TEM does not specify the number of elements. What X-ray data you mean needs to be clarified. X-ray photoelectron spectroscopy can determine the zinc content on the surface. The use of a field emission source to form a diagnostic beam allows scanning electron microscopy to visualize relief inhomogeneities within one monolayer and analyze the chemical composition of the surface using a built-in energy-dispersive analysis unit.
Thanks for your answer. From XPS, we can get the zinc content but not the atom number. From XRD, we can get the lattice parameters. I wonder if and how to calculate the Zn atom number on surface of particles from the lattice parameters.
Have you refined the structure? And do you know which atoms are replaced by Zn at the surface? And do you know which surface(s) (hkl) is/are mostly exposed in this material (I personally don't know about it)? And do you know if Zn occupies sites only at the top layer?
If you have answers to the above, then maybe the following steps can help you.
1) Calculate the area of the most common hkl plane the particle is exposed at for the unmodified material
2) Estimate the maximum possible area for the case where all the replaceable atoms are replaced by Zn (from ionic radius)
3) Use the cell parameters of the modified material to calculate the area for the same hkl.
By comparing these values, I think it would be possible to know approximately how much of the surface is covered. Unfortunately, many assumptions are made.
If there are multiple crystallographic sites that can be replaced, then maybe you need more experimental data to get the coverage for each separately.