If you see well-defined spots on the Laue photographs then it is likely a single crystal. To make sure that it is just a single single-crystal have to orient the crystal with a crystallographic axis parallel to the X-ray beam. Then the symmetry of the crystal will be evident from the photograph. Now please get a text book on X-ray crystallography from the library and read the Laue method. If you can get the book "X-ray diffraction" by B.E. Warren, Addison Wesly (1969) then look at p. 76-77. You will see there Laue photographs in transmission and back reflection geometry. By the way X-ray diffraction was first discovered by Laue and coworkers in Munich from Laue photograph. Transmission electron microscopy (TEM) coupled with electron diffraction can also be used for checking whether your substance is a single crystal or not but the technique is more involved and interpretation is more difficult. Also you focus the the on a very small area in this technique and therefore you may think that your substance is a single crystal although it is actually a collection of small single crystal oriented randomly.

Just do the X-ray Differeraction (XRD) of your samples.

Try to take a X-ray Laue photograph from your crystal if you have this facility. In fact all crystal growth laboratory must have a Laue camera. If you find that you have a single crystal then you can also orient your crystal according to your wish.

@ Tapan sir, how does the XRD pattern look like for a single crystal? Can we a confirmation from TEM analysis?

You can find simply XRD pattren. It would be like (111), (222) and (333) etc for single crystal

Laue diffraction pattern for a single crystal will have a well orders diffraction spots, while for poly-crystalline sample you will observe different diffraction circular rings.

You can look at the diffraction pattern in a TEM, if it cointains spots then the sample being investigated is single crystal, if there're rings you have polycrystalline one, if both, then it's a mixture of both types. of course, there are some special cases, but in general, this is the thing.

If you see well-defined spots on the Laue photographs then it is likely a single crystal. To make sure that it is just a single single-crystal have to orient the crystal with a crystallographic axis parallel to the X-ray beam. Then the symmetry of the crystal will be evident from the photograph. Now please get a text book on X-ray crystallography from the library and read the Laue method. If you can get the book "X-ray diffraction" by B.E. Warren, Addison Wesly (1969) then look at p. 76-77. You will see there Laue photographs in transmission and back reflection geometry. By the way X-ray diffraction was first discovered by Laue and coworkers in Munich from Laue photograph. Transmission electron microscopy (TEM) coupled with electron diffraction can also be used for checking whether your substance is a single crystal or not but the technique is more involved and interpretation is more difficult. Also you focus the the on a very small area in this technique and therefore you may think that your substance is a single crystal although it is actually a collection of small single crystal oriented randomly.

Apart from being a very useful too for characterizing and orienting single crystals, x-ray Laue technique has now become also a very useful too for structural research. This technique is in much faster than the other x-ray diffraction technique using monochromatic radiation. Because here you satisfy the Bragg relation simultaneously for different lattice planes with different wavelengths. With the advent of image plate and CCD detectors the recoding of data have become simpler and faster. With the numerous synchrotron x-ray sources all over the world the data collection has become even more faster. Now we can even do time-resolved studies. We have developed neutron Laue diffraction technique at ILL and this has been copied in the other neutron facilities. By this technique we can study magnetic structures as well. You can read the following paper :

Temperature evolution of the magnetic structure of TbMn2O5, C. Wilkinson, P.J. Brown and T. Chatterji, Phys. Rev. B 84, 225522 (2011)

XRD is the best characterisation method for you

Depending on the crystal growth method sometimes you may have well-defined growth faces. If you see good growth faces on your sample then most probably it is a single crystal. Now if your crystal is big enough and have well defined faces then you can use reflecting goniometer to measure interfacial angles. By this method you can characterize the single crystal (if it is one) and determine the (hkl) indices of the faces and determine symmetry of the crystal. This age old was used by mineralogist very successfully. The method has described in the book:

An Introduction to Crystallography, F.C. Phillips, Longmans, Green (1956).

EBSD should be the best way to confirm. However, if you means silicon, you can use TMAH etching to see whether it is single-crystalline or poly-crystalline. The etching rate is different along different crystal directions. So you will observe colorful patterns under microscope if it is poly-Si.

