Can spectroscopic ellipsometry help in determining the percentage composition of binary compounds e.g. ZnS, ZnO i.e. the percentage of Zn and O in ZnO?
Very interesting question Aseya. Yes, you can determine % composition but spectroscopic ellipsometry does not give you signature spectra like XPS does, so you will need to have a reference. You can control oxygen % in ZnO type material if you are sputtering it down. I have not seen anyone doing this in solution processed or solvothermal synthesis, but I may be wrong. Once you have a set of ZnO thin films with different %s of oxygen, you can get real and imaginary parts of the pseudodielectric spectra from spectroscopic ellipsometry within 1 - 5 eV region. Cross reference these data with XPS and / or Raman and you will have a standard set of reference data. Now take the unknown, and from the complex dielectric spectra, you should be able to determine the %s. Based on your sample you may need to use effective medium theory to fit the spectral data though. This process becomes even more interesting if you have a ellipsometer that can map the sample or can do variable angle spectroscopic ellipsometry.
I am sure there are some literature on binary composition analysis, not sure whether it applies to ZnO type material (I will look it up). But bottom line, I would say "yes" to your question.
Yes I do agree with Palash and for better performance one must characterize it and correlate with its nano order structural parameters, which can be measured by different techniques.
Dear GYORGY,
Yes one can go for XPS and XRF but one must understand about the system before going for XPS and XRF
XPS is in my opinion the best way to determine the composition as long as the stoichiometry on the surface is expected to be the same as in the bulk (probably not true after e.g. air exposure). The relative sensitivity factors (RSF) have to be taken into consideration and then the areas of the Zn peak and the oxygen peak can be compared. Furthermore, the signal of the Zn will show chemical shifts whether it’s bound to oxygen or not, so from that signal alone a good idea of the composition can be achieved.
As the other posters have mentioned, the use of XPS is tricky, since the interaction volume is so confined to the surface. You can use Argon sputtering to depth-profile in XPS, but this can also change the valence of the material and confuse your results.
If you might be thinking of other analysis techniques, I can suggest ion beam analysis. E.g. Rutherford backscattering. This gives you the composition and a depth profile. Microprobes even allow for lateral distributions.
Dear Marti n,
Rutherford's scattering can't be a better option because of its limitations.
Dear Dillip, such a general comment on "its limitations" is difficult to refute... Could you please be more specific?
Seems like I have missed some of the discussions in this thread. I agree with Martin, Rutherford backscattering experiment is also an excellent choice here. RBS works particularly well on oxides, particularly for composition mapping and depth profiling. So for ZnO samples RBS is a very good suggestion.
I think you can get only the volume fraction out of the spectroscopic ellipsometric values. But its depending on the model you are using in an effective media approximation. there are several models which can be used. I agree that it is usefull to use a second technique to determine the ratio as well.
Best regards
Christian
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