I have deposited Cu2ZnSnS4 (CZTS or kesterite) films on Mo coated Soda Lime Glass. We have XRD data with some peaks shifted with 0.05 to 1 degree (+/-). What might be the possible cause of this and what is the value of shift acceptable?
please note amount of shift in all peaks is not uniform
One can not generalize the value. Rather you can do checking the following,
1. Strip off instrumental broadening by doing a scan with standard sample, get FWHM of it and then subtract it from your sample 2theta value ( all the JCPDS data are generally instrumental broadening corrected)
2. the in plane and out of plane stress is also a reason for peak shift. (you have to know residual stress of the sample). For thin films out of plane component is neglected.
3. If the stress is not isotropic along the in-plane (I mean x and Y axis co ordinates) that will have signature on the peak trend and shift.
So to explain the shift you may need to have this 1st hand necessary information
One can not generalize the value. Rather you can do checking the following,
1. Strip off instrumental broadening by doing a scan with standard sample, get FWHM of it and then subtract it from your sample 2theta value ( all the JCPDS data are generally instrumental broadening corrected)
2. the in plane and out of plane stress is also a reason for peak shift. (you have to know residual stress of the sample). For thin films out of plane component is neglected.
3. If the stress is not isotropic along the in-plane (I mean x and Y axis co ordinates) that will have signature on the peak trend and shift.
So to explain the shift you may need to have this 1st hand necessary information
If you are sure about the chemistry then stress is the most probable cause for large shifts. Just notice that the JCPDS is now ICDD and the cards, in your case presumably pdf 2, are not standard as no standards institute certified the values . The suggestion is always to use the phase info to simulate the pattern and of course to try measuring with some specimen tilt. If it is stress then the positions should shift. If you are not sure about the chemistry then it can also be a problem of mixed site occupancy.
You can also check other threads here to see what you can find together with CZTS in your film. Other sulfides are likely to be present with certain types synthesis
The peak shifts can arise from mainly two reasons:
1. Instrumental offset: If it is the case, the shift would be systematic i.e., all peaks will shift by almost similar magnitude. This shift can be determined easily by running a standard sample and the 2theta offset can be obtained. But I don't see any reason why you would estimate the broadening (of the standard) and subtract it from the 2theta value as @Nagaboopathy Mohan had suggested unless you want to do size determination (in which case you will also need microstrain broadening also). The broadening correction has to be given to the broadening (FWHM) not to the 2theta, when relevant.
2. Macro stress can give rise to peak shits. This would mostly depends on your growth parameters, deposition method, substrate - film relation and thickness.
p.s. While reading the JCPDS cards, select correct value of lamda (wavelength). For eg. Cu kalpha or Cu Kaverage. The associated changes are in second decimal but just in case you need to know.
I have to assume these are poly-crystalline film and substrate. What is the typical coherently reflecting domain size, in your opinion?
I also have to presume you are noticing the shift w.r.t. the other peaks from the substrate (as reference).
BTW "CZTS films on Mo coated SLG" - Please elaborate these abbreviations for us laymen. Got CZTS (CuZnSnS)! SLG - ?
My instinct would be "strain" due to lattice mismatch as the cause of the shift. Sprinkling some Graphite powder standard on the sample may help as well to confirm the shift.
guys can you please stop using the acronym JCPDS? .. check the ICDD website.. they prefer to be called ICDD
@Ravi: SLG = soda lime glass.. CZTS = Cu2ZnSnS4 kesterite/stannite
If the film is poly-crystalline, then a single conventional "powder" diffractogram may be insufficient to characterize the strain and its effect. You would certainly need to consider imaging the entire 2D diffractogram (diffraction image) to quantify any potential effects due to "preferred orientation". The use of built-in or external standards will dramatically help isolate/evaluate the effect of sample alignment and several other instrumental factors.
If film is preferentially oriented, is there any effect on peak position due to mounting of the sample? I am observing up to +/- 0.2 0 shift in the same sample characterized for the second time.
Check for specimen displacement/alignment issues... if the specimen is the same the position should remain the same
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