If you have access to a rutherford backscattering laboratory you can gain more information from this method. You could measure for example the backscattering signal in a crystallographic channeling orientation as well as in a random orientation. In a single crystal, the channeling signal should drop to a few percent of the channeling signal (dependent on the material, channeling direction, etc...), if you have polcrystalline material, the backscattered signal should be much larger. The expected signal for an ideal crystal can be calculated,

You can learn about interstitial atoms in different positions when you test different channeling directions. The question of "single crystal" can also be asked here in terms of: How many interstitial atoms do I need to speak of an amourphous material. The answer for sure is gradual.

suggestions above are good but you may not have access to such tools. The thermal and/or electrical conductivity are usually quite different between a poly-crystal and mono-crystal. You can do a simple conductivity (electrical) test using a 4 point probe and compare to mono-crystalline materials conductivity.

To use resistivity measurement for checking a sample's crystallinity is a bit indirect to put it politely. First of all you do not what the resistivity should be to compare with. The proper method would be to measure resitivity along different directions and check whether it is different in different directions. If so then it can be a single crystal. But you are not all sure because parially oriented crystallites can mimic this behavior. If you are serius to resistivity then you must measure the resistivity in all directions and check whether you can a symmetric tensor or not. If it is a crystal you will get a nice symmetric tensor and you can even find the symmetry of the crystal. But all these are very indirect and cost you a lot of measurements. Why not do the simplest thing. Just use an X-ray diffractometer or take a Laue picture of the substance. This can be done in any X-ray laboratory in about half an hour or so depending upon your experience or the experience of the guy who helps you in X-ray diffraction measurements. All X-ray labs are usually run by experienced technicians or even good scientist who did mange to get a permanent job unfortunately.

Optical spectra are the best diagnostic tools of the structure.

@Eva: Not at all. It is the X-ray diffraction. Optical spectra are surely very useful but they cannot say much about the real structure. The optical method is good to get characteristic vibratrions of some particular bonds and also local symmetry.

Here the problem is not to determine the structure (read the question please) but to characterize the sample and find out whether it is a single crystal or it is polycrystalline. Optical speectroscopy can do it by checking polarization but is not all direct. Just a single X-ray Laue photograph will tell you whether the sample is single crystal or not.

Tapan: Yes, You are right regarding the X-ray diffraction.

Nevertheless, regarding the optical spectra, there is a basic difference between pure crystalline and non-crystalline materials in the form of the absorption edge: a typical absorption band edge of pure crystalline materials is sharply decreasing absorption band at E=E_g, (except, possibly, exciton structure below E_g), while for the polycrystalline and amorphous materials there are localized states below E_g with exponential decrease in E instead.

@Eva: Surely all effects in physical properties look sharper with single crystal, then get often smeared for polycrystalline material. This however is not always true because there may be other reasons as well. So this is a very indirect method of characterizing whether a sample is a single crystal or polycrystalline. Well if you have no X-ray laboratory at home (that must be rare I guess for a materials science lab) but you have the spectroscopic instruments then you can surely try. If your substance has a temperature induced phase transition then by measuring specific heat as a function of temperature you will see specific heat anomaly. This anomaly is sharper in single crystals and rather broad in polycrystalline sample. But this will just give an idication and not a proof.

Dear all,

I think that there are many INDIRECT techniques that may give differences between single crystals and polycrystals. Electric, magnetic, optical properties, even chemical reactivity change from mono- to polycrystals, and even different monochrystal surfaces show different properties (e.g. work functions). Thus, as Tapan mentioned, all these methods may give you a clue, but they are far away from proving a monocrystalline structure. Furthermore, e.g. electric measurements are not suited for many isolating materials (oxides), where dopants or impurities play a more prominent role than the structure - what I want to say is that one has to be very very careful if such an indirect method is applied. In conclusion, XRD or neutron diffraction, in Laue geometry at best, is the only way ...

Best regards to all, Dirk

Visual inspection is the simplest. Different crystal orientations have different reflecivity. When growing crystal you know whether you have single crystal or twinned crystal. Poly crystal is easier to notice. Take a look at solar cell made from sngle crystal and from poly crystal, You can make the difference from 10 meters away.

Sure visual observation of the faces and possibly with polarizing microscope can bring you quite far. Only you never very sure about the crystal quality, mosaic spread etc. and also such observation gives only surface information. You do not know whether the whole bulk of the crystal is as good as it appears from the surface reflexion.

To check whether a material is single crystalline or polycrystalline, X- ray diffractometer is a suitable choice. It is non-destructive and very fast tool to check crystallinity. Obtained data (intensity versus angle(2theta) can be compared with help of and JCPDS cards. You can also compare the phase with the software (that may be on that system).Yo can go through this book. http://diposit.ub.edu/dspace/bitstream/2445/32164/1/MT09%20-%20Single%20Crystal%20and%20Powder%20X-ray%20Diffraction_ed2.pdf