I am trying to calculate strain in GeSn system. From theta-2 theta XRD scan, the films turn out to be polycrystalline in nature showing three slightly shifted peaks (with different concentration of Sn) compared to pristine Ge. The shifted peaks appear to be around (111), (220) and (311) plane.
From this scan, I can calculate perpendicular spacing (d_per) and hence, perpendicular lattice constant (a_per).
Now I want to calculate, the in-plane spacing (d_para) and hence, from that correspoding in-plane lattice constant(a_para). I have tried in-plane XRD and reciprocal space mapping (RSM), however, could not get the singal (intensity is very poor).
Is there any other way (theoratical or experimental) to calculate the a_para from the normal theta-2 theta XRD scan?
Thank you.
Dear Sandeep Kumar
The best way to get a reasonable evaluation of in-plane lattice parameters would be to get a rocking curve experiment as a starting point.
At this procedure, there will be an area evaluation of your distortion distribution. You are trying to do a 2D calculation in-plane and expanding it to the c axis. You may face the same difficulty in calculating the parameters as it already happens on graphite samples, induced by texture. Here, literature checking may pay off the effort; start by getting familiar with graphite, graphene 2D calculation.
I suppose your substrate may give you a good insight into the results, evaluating the lattice mismatch between them.
In such a calculation, the stress over the surface will play a role in the peak positions. The hard part will be the separation of the phenomenons. What would be the contribution of the lattice dimension and the stress all over on your results?
As you have a set of different doping element concentrations, you may have a good idea about both parameter x stress contributions.
Best regards
WNM
Wagner Da Nova Mussel
Thank you.
As my Films (GeSn) are polycrystalline in nature. I get three peaks for a particular concentration. Does the attached procedure valid to calculate the in-plane lattice constant from normal theta/2-theta XRD scan? Or am I missing something major? Please see the attachment.
Here I assume orignal system (Ge) was cubic in nature. On incorporation of Sn into Ge, the GeSn system turns out to be tetragonal in nature.
Regards,
Sandeep
Dear Sandeep Kumar
In principle, the math is correct.
However, you are considering at least two assumptions: 1) the in-plane stress and mismatch are neglected, and 2) the tetragonal distortion is along with the c axis at out of plane. It could still be c axis in-plane in a tilted like deposited crystal.
It is ok if you have sure that it is so 1) and 2) true assumptions.
That is the reason to have a rocking curve as an auxiliary in that assumption.
If it is ok to neglect it, the calculation is straight forward.
You still have the graphite-like problem of a tiny number of peaks with high texture.
Best regards,
WNM
- Badges
- Science method
- Similar topics
- Methodology
- Crystallography
- X-ray Diffraction