I did XRD for a sample using powder form, and also using thin film. results showed different patterns.what does it indicate? and is it valid to use thin films although references used powder ?
Thanks in advance..
Thin films do not need to have the same Bragg peaks compared to a powder, because both typically do not have identical structures. For example, thin films are textured (i.e. they have a preferred orientation) and thus they show more pronounced peaks for one lattice plane, and all the other have substantially lowered or even absent peak intensities. And it is also possible, that powders and thin film samples have completely different structures: I remember that we once wanted to deposit anatase TiO2 thin films, but the films always had rutile structure ... So be careful with misinterpretations or expectations! Kind regards, Dirk
The standard powder XRD technique assumes a sample thickness which is sufficient to interact without any compromises with teh X-ray beam. If you do not fullfill these requirements you will get at least different intensities since for small angles the beam perhaps still interact with the sample whereas with higher Bragg angle a lot of the beam interacts with the sample holder or transmit the layer and cannot contribute to the signal. Therefore gracing incident techniques have been developed which reduces this influence. However, this geometry has other disadvantages which can be "roughly" corrected but never totally since you can never be sure that the assumptions considered are fulfilled in your specific case. Thus, as reference it is perhaps not really suitable. However, phase identification and probably also a rough estimation in case of phase mixtures might be acceptable. But at least the last is questionable if you cannot proof that the phase distribution is inhomogeneous. Thin layers also have the tendency of a strong texture so that this complicates everything...
I guess, all these effects are described in newer (because of gracing incient geometry) fundamental textbooks in a much higher quality that these few sentences.
Usually, the pattern of a thin film shows only some peaks with respect to that of a powder, however at similar peak positions.
Thin films do not need to have the same Bragg peaks compared to a powder, because both typically do not have identical structures. For example, thin films are textured (i.e. they have a preferred orientation) and thus they show more pronounced peaks for one lattice plane, and all the other have substantially lowered or even absent peak intensities. And it is also possible, that powders and thin film samples have completely different structures: I remember that we once wanted to deposit anatase TiO2 thin films, but the films always had rutile structure ... So be careful with misinterpretations or expectations! Kind regards, Dirk
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