When I try to get the XRD pattern of silver chalcogenide quantum dots, I end up with only few recognizable peaks. Is there any specific reason (like the source of X-ray) responsible for it? I use Cu K alpha for X-ray source and my QDs are in a polymer matrix.
There can be 3 main problem why you can't see your peak at XRD experiments.
1) The concentration of your Silver calcogenide NP is small. Concentrations below 5 per cent are not easy to observe by XRD.
2) your QD are not crystalline and therefore you don't have peaks.
3) The QD are very small and therefore the peaks are broad and the signal/noise ratio is low.
I agree. They Are probably too small.
They also can be not randomly distributed.
But if they are really so small (A level), just look at bragg eqation... there is no way Xray can diffract on such small structures.
As they said that might be due to small size of the particles and the nature as well. You can do TEM/SEM, then come back to XRD.
Hello Amit,
I agree with Mathias Strauss, though I really do not know the mode of your XRD measurements (like normal bulk mode or glancing angle mode used for thin films). since you have already observed some peaks and they are not for silver chalcogenide (which you have already found out, I assume), the peak you expect might be suppressed fully by polymer peaks/amorphous nature. Even though you observe a peak sometime, you can never confirm the size of QDs from broadness. XRD can not be taken as standard expt to confirm the formation of QDs. As suggested by Satyam, you have to do TEM (again not SEM). You can also try optical measurements.
Dear Ranjit
I already have done rest of the characterization but needed to know the crystalline faces of the dots, so have to depend on XRD.
One possibility is doing HRTEM (or just TEM) and analyse the electron diffraction patterns, this can give you the informations you need about the crystalline faces of the dots without the use of XRD.
If you see diffraction peaks for a powder sample and they do not correspond to the polymer (usually broad maxima) then they certainly can be attributed to your quantum dots. Their position can be different from those of silver chalcogenide as small crystallites can sometimes show a size driven polymorphism and often display slight deviation from the Bragg Law (the peak shifts are small). Generally if a mass fraction of your QD in polimer is good enough you may do good s/n measurement, try to subtract the polymer pattern and treat the difference via methods like Radial Distribution Function analysis. That will give you insight into short range order within your QT and help to guess the structure.
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