People claim the XRD measurement of ~ 2-6 nm size quantum dots.
Can anybody explain the method or trick for measuring small size nanoparticle using normal XRD?
What is the trick to see the relevant XRD peaks (of small size less than 5 nm) to see the crystall planes?
For a sample of 2-6 nm QDs or any other kind of nanoparticles, the broadening of the XRD peaks is due to several converging reasons. Size broadening is one of them, but crystal defects or stress, surface contribution (more than 50% of the atoms are at the surface) are also contributing.
Therefore, although it is in principle possible to disentangling these effects by a careful series of XRD refinements, calibration of a monochromatic beam, etc, its will be possible to do it but too time-consuming.
A 'direct' alternative would be transmission electron microscopy to make a size distribution histogram and have simultaneous electron-diffraction diagnosis about the crystal lattice.
Hope this helps.
SAXS or DLS (just the size, no information about the crystal structure) would be more practical method for analysis. But if you insist on XRD, i would advise you to have look at the Grazing incidence method.
Best Regards
Kerem
XRD peaks, especially those at high 2-theta angles, will be too too broader for such small NPs or QDs and, unless careful refinement is done, the crsytallite size determined is not very reliable.
It would be better to look into the sample using TEM (for simple particle size distribution) and HRTEM if you wish to see the crystal planes and measure the interplanar distances (IPDs). Measuring the IPDs can help characterize the crystalline phase of the material. You may also obtain electron diffraction patter and index it to characterize the crystalline form of your sample.
Of course, you may use dynamic light scattering, as suggested already by Karem
Thanks Kerem and Sajjad.
Actually, before doing TEM or SAXS or DLS, I would like to see the XRD peaks relevant to 2theta. Possibly GI XRD would do.
Could you suggest for the methods (steps) for GI XRD? Because XRD equipment is handled by some technician. I have to request him for GI method.
- Goya is correct. XRD one need to be careful with other contributions, particularly strain.
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