By clean microscope I mean the one that was not extensively used for characterization of specimens with volatile carbon compounds, and have means to prevent carbon contamination (oil free pumps, cold traps, plasma cleaning and such). Looks like your EPMA is good for your task. Easy check - to analyze carbon from the same spot for several times and see if it shows increase in C. Besides lowering kV not much can be done for improving spatial resolution.

Dear Vignesh Nallasivam,

In addition to EDS, you can perform X-ray photoelectron spectroscopy (XPS) to determine the carbon contents in low carbon steel.

Dear Vignesh,

These are two different questions, really. Are you interested in determining the (total) carbon content in steel, i.e. the chemistry, perhaps for qualifying or accepting a material? Or are you looking to measure local variations in carbon content, maybe to have some structure-property correlation? To my knowledge, no single technique can give you both those answers.

If you want total composition, then destructive chemical techniques can be used, where carbon is atomised and excited. OES as mentioned by Raghava is one such method (though not all OES systems can be used for this- eg. ICP-OES systems). Other techniques involving combustion of carbon and measurement of CO/CO2 generated. This can be done by gas chromatography or infrared techniques [1]. One more 'wet technique' is given in [2].

If you are interested in segregation, APT as you mentioned is most direct. EPMA (i.e. WDS in place of EDS) can be a less expensive choice- but certain precautions need to be taken see- [3,4].

Finally, for my understanding, why do you say, " Carbon is tricky to measure in SEM/EDS...as well as fluorescence "? I thought fluorescence is used to determine the chemical identity of an element- am I wrong?

References:

[1] http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/38/064/38064866.pdf

[2]https://pubs.acs.org/doi/abs/10.1021/ac60334a016?journalCode=ancham

[3] https://www.cambridge.org/core/journals/microscopy-and-microanalysis/article/practical-aspects-of-carbon-content-determination-in-carburized-steels-by-epma/EC2A9E73B09ADBAA652F673A1073B590

[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4949478/

As was said it all depends on your task. If you need good spatial resolution, then XPS and OEM are not good for you. SEM/EDS is not really good for carbon quantification, but suitable for comparative studies, especially when used at lower accelerating voltages, like 3-5 kV. Carbon is a common contaminant for SEM, so it is better to use clean SEM (oil free vacuum or cold trap), and WDS is better than EDS for carbon. Best spatial resolution will be from TEM-EDS-EELS and changes in composition could be easily observed, but specimens are harder to prepare, quantification is poor.

Just a reminder: even SEM/EDS/WDS resolution could be not good enough to resolve bands of ferrite and cementite in pearlite.

Dear Vladimir,

Thanks for your note. OEM and XPS are more for bulk sample. For things like local segregation, WDS in EPMA is better than EDS in SEM due to some of the artifacts SEM-EDS has like, Atomic Number Effect (Energy loss due to inelastic scattering), X-Ray Absorption Effect and X-Ray Fluorescence Effect (Hope this answer Aashranth B thoughts). This all can result in difficult to quantify and identify Carbon peak intensity from background in EDS due to its low atomic number. EDS is more qualitative than quantitative, typically for elements like Carbon. WDS measurement of C segregation in low carbon steels (

Dear Vignesh, you are a bit wrong in your analysis of EDS vs WDS.

They are basically the same techniques, share the same signal (characteristic X-rays) and have the same problems in quantification, such as atomic number effect, fluorescence, and absorption. The difference is only in X-ray detector, and here WDS is much better in detection of carbon.

APT (the same as in Atom Probe Tomography?), I believe, is very difficult to implement for your task.

TEM/EDS and SEM/EDS are useless for 0.1 Wt% changes of carbon (I thought you are interested in carbides). Clean EPMA may help.

Dear Vladimir,

I was little exaggerating WDS. Thanks for educating me on that regard. I agree, since both EDS and WDS detector shares the same characteristic X-rays generated from same interaction volume in SEM. I think WDS has better peak to back ground ratio. What do you mean by clean EPMA ? Are you referring to clean stage without hydrocarbon contamination ? or suitable calibration alloy ? or better crystal to diffract ? We are using layered dispersive element (LDE) crystals for Carbon Quantification. The interaction volume effects can be minimized by lowering the operating voltage. What else should one consider for better EPMA quantification of lower atomic number elements and low concentration elements?

By clean microscope I mean the one that was not extensively used for characterization of specimens with volatile carbon compounds, and have means to prevent carbon contamination (oil free pumps, cold traps, plasma cleaning and such). Looks like your EPMA is good for your task. Easy check - to analyze carbon from the same spot for several times and see if it shows increase in C. Besides lowering kV not much can be done for improving spatial resolution.

Perfect ! That is the best way to check. Also, I may go for longer acquisition time balancing both KV and beam current. I appreciate your valuable inputs