I have done XRD scans of germanium that was deposited on silicon substrate and subsequently crystallized by laser annealing. In the case of theta-2-theta scan I observed a dominant substrate peak but could observe the peaks due to germanium too when I changed Y axis to log scale. In the case of grazing incidence I observed germanium peaks predominantly.
Which scan would be more accurate to calculate the crystallite size and percentage crystallinity from ?
Dear Nabasindhu Das,
'Pitfalls in the characterization of nanoporous and nanosized materials'
Check that paper out and try to adapt in your grazing incidence if you cant go ahead with 2-theta.
Another option is to do a coupled theta-2theta scan, but with a small omega offset (sample tilt) - just enough so that you don't see the substrate peaks. Usually just a couple of degrees is enough.
This is the principle behind silicon single crystal "zero background plates" for powder diffraction - the silicon is cut enough "off axis" so that in a symmetric scan no silicon peaks are observed on the detector. What I am suggesting accomplishes a similar result by using an "omega offset" sample tilt so that your silicon peaks are not seen. Because your germanium film is polycrystalline, a small omega offset should not significantly alter the XRD spectrum and these peaks show up very nicely. A "grazing incidence" scan takes this to an extreme, with the omega angle set small enough to limit the penetration of the incident beam to just the thickness of the film so that diffraction from the substrate is not observed.
the thickness of your film must be very small. a grazing angle would scan the surface therefore you get peaks form Ge film.X rays transmit to substrate in 2 theta scan and being a single crystal strong peaks dominate the peaks from the film. if you want to continue to work with films of thickness less than 100 nm, grazing angle is suitable. Thanks
To measure crystallite size, by far the most important consideration is instrument resolution. Unless you are using Seemann-Bohlin, the resolution will be much better for a theta-2theta (Bragg-Brentano) scan. Therefore use a theta-2theta scan for crystallite size measurement. If you use Andrew's suggestion (a good idea), be sure to run your standard scan with exactly the same scan conditions. Actually, whether you use an omega offset or not, be sure to run the standard scan with the same setup as your sample.
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