Dear Soumik Kumar Kundu

You can easily take help from the following article:

Article Recent Advances in the Synthesis and Stabilization of Nickel...

metallic ferromagnetic thin films can be oxidised easily and develops antiferromagnetic NiO insulating layer. For fabricating devices using Ni layers, We always clean for NiO layer.

Traces of oxygen in the sputter gas are sufficient to oxidize the semi-Nobel metals during sputtering processes. I recommend to check the literature for this. Come back if you need more input, Dirk

Yes. I've deposited nickel thin films using ion beam sputtering and there is always a 2-3 nm thick oxide layer formed on the surface as observed from XRR analysis. However, in XRD of the films, I didn't observe any oxide phase. Maybe because I've deposited the films on room temperature. If you are working on elevated temperatures, chances are oxide phases are formed. So, your deposition conditions also play an important role in determining crystallinity of oxide layer.

Dear Soumik, thank you for asking this very interesting technical question. There have indeed been reports in the literature that thin layers of metallic nickel prepared by sputtering are quite readily oxidized. In this context please have a look e.g. at the following relevant article:

Deposition of a Nickel Film by DC Magnetron Sputtering and its Characterization

Article Deposition of a Nickel Film by DC Magnetron Sputtering and i...

This paper has been posted by the authors as public full text on RG. Thus you can freely download it as pdf file. In the last paragraph preceding the Conclusions section the authors discuss the formation of a NiO layer on top of the nickel layer. Occasionally, deliberate oxidation to form NiO thin films has also been investigated:

Rf plasma oxidation of Ni thin films sputter deposited to generate thin nickel oxide layers

Article Rf plasma oxidation of Ni thin films sputter deposited to ge...

You can easily find and access this and other useful articles by searching the "Publications" section of RG.

Good luck with your research and best wishes, Frank Edelmann

You have an oxide layer on top of non-noble metals. Often, the native oxide is amorphous and you don't see it in XRF. It takes time to organize the oxide layer, or it needs temperature. Using ellipsomety you can "see" (simulate, so the fit gets better with oxide than without) also very thin layers (from 1 nm and above).

Thank you everyone for your valuable suggestions