Mian Muhammad Faisal What was the resolution of your SEM scan? It's very possible you're seeing particle groups that appear to be larger while in TEM you normally disperse nanoparticles so there dilute and your imagine individual particles. A good way that has always worked for me is compare TEM particle size with XRD analysis.

Why is particle size measured with SEM is bigger than TEM?

In a TEM, a nearly parallel beam of electrons travels through a thin specimen, and the resulting image is magnified electron-optically by a series of electromagnetic lenses, the main one of which is the objective lens. That why Particles appear ∼3% larger in the SEM than in the TEM microscope

In addition to the answers above I would like to say that it also depends on the method of sample preparation. For SEM, you mostly take power sample which has higher agglomerated particles while for TEM the particles are thoroughly dispersed in a solvent, thus reducing the particle size considerably. This results in a different measured particle size.

Hope this helps!

I appreciate the reply from Adam Weidling Saad Zahraw Sekhi and Akanksha Adaval , I would like to add that the resolution of SEM was 5 um and for the TEM results it was 100 nm.

I see some problems with your answers to the previous comments. If your SEM resolution was 5microns and TEM 100nanometers, how you were able to see 101 nm diameter particles with SEM and 6.5 nm diameter particles with TEM? The resolution in both microscopes should be much better (smaller) than the particles you are observing. Maybe what you are quoting as the resolution is just the scalebar in your images? To answer your question if you want to compare SEM and TEM directly, the images should have a similar field of view, or scalebars, otherwise, some other factors can affect the apparent size of your measured particles. Another possibility is that one of your microscopes is severely miscallibrated.

I recommend posting the two images to get additional information. Did you pre-treat the two samples before imaging? Were samples taken from the same batch? Please write details. The discrepancy you got is really significant.

Use the same TEM grid you observed in TEM for SEM observation. Compare results, they should be the same. Otherwise something is very wrong with one of your microscopes. And I would advise to read a bit about basic things in microscopy, such as resolution.

Dear Mian Muhammad Faisal

SEM gives us Morphological data; However the particle formed can be agglomerated and we are not sure about its exact diameter, it can be better if you use DLS technique in that case.

TEM gives us the internal atomic arrangement data as well high resolution projection images of a particle, obviously size will be low compared to SEM since the resolution of sample under analysis itself is in nm (thin), technically its not recommended to compare both for morphological purpose.

Please correct me if am wrong.

Thanks

In addition to the above mentioned excellent suggestions, particle size in SEM is relative and can’t be compared to TEM which is absolute and more accurate. I would go with your TEM number assuming both microscopes are well calibrated.

Would you mind posting the brand and model of TEM and SEM. Lower end microscopes are not known to yield good resolution.

Dear Chandrasekaran Nagaswami , I am sorry, but you are wrong. Both types of microscopes are giving "absolute" measurements and should give the same results for as long as specimen preparation techniques are adequate and microscopes are healthy.

The main problem for the author of question could be that his SEM is not capable to resolve nanoparticles and thus it's not suited for the work. But we have not seen pictures, so it is just a speculation.

Mian Muhammad Faisal the concept behind it is explained in this page;

https://www.thermofisher.com/in/en/home/materials-science/learning-center/applications/sem-tem-difference.html#:~:text=The%20difference%20between%20SEM%20and,sample)%20to%20create%20an%20image.

Due to the obvious generally high prospects and the projected electrons were energized to emerging in to the sample, so the TEM image shows interior structure and realistic particle sizes.

But in the case of SEM is just scanning the subjected sample area. So, In contradiction to SEM analysis, this makes studying actual particle sizes challengin and having some mismatches compared to TEM.

I think you can disperse the sample in solvent and drop cast on aluminium foil. The solvent and chemistry of the dispersion (pH, IS and particle concentration) should be identical to that of TEM drop casting method. Then try to see it in SEM after vacuum drying. Do not over dry the aluminium foil at high temperature. Best is to vacuum dry at 60 degree. That should be enough to avoid agglomeration phenomenon. Then you may get good results. In any case you won't be able to see particles as small as 5-10 nm in SEM. but you still may validate your results.

I guess it is a matter of resolution under the set zoom in case of SEM. The image could demonstrate the aggregates of the primary particles. Another thing, if the material is uniform or not. If not, the components of a hybrid sample can exhibit different size distribution profiles calculated from images.

Michael Nazarkovsky Thank you very much for your input.