Dear Baha, By using SEM you can not determine the surafce thickness exactly in any way.If you want to measure the exact thickness, create a step before the deposition of surface layer and after depoistion of the layer, measure that step by AFM or surface profilometer.

You need to look at the cross section of your material. You can cut your sample, mount it and then look at the cross section after polishing and etching.

You can also use FIB. There is a cross sectioning function in FIB microscopes using which in situ observation of cross sectioning and coatings is possible. If the coatings are too thin, again you can cut a TEM sample using FIB. You need to be very careful during TEM sample preparation so that the area covered by the coatings is not milled. 

Once you observed the coatings you can measure their thicknesses.

Hope this helps.

Cheers,

Ahmad

Dear Baha

If you don't care about imaging the thickness of the coated layer, therefore, you can use an Eddy current method such as Posi Tector 6000, made by Defelsko, Rchmond, ON, Canada.

Electron microscopy only shows the electron dense part of a particle and does not show a surfactant layer. If your particles are small you can compare the hydrodynamic size from DLS (which shows the influence of the surfactant layer) with the electron microcopy measurements.  I suspect too that the contrast in electron microscopy will be poor due to the low molecular mass constituents.  However, ammonium nitrate is highly soluble in water, so a suitable carrying liquid (ethanol?) may be a problem. You may wish to estimate your coverage by a knowledge of the surface area and the amount of surfactant you have in the system per unit surface area.  Also note that ammonium nitrate is a vigorous oxidizing agent and, when mixed with inappropriate other materials, can produce an explosive situation.  I am not familiar with the Eddy current method so cannot comment on this aspect although I'm not sure whether the technique would work on a powder - I believe that the Eddy current technique is for thin films such as paints and coatings.on surfaces.

If the thickness is at least 0.5µm and the reafractive index of the coating is known, then FTIR can be a valuable tool for thickness determination, since this information can then be determined from the Fabry Perot interference fringes created by the layer.

Hi Michael.  Will this technique also work for a powder?  If so then do we then get an average coating thickness number?

No it would not. You would need a homogeneous layer thickness with smooth surfaces.

Hi Michael  That's what I suspected. The same applies to Eddy current instruments too.  I suspect that the NH4NO3 is in powder form but we haven't heard from the poster since he posted his query.

Dear Baha, By using SEM you can not determine the surafce thickness exactly in any way.If you want to measure the exact thickness, create a step before the deposition of surface layer and after depoistion of the layer, measure that step by AFM or surface profilometer.

3 days, 9 answers, and we still do not know the form of the ammonium nitrate - is Baha actually interested in having an answer?  I will unfollow this question now.

Dear researchers thank you very much for your suggestions to solve this problem.

Dear/ Alan Rawle I'm   late for reply because I want check the suggestions by doing possible experiment to achieve my target (Know the thickness of coating layer) 

Dear/ Khaled J. Habib your suggestion used Posi Tector 6000 to determine thickness of coating layer!

Impossible because this used for coating thickness for all metal substrates and here my substrate is ammonium nitrate 

Dear Baha/Dear All

Providing a photographic image of your ambiguous sample would help us all to figure out what the best method is in order to measure the thickness of the coated layer.

I want determine the coating thickness like picture attached for substrate ammonium nitrate NH4NO3 coated with surfactant materials (cetylcalcohol (C16H34O) or stearic acid (C18H36O2)) the particles size of Ammonium nitrate (80-140 mesh)