I have Pr-3d XPS spectra of single crystal and its bulk polycrystalline sample of pyrochlore oxides, Pr2B2O7, where B = Zr, Ti or transition metal elements. Here, the oxidation state of Pr and B is 3+ and 4+, respectively.
Generally in bulk polycrystalline pyrochlore oxide sample, the two main XPS peaks centered at binding energies 933 eV and 953 eV are termed as Pr-3d5/2 and Pr-3d3/d states, respectively. The satellite peaks are located as 928 eV and 948 eV.
For single crystal, the whole Pr-3d XPS spectra shift towards higher binding energy of ~45 eV as compared to the same bulk polycrystalline pyrochlore oxide material. Now the two main peaks Pr-3d5/2 and Pr-3d3/d for single crystal are located at binding energies 978 eV and 998 eV, respectively.
I have repeated the Pr-3d XPS measurement several times on same single crystal and different single crystal also. But the result is same, i.e. huge shift in Pr-3d XPS spectra of single crystal as compared to bulk polycrystalline sample.
For other element present in the pyrochlore compound, the observed XPS spectra of single crystal is same as compared to bulk polycrystalline sample, i.e. XPS of B and O elements for both system i.e. single crystal and bulk polycrystalline are same.
I have attached the observed Pr-3d XPS spectra herewith. Please see it.
Can anyone suggest possible reason behind the huge shifting of 45 eV in Pr-3d XPS spectra of single crystal as compared to its bulk polycrystalline pyrochlore oxide material?
Since the spectrum is not only shifted, but also broadened this looks like the single crystal is a strong insulator and therefore charges strongly while the polycrystalline material seems to be so conductive that the peak ends up in a "normal" Pr position (see NIST entries).
If that is the case, the same effect should also be observed for the other components of your material. Can you verify that, maybe for the O1s peak?
I also confirm that this is a problem of charging. You should be lucky that you could record a spectrum of the single crystal. Often the charging is so strong smeared that you see only a strong background. Read the machine handbook to use the charge compensation unit (electron emitter or plasma neutralizer). The neutralizers only work well when there is no conductive path from the sample surface to the sample holder. 45 eV means that you will need higher neutralizer voltage parameters.
Dear Vinod Dwivedi
I strongly agree with the answer of professor Jürgen Weippert, the peaks of the single crystal look like an insulator. I think there such defects in the polycrystalline materials, the analysis of O 1s peaks can confirm that.
Kind regards
Thank you everyone for your answers. I agree with the possible reason of charging effect. In order to confirm the shifting of XPS spectra possibly emerges due to the "charging effect", I have measured XPS spectra of O1s (attached herewith). Generally, the normal position of O1s XPS peak is 529 eV ( Article This content has been downloaded from IOPscience. Please scr...
,Article Influence of electronic structure parameters on the electric...
). In single crystal, the O1s peak is at position 532.5 eV, showing the considerable shift of 3.5 eV as compared to bulk polycrystalline sample. The shift in O1s XPS peak (3.5 eV) is very less as compared to Pr-3d XPS peak (45 eV) . Is this scientifically acceptable? Can you provide or suggest the referenced paper of "charging effect on the XPS of Pr-3d and O-1s XPS" ?- Badges
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