What Gerhard said makes sense! The d spacing for the 100 peak of Co(OH)2 is about 2.75 A, which is very close to 2.71 A. But we can't be 100% sure about this yet, as there is only one XRD peak here! I would suggest that Faruk should use e.g. SEM, TEM, depending on the thin film thickness, to look at the cross-section of your multilayer thin film. With the TEM, apparently Faruk you will need to prepare a cross-sectional thin section first, then run EDS and electron diffraction on an area of interest to determine what it is. If the thin film is thicker than several microns, then you could also try electron backscatter diffraction (need very good polishing prior to analysis) on the cross section. Hope this helps!

Are you using Si (100) wafer as a substrate? If so, I believe this peak is from the substrate and you have no signal from the TiO2 film at all.

No, I did not use Si (100) wafer as a substrate. I used glass as a substrate.

Dear Faruk,

during film deposition you might have got Co(OH)2 as intermediate layer(s).

Please have a look at fig. 2 of the link:

Data ADJ_ECA_Co(OH)2

The position of the 100 peak is very close to yours. The fact that only this peak pops up is most propably due to preferred orientation in that quite thin 'hydroxide layer'. But I am not specialist in that chemistry. Maybe other colleagues will comment on that.

That peak (at d=2.71 A) is not from cobalt. Nor is it from any of the TiO2 phases (rutile, anatase or brookite). How thick is your Co/TiO2 multilayer thin film? If the thickness is only several to several hundred nm, did you then run XRD at a small incidence angle (i.e. grazing incidence XRD)? Otherwise, you wouldn't be able to detect the (crystalline) thin film with XRD.

I was wondering whether that peak could be due to glass crystallisation? How did you make these samples - was it by sputtering? Did you anneal them (on glass slides?) at an elevated temperature - if so what was the annealing temperature? I think you will need to tell us more about your sample preparation (if you don't mind giving more details about your sample prep), and then hopefully someone can help you identify that specific peak.

What Gerhard said makes sense! The d spacing for the 100 peak of Co(OH)2 is about 2.75 A, which is very close to 2.71 A. But we can't be 100% sure about this yet, as there is only one XRD peak here! I would suggest that Faruk should use e.g. SEM, TEM, depending on the thin film thickness, to look at the cross-section of your multilayer thin film. With the TEM, apparently Faruk you will need to prepare a cross-sectional thin section first, then run EDS and electron diffraction on an area of interest to determine what it is. If the thin film is thicker than several microns, then you could also try electron backscatter diffraction (need very good polishing prior to analysis) on the cross section. Hope this helps!

In the given table 2theta is reported at 33.0369 and d spacing as 2.70923 A. How do you calculate at such levels of accuracy? Did you also calculate the crystallite size from this pattern? If so can it be reported (to 0.001 nm accuracy) as 48.819 nm?