell, e.g. Cu and Al. The diffracted intensity of both pure phases is quite different so that also a mixture of 50-50 would show much more intensity coming from Cu than from Al. If you now imagine you wouldn't know this percentage you would certainly underestimate the Al fraction and overestimate the Cu content. But already during preparation the more heavy Cu particles could be more placed in deeper regions so that your sample actually does not shows a sufficient homogenisation since you perhaps have more Al in the top. But even in case of an ideal homogenisation the different absorption would reduce the Al content and overestimate the Cu. AND: don't underestimate the influence of H. There are many phases containing crystal water or OH groups which are known but not described in the crystal structure. E.g., for ettringite 11% of the entire scattering power is not considered during missing description of H. For the phase identification it doesn't mean anything, but for the phase fraction is is dramatical.

Therefore, it is a hard job to find reliable quantitative phase descriptions of mixtures. The annual Reynolds cup shows you how "wrong" even experienced scientist in this field can be. The majority of us even wouldn't find the correct number of phases mixed together. And: They will never work with RIR!   

Sure you can use XPS. It can see down to 0.5 atomic %, which depends somewhat on the cross-section. The only principle trouble with XPS - it's sensitive to the first 1 nm of the surface. Among other methods are Rutherford backscattering (RBS), SIMS, EDX.

Have fun!

Hi Nima,

Could you be more specific:

(1) Are you using WDXRF?

(2) Are your samples fused or just powder pellets?

(3) What quantification method you used?

Sometimes when you choose quantification in terms of oxides then all metals (detected) are theoretically taken as oxides which may not be the case...so the stoichiometry fails.

In XRF usually you detect from Na and above so there is an undetected dark matrix wherein all characteristic X-rays from especially low Z elements are attenuated and hence there should be a correction. The correction methods are different in different softwares. If you are using Fundamental Parameters where you consider that the sum of oxides is 100% it may not be so in the sample actually.

Dear James

One possibility if the flux of photons is reasonably high, is the 'pile up' phenomenon. In other words, two or more photons arriving simultaneously at the detector. This problem we have ourselves faced in bremsstrahlung spectra. These counts are spurious counts, and do not correspond actual physics. Hence there is no violation of your minimum wavelength principle ( i.e. endpoint energy). Your definition of endpoint energy is correct.

E.Strub

I understand what you are asking that there might be some distribution of fission timescale... But, it is not so.. It has got much deeper implication on the dynamics involved in that time scale... Fission timescale as mentioned by Bohr Wheeler is 10-21 sec which is not verified experimentally, measurements shows only 10-18 sec only, so it raises the question what is happening for 10^3 sec, why it got delayed?

The question is why at all we get 10-18 sec timescale...Do we understand the reason.

It is a much argued topic for decades and it is still not understandable......People bring in viscosity and argue that viscosity increases with temperature which seem quite irrelevant...It require a much better explanation...

OMG, did you mean electron diffraction or x-ray diffraction?

Dear Patrick, upon studying a few experimental studies on wedge shaped magnetic thin film samples, you will realize that average domain size and structure does in general depend on film thickness. So in oreder to have that remain the same, you will probably need to achieve changed materials properties in a clever way. For doing that you will need to understand how domain size and structure scale with thickness, spin stiffness, anisotropy and magnetization (assuming homogeneous materials, for simplicity). Probably the best starting point for getting there is the book by Hubert and Schäfer, "Magnetic Domains: The Analysis of Magnetic Microstructures", published with Springer in 1998.

As always there are limits, but in general the answer is yes. You could use XRF and measure the concentration of gold from the fluorescence light emitted from Au atoms in a well defined volume. This is a standard procedure used in many commercial XRF devices for the analysis of concentration in galvanic cells. Click the link for a picture of a sample measuring cell (http://www.helmut-fischer.com/independent/31/Accessories_XRAY.asp). For a first try you could think of sending a sample to one of our application labs or simply visit an application lab.

Cheers,

Joerg Leske