I developed two Mg doped ZnO thin films on glass substrate of equal thickness 200 nm. One film shows a sharp highest intensity XRD peak along (002) with broad FWHM value were as the another film shows a lower intensity XRD peak with narrowest FWHM value than the other. Based on this experimental value which film has the best crystalline quality and why the variation of XRD peak intensity and FWHM occur.
For all crystalline (or partly crystalline) samles other than powder samples perferred orientation of crystallites will affect the peak height distribution. For such a thin film as yours preferred orientation in very likely. FWHM is affected by stress and crystallite size. Stress may be present in your films. Therefore I think a decision which of your samples has got the 'best' crystalline quality cannot be made on the basis of your diffractograms.
Other colleagues may have different opinions.
So let's wait for other comments.
Sharp peak indicates the crystallinity. With the increase in FWHM the particle size is decreased. Thus my opinion is first sample indicates more crytallinity with smaller size..
Dear Atique ,
you are right: increase in FWHM is an indication for small crystallite size; but increase in FWHM also is combined with decrease of peak height (Peak integral is constant).
However in the first sample the peak is very high combined with large FWHM. This is an indication for me that strong preferred orientation may be present in that sample. So one cannot rely on peak height (or peak integral) when looking for degree of crystallinity compared to the second sample.
But some one may correct me.
@ Nasrul: have you taken a spinning sample stage to reduce preferred orientation artifacts?
Sir,
In recommendation of Atique Sir, the broad FWHM attributes to decrease particle size, henceforth, your sample 1 is highly crystalline as compared to sample 2
In general, FWHM means the distribution and size of the nano or micro crystal, the building element of the thin films.
Also, If the nano or micro crystals (often call grains or crystallite) are big then one should expect narrow FWHM, as well as higher intensity than the film, consists of smaller crystals.
I think, in your case, you mentioned contradictory results.
Also, in general, doping can cause a decrease in XRD peak intensity and increase in the FWHM value as the crystallites or grain size reduces due to the introduction of stress and hence strain.
Dear Mr. Gerhard Martens,
I prepared my sample by solgel spin coating method. Then sent that sample to the laboratory where the XRD was done. I was not present there.
Dear Nasrul,
The broadening in first diffraction pattern is due to combination of high stresses present and smaller crsytallite size than the second one . The intensity is higher in first because of strong preferred orientation in the film. The results also will depend upon the film condition, uniformity and time taken to acquire the diffract pattern. Spin coating in not the technique, which can give you a good quality film and I am not aware about the crsytallite size in the powder particles used to coat the films. You should check that too.
I believe that XRD is not the right technique to ensure better crystallinity. I suggest you to perform Raman of your samples.
Best
Ankit
Dear Nasrul,
Usually, the decrease of peak height with the increase or broadening of FWHM means the crystallite size is decreasing. You can confirm that by using Scherrer formula and Williamson-Hall plot to calculate crystallite size.
Lipika
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