This is not unusual. It can happen for many reasons. For example, it can happen for amorphous sample.

You may consider it as quantum dot. Try finding some literature of quantum dot oxide particles.

Please post your image. Thank you.

5A ?... TEM please, and the composition, also any details of the synthetic procedure if its available for sharing.

Thanks

Thanks for your collaboration

This the TEM image.

Composition mainly iron oxide .

The synthetic rote is not yet optimised

I am really grateful for all you answer.

Thanks for sharing the TEM. I would here other experts opinion on particle size evaluation, bcs I am not really sure that I can distinguish 0.5nm in this scale....

waiting to hear from others as well.

Thanks again.

Best

Mohamed Hamdani I'm sorry to disappoint you in a number of regards. Everything measured on TEM is an artifact of the sample preparation and selection conditions. Your micrograph show a fused bunch of atoms and the entire particle is not even present. It probably came from microtoming a dispersion in epoxy resin or similar. This produces a size and shape distribution. See attached from A Primer of Higher Space Claude Bragdon (1903). The particles can never be this small size as you'd never confine them in any container. Work out how many atoms in 0.5 nm. The size of an iron atom is 126 pm which is 0.13 nm approximately. So you're trying to claim that the particle size is less than half an iron atom?!

Another test you should do is BET surface area. At unit density with 1 nm particles we'll expect an SSA of 6000 m2/g. At 0.5 nm our expectation is 12000 g/cm3. I have never seen a material even approaching these SSA's.

Take a look at:

May 28th, 2019 Dispersion and nanotechnology

https://www.brainshark.com/malvern/vu?pi=zHSznNgprz5chz0

and read a chapter called Characterization of nanomaterials:

Chapter Characterization of Nanomaterials

I see part only of one larger particle perhaps in the 1 - 2 micrometer (at best) region. Google 'comminution limit' and find out why your material is actually in the micron size range, not nano, if you're starting with a dry powder.

For Debasis Dhak ,

Even quantum dot has not as small size.