When you are speaking of Raman peak it is the representation of chemical bond or phonon distribution. A peak could appear even when a material is amorphous but generally the peak is broad while it's sharp when crystalline.

Are you using a micro-Raman set-up?

If yes it could be because of the difference in area (and depth) analysis.

micro-Raman would allow measurements only on some µm^3 (depending on the objective you use...with penetration of some hundreds of nanometer depending of the laser wavelength and your thin film absorption coefficient) while XRD would be some mm^2 and probably the whole thickness of the thin film.

Basically your thin film will appear crystalline by micro-Raman while it will seem amorphous with XRD.

Apparently, the higher chamber pressure resulted in a higher degree of crystallinity in your films. To find the real reason it would be necessary to discuss other deposition parameters that may change due to the pressure increase (e.g. the higher pressure may also lead to increased substrate temperature and hence promoted diffusion of deposited atoms which CAN again lead to the formation of bigger crystallized domains, and so on).

Could you show us your data please?

What scanning method you use to get XRD data?

How thick is it? What substrate do you use?

I performed glazing incidence with omega 0.3. With same configuration I got XRD peaks for other films deposited at 0.02 mBar. I also took patterns with different omega 0.5, 0.8 etc. but results are same. Since films are 100 nm thick I am using this shallow angle measurement. Films are deposited on Silicon (intrinsic) substrate.

When you are speaking of Raman peak it is the representation of chemical bond or phonon distribution. A peak could appear even when a material is amorphous but generally the peak is broad while it's sharp when crystalline.

Are you using a micro-Raman set-up?

If yes it could be because of the difference in area (and depth) analysis.

micro-Raman would allow measurements only on some µm^3 (depending on the objective you use...with penetration of some hundreds of nanometer depending of the laser wavelength and your thin film absorption coefficient) while XRD would be some mm^2 and probably the whole thickness of the thin film.

Basically your thin film will appear crystalline by micro-Raman while it will seem amorphous with XRD.

Good question. Very insightful comments! Thanks to all contributors.

Babu! You are most likely using a conventional XRD system based on a antiquated 0D point counter system, yes? You need to at least understand your limitations with XRD in this case. Your data is "spatially blind". You have no clue about any preferred orientation, do you? Please make me eat those words Babu :-) Am I off base so far?

Please post the XRD data that you may presently have for a better feedback from the expert RG membership, as Firman suggested earlier. Do provide all the experimental details including beam conditioning, size and optics used.

I suggest a simple experiment with the sample that shows no XRD signature. Use a dental photographic film (2D recorder) to get an idea of the 2D diffraction image before you go groping in the dark with the Geiger counter:-) Jesting!

You could also continue to grope in reciprocal space with a "point source"  by rotating the sample about the "phi" axis normal to the sample surface systematically. Well of course if you are fortunate enough to have a real time 2D XRD imaging device, then you have "arrived" back into the future!

X-ray Diffraction In Crystals, Imperfect Crystals and Amorphous Bodies by Andre Guinier. 1962 - Great book! Worth acquiring for your XRD collection.

(pp. 162-163) 6.3.5. "Comparison between the Photographic and Counter Methods

It is obvious that the Geiger Counter and the ionization chamber have the advantage of precision and sensitivity. They alone permit a quantitative study of scattering. However, point by point measurements in reciprocal space are lengthy, while the photographic method gives directly a picture of the scattering in a single experiment over a large surface of reciprocal space. The resolving power of the film is excellent. Thus, sharply defined scattering regions, for example on rows or on planes of reciprocal lattice, show up very clearly on photographic film but are difficult to detect with a counter.

Let us note also that the counter is "blind". In many cases inaccuracies in the setup produce stray scattering which is easy to detect on the photographic film but which can spoil a series of experiments made with a counter.

The two methods are therefore complimentary and it would not be advisable to neglect one in favor of the other. The photographic method is admirably suited to the qualitative exploration of an unknown pattern, since one can then find totally unexpected phenomena. The counter is necessary for quantitative measurements on a pattern which is already known qualitatively."

This was printed in 1962. This has to be considered in light of the present day 2D detectors that combine the benefits of the counter & the film in one. These writings indicate some causes for the present day inertia of moving from the 0D to the modern 2D detectors. The spatial "blindness" of the 0D scintillation counter/detector is the principal reason even experienced experts using XRD are ambivalent about the 0D XRD data/results.

https://www.flickr.com/photos/85210325@N04/10515372183/in/set-72157645018820696

Thank you for the discussion

Here I am attaching the results of XRD, Raman for two different working pressure.

Hope it is clear, if not I will provide additional details

"Basically your thin film will appear crystalline by micro-Raman while it will seem amorphous with XRD". XRD trumps! :-)

BTW the low signal to noise ratio (SNR) in the 0.008mBar XRD data is a clear indication of disorder. Large defect density or amorphous component can cause similar effects as would Nano diffracting domain size, yes? I also notice some peak shifts. Is this so? Strain related?  I also suggest a higher dwell time scan for the 0.008mBar sample to improve the SNR.

Is the Si substrate polycrystalline? What grain size?

Good post Babu. You'll get even better responses now :-)

The  X-Ray can Penetrate film and reach the substrate.it's better to use soft X-ray for thin film analysis. 

Longer wavelength or lower energy will penetrate less and hence the SNR (signal to noise ratio) from the film will be a lot higher and the thin film signal will not drown in the background. That will certainly enhance resolution in reciprocal space.