Hi Joel,

Both EDS (EDX) and core-loss EELS in conjunction with STEM should work fine. EFTEM is also good.

Probably EDS would be better in terms of the sensitivity. You can refer to this work: Article Imaging and elemental mapping of biological specimens with a...

Yet, either EELS or EFTEM, would be very good if you are looking for highly-resolved spatial information.

Hi,

As Jehad wrote, both EDX and EELS are fine to perform elemental mapping in STEM.

I don't know much about EFTEM since I never worked with it, but I guess it should also do the job...

Be careful with EDX if you want to get (semi)quantitative information since this technique isn't very accurate for light elements (typically C, N, O...). Advantageously, EDX doesn't need a very thin sample (~100nm or less should be good, especially for a low density material, e.g. organic materials).

EELS is more sensitive (than EDX) with light elements, and EELS allows you to perform sensitive chemical analysis thanks to its high spectral resolution (classically 0.5 to 1eV, compared to > 100eV for EDX), with < nm scale (or less). Grossly, you should be able to collect bonding informations with elemental edges analyse (ELNES method). Since EELS needs electron - transparency, your sample should be thin enough (very thin if you want to perform quantification).

One very important parameter for (S)TEM based chemical analysis is the dose (and the dose rate), since fast electrons may induce defects in you sample (in soft materials, mainly radiolysis).

https://hal.archives-ouvertes.fr/hal-01872600

Fig 5 C shows nitrogen, phosphorus and calcium mapping in a mouse kidney nanocalcification.

(Also, with this sample, we were able to detect different types of the carbon K edge, and to distinguish between carbon from biological material (tissues, ...), embedding resin from preparation and carbon from calcifications (in CaCO3- for example), and different oxygen K edges depending on the type of calcification (calcium carbonate, apatite, ...). But it is way more work than elemental mapping.)

Clément Gay. Thank you for your answer! Looking at your paper, you were able to produce something (fig. 5) more a kin to a 'heat map' where higher concentrations of the element show up in red vs lower presented in a blue. I've tried EDX and it only pinpoints discrete points on the images and tells you if the element is there (without regards to the concentration). Is this something only EELS can do? or is it just a software issue? Also, how thin does an EELS sample need to be?

Best,

Joel

Joel Turner I think you're looking at fig 4 (which is µFTIR spectroscopy) ;-)

I was talking about the next figure :

1) profile plot of P and Ca intensity = intensity integrated profile of :

2) (Greyscale) elemental mapping of N, Ca and P in the red area in the right corner image (circular nano calcification (NC))

3) low magnification image of the tissue environment of the NC

4) magnified image of the NC

Actually (2) is kind of what your talking about (it's not a heatmap 'cause it's greyscale, but white is "high" and black is "low").

It is not **directly** related to concentration, but to edge (or peak) integrated intensity of the elements on the EEL spectrum (in some conditions, you can calculate the composition but it wasn't the purpose of this experiment).

Let me explain. With STEM-EDX or STEM-EELS, you can get a spectrum-image (called SI, or spim). This image is a datacube (so 3D) which contains an image and many spectra (one per pixel) : for example :

http://www.gatan.com/techniques/spectrum-imaging

look at the 1st fig. x and y are pixel coordinates, E is the dimension corresponding to EEL spectrum.

* In each pixel ("point of the image") you have a spectrum. *

And in each spectrum there is signal from the different elements which are present in the material (in area of the pixel). You can easily find examples of spectra on the internet.

So you can compare the intensity of, say, the peak at 400eV (N K-edge) of all the pixels (this is the greyscale map of the 2nd image fig 5 in the paper). The contrast compares the intensity of the K-edge of nitrogen of every pixel. (white = high intensity, black = low). So, if you're confident, you can say "there is more nitrogen on the left of the image than on the right". But this is just a gross approximation, because the sample has to have an constant thickness over the area you're observing, etc...

--> Spectrum-imaging should also be available for EDX, since you can form an electron probe, scan a specific area on your sample and record a (EDX) spectrum for each pixel. (The name of the numerical objects can vary... Brukers instruments use the term "Hypermap" instead of spectrum-image, for example).

--> Indeed, you can pinpoint a chosen point and record a lone spectrum. So you have an information about what is in the sample at this point. Spectrum-image recording is an automatic way to record this information for many adjacent pixels.

--> About the thickness, it depends on the accuracy you need. To get an intensity map (which cannot directly be related to concentration),

Maybe you should have the figure captions next to the images ;-). Really nice answer Clement! Appreciate it!

whats your email?

Joel

You can look at the journal version for that ;)