Using a backscattered electron detector will provide you with images that exhibit compositional contrast and some depth information (a few hundred nanometers). You should be able to distinguish between core and shell and measure their dimensions.

Thank you so much Johannes. I still did not get your response clearly, can you suggest me any reported literature on this method?

Thanks,

Asim

Dear Thomas,

Thank you for elaboration. In our case major material for specific use is core material. While capping is just used to maintain properties of core material. By capping the core, the size of nanoparticles is increased. How do think if I synthesize NPs in two ways i.e. with capping and without capping? will it give the size confirmation?

Thanks,

Asim

Fe3O4 NPs (core material) and capped with CTAB (Cetyletrimethyle ammonium bromide). This the composition of my synthesized NPs dear Thomas.

AFM cannot solve this problem. Theoretically, it is possible to use a SEM in BSD mode, but the result would be not evident. TEM is more suitable in this case.

Good luck!

Thank you for your response Denis. We characterized NPs by TEM but it gave the size of material but didn't differentiate between the surfactant and core material in size.

Thanks,

Asim

Asim, could you upload some TEM pictures?

Just google "core-shell nanoparticles TEM". There are a lot of self-evident pictures.

Good luck!

I agree with Denis, good TEM image should definitely reveal what is core and what is capping layer.

Asim, you can try to use negative staining methods to solve your problem. You can find more details in this paper: Article Surprises of electron microscopic imaging of proteins and po...

TEM analysis

thank you all for your suggestions and referring the supportive tools.

thanks,

Asim

I agree with the answers here, SEM and AFM are ill-posed to answer this question. TEM also might not be the best since the CTAB molecules of the coating would be hard to see.

One option you can consider is to deposit the nanoparticles on a flat surface and analyze them with AFM. The nanoparticles should be dispersed, not making 3D aggregates. Then anneal the sample at about 90ºC or whatever temperature is needed to remove the CTAB coating without affecting the inorganic nanoparticle core. Then measure again the sample with AFM. The differences in height could be attributed to the material that was removed during heating (the CTAB shell). You may also need to perform XPS or EDX before and after in order to verify the removal of the coating.

This is a bit more troublesome but a relatively easy way.

Dear Raul thank you for your answer. I analysed samples with AFM and also quantify the content of the material through EDX. I could observe well dispersion of the particles. Would you think that the size of capping can be differentiate somehow precisely by comparing with and without capping?

Asim, sure, there should be a difference in particle size due to the capping. If you have well-dispersed nanoparticles, then that's half the job done. You need to find a region of interest with a density of nanoparticles relative large to get statistics. Mark that region carefully so that you can find exactly the same region on the sample after the thermal treatment. Look in the literature what is the minimum temperature needed to remove CTAB, anneal the sample at that temperature, then measure again with AFM.

You can compare the height histograms for before and after, you should see a difference in the peak of the size distribution that you can relate to the thickness of the capping layer.