Ideal single-crystal (monocrystalline) material "consists" of a one "big" crystallite (in fact the whole sample is one crystal having specific orientation with respect to a laboratory frame). The polycrystalline material consists of a large number of "small single-crystals". Of course in polycrystalline material these "small single-crystals" could have different orientations with respect to the laboratory frame (a "real" single crystal has only one). It is also possible, that all of the "small single-crystals" in polycrystalline, recorded in the XRD measurement, would have the same orientation (crystallographic texture). And in this case the XRD pattern collected for "real" single crystal (e.g. grown in [111] direction) and polycrystal (with (111) texture) will look the same. 

It is worth noticing that XRD measurement is sensitive only for the crystallites having certain crystallographic planes perpendicular to the scattering vector (parallel to sample's plane). The only one (111) peak seen in the pattern does not mean that all of the crystallites (in polycrystal) are oriented in this direction. It means that all of the crystallites which have fulfilled the diffraction conditions are aligned with (111) crystallographic planes  perpendicular to the scattering vector. In case of e.g. epitaxial single-crystal the presence of one (111) reflection means that (in ideal case) your whole sample fulfilled diffration conditions.

If you want distinguish between single crystal and polycrystallines films I suggest you to try TEM analysis or investigate the mosaicity by means of X-ray diffraction omega scan for example.

If you want to know more, please read about crystallographic texture or find the book by Mario Birkholtz about X-ray scattering analysis in case of thin films.

Cheers!

It is possible, but this is probably not the answer you are looking for.  Due to preferred orientation from XRD, it is possible to have only one peak and still be polycrystalline.  This is very unlikely.  Stephen R. Byrn, Ralph R. Pfeiffer, and Joseph G. Stowell, Solid-State Chemistry of Drugs.  Run a simple test like Linkam Hot Stage, to observe if there is more than one thermal event (multiple melts).

Yes, of course, it is possible. It suggests that you have a material with strong (111) crystallographic texture. Besides the (111) peak the ofher reflections such as (222) or (333) should be seen. However, having only XRD pattern, it is very hard (or even impossible) to distinguish the highly (111)-textured polycrystalline material from e.g. epitaxial thin film grown in the same crystallographic direction, since it will give the same pattern with the same set of diffraction peaks.   

Thanks for the answers.. !

So, having only one very strong peak, doesn't meant that it is mono crystalline. 

Thanks

In other words, is having one orientation as (111) synonym of monocrystaline? 

Or the could the term polycrystalline be understood as having more than one crystal with the same orientation?

Sorry for my lack of knowledment..

Could you review these terms?  Polymorphism and cocrystallization.  I need to know if you are seeing more than one crystalline form of the same compound or a crystalline structure that consists of two or more components that form a unique crystalline structure having unique properties.

I have one sputtered film of Pt with with very intense prominent (111) peak

It does mean that it is mono crystalline?

In other words, what exactly mean polycrystalline?? is in relation of the number of grains(the grain size of my sample measured with AFM is around 100 nm) with the same orientation? or polycrystalline means that you need to have different orientations? (i.e (100, (111))

Ideal single-crystal (monocrystalline) material "consists" of a one "big" crystallite (in fact the whole sample is one crystal having specific orientation with respect to a laboratory frame). The polycrystalline material consists of a large number of "small single-crystals". Of course in polycrystalline material these "small single-crystals" could have different orientations with respect to the laboratory frame (a "real" single crystal has only one). It is also possible, that all of the "small single-crystals" in polycrystalline, recorded in the XRD measurement, would have the same orientation (crystallographic texture). And in this case the XRD pattern collected for "real" single crystal (e.g. grown in [111] direction) and polycrystal (with (111) texture) will look the same. 

It is worth noticing that XRD measurement is sensitive only for the crystallites having certain crystallographic planes perpendicular to the scattering vector (parallel to sample's plane). The only one (111) peak seen in the pattern does not mean that all of the crystallites (in polycrystal) are oriented in this direction. It means that all of the crystallites which have fulfilled the diffraction conditions are aligned with (111) crystallographic planes  perpendicular to the scattering vector. In case of e.g. epitaxial single-crystal the presence of one (111) reflection means that (in ideal case) your whole sample fulfilled diffration conditions.

If you want distinguish between single crystal and polycrystallines films I suggest you to try TEM analysis or investigate the mosaicity by means of X-ray diffraction omega scan for example.

If you want to know more, please read about crystallographic texture or find the book by Mario Birkholtz about X-ray scattering analysis in case of thin films.

Cheers!

In addition to Dr. Perzanowski's good explanation: if it is important to verify that this is indeed a poly-crystalline film (I find it hard to believe that at room temperature you'd get a single crystalline film) - you can look for an in-plane peak, meaning, a peak with a momentum vector that is not perpendicular to the surface of the sample. Once this peak is measured, you can set your diffractometer on its maximum and rotate the sample in-plane. This procedure is called a phi-scan. For a single crystal you will observe distinct peaks in phi (according to the crystal symmetry). For a complete random in-plane orientation the intensity would be independent of phi, or there could be some preferential in-plane orientation which would look like a single crystal but with several repetitions at a constant phase. 

Pt is known for (111) preferred orientation. We observed that with e-beam deposited Pt.

See Table IV here: http://liork.commons.yale.edu/files/2012/11/PhysRevB.86.125305.pdf

Thank you v very much for all the kind clarifications.

It has been very helpful.

Merce

With regard to the comments given about homologous peaks (111), (222), (333),... please be aware that depending on the crystal symmetry, some of these higher index diffraction peaks are forbidden (i.e. they have a structure factor = 0). This is the case e.g. for the Si crystal structure, where the (222) reflection has a vanishing structure factor, but the (111), (333) and (444) are present. Best regards to all, Dirk

Dr. Pacios,

Based on what you wrote (reproduced at end of this post), your material is polycrystalline.  When you have more than one grains of crystals in a single mass of sample, then that is a polycrystalline material.  

Maybe a well-known illustrative example (at least to technically oriented folks such as ourselves in this forum!) would be silicon crystals.  You need a large single crystal of silicon to make microprocessors, but you really just need polycrystalline silicon to make photovoltaic ("solar") cells.  There's a picture comparing the two on wikimedia (link attached).

> the grain size of my sample measured with AFM is around 100 nm

http://upload.wikimedia.org/wikipedia/commons/7/71/Comparison_solar_cell_poly-Si_vs_mono-Si.png

check the attached file

http://nanolab.usc.edu/assets/001/87219.pdf