I have semicrystalline polymer thin films (~100 nm) deposited on ITO substrate. We expect difference in their crystallinity as we go far from the substrate surface which arose due to difference in the mechanism of growth on increasing thickness. If I want to prove it through GIXRD, will it be a reliable method to do so? There is an interesting observation with changing angle of incidence from low to high (e.g. 1⁰ to 8 ⁰). Our polymer generally shows broad diffraction peaks at ~ 5-6⁰ (100), 16⁰ (200) and 25-26⁰ (020). In my samples at low grazing angle (1⁰) I can see only one peak at ~ 16⁰. However at higher grazing angle (8 ⁰) the 6⁰ peak also appeared along with 16⁰ peak. What could be the reason of this difference in XRD pattern on changing grazing angle? Is this because at higher angle X-rays are going more into the depth of sample (layers close to the substrate surface) where we expect more crystallinity or it is just that at low angle signal is not strong due to scanning less amount of polymer which increases on increasing the angle and the signal appears strongly.
I hope that my query is understandable. Hope to get some valuable suggestions in this regard.
Thanks in advance!
The grazing angle measurements are used to investigate very-thin polycrystalline films or doing depth profiling. These measurements are performed at very low grazing angle (slightly above critical angle to 5 degrees depending on material ) As you said that in normal Theta-2Theta measurements you get three peaks. At 1degree grazing angle you are getting just one peak so you may be measuring just the film itself. As you increase the grazing angle (8 deg) you are getting one more peak at 6 degree. At this high grazing angles your x-ray beam is going into the substrates as this angle is high enough as your film is very thin. I would suggest that you do following things
1. Try collecting data at different grazing angles starting from 0.3 to 3 deg in small steps and calculate the penetration depth of x-ray beam. You can easily find literature on how to calculate this. This will give a full depth profiling.
2. Compare this data with Theta-2Theta Scan and see what different features are there. this will give you more information about any substrate contribution.
3. Last thing I am bit confused about is the positioning of your (100) peak from film which is at 5-6 deg and (200) peak which is at 16 deg. Since these peaks belong similar family of planes (100) it is highly improbable that one peak is at 5-6 deg and its second order peak at 16 deg (it should be in range 10-13 deg), Unless you have very high strain. It will be really helpful if you can post some data here then it will be easy to interpret it. Also can you please let me know about the lattice parameters of you polymers.
Best Wishes,
Nitin
Hi Rekha,
I am not an expert on grazing angle XRD, but as far as I understand the topic, your first assumption is the right one (higher grazing angle penetrates deeper into the sample > shows additional peaks of lower substrate layers).
I'm not sure about your second assumption. If you use a fixed divergence slit, the amount of sample irradiated should be almost the same at higher and lower grazing angles, because of lower angles irradiating a larger surface but not penetrating deep in the sample, while higher grazing angles irradiate a smaller surface but show deeper penetration, overall resulting in an almost constant amount of irradiated sample at higher and lower grazing angles.
At least, that's how I think it works. Please anyone, correct me if I'm wrong.
Best wishes,
Chris
The grazing angle measurements are used to investigate very-thin polycrystalline films or doing depth profiling. These measurements are performed at very low grazing angle (slightly above critical angle to 5 degrees depending on material ) As you said that in normal Theta-2Theta measurements you get three peaks. At 1degree grazing angle you are getting just one peak so you may be measuring just the film itself. As you increase the grazing angle (8 deg) you are getting one more peak at 6 degree. At this high grazing angles your x-ray beam is going into the substrates as this angle is high enough as your film is very thin. I would suggest that you do following things
1. Try collecting data at different grazing angles starting from 0.3 to 3 deg in small steps and calculate the penetration depth of x-ray beam. You can easily find literature on how to calculate this. This will give a full depth profiling.
2. Compare this data with Theta-2Theta Scan and see what different features are there. this will give you more information about any substrate contribution.
3. Last thing I am bit confused about is the positioning of your (100) peak from film which is at 5-6 deg and (200) peak which is at 16 deg. Since these peaks belong similar family of planes (100) it is highly improbable that one peak is at 5-6 deg and its second order peak at 16 deg (it should be in range 10-13 deg), Unless you have very high strain. It will be really helpful if you can post some data here then it will be easy to interpret it. Also can you please let me know about the lattice parameters of you polymers.
Best Wishes,
Nitin
If you suspect different growth mechanisms, a good approach is to take GIXRD with the sample on the xy plane and and then on the zy plane, varying the incedence angle as aforementioned. This requires an extra bit of experimental preparation, but is a feasible method if you suspect epitaxial growth.
I agree with Nitin, the position of the (200) should be at smaller angle - so probably one of the peaks is indexed in a wrong way! In order to do a proper indexing, it would be helpful to give some more information about your polymer, and eventually also to see the data, as Ravi (Cheers!) already mentioned! Best regards, Dirk
Thanks everyone for your valuable comments. I have verified the data I obtained earlier and found that all the peaks I was getting was due to my substrate even at 1degree GI. I will try at lower GI.
Thanks a lot!
Regards,
Rekha
Dear Rekha,
if you have the average elemental composition and thickness of your layer, you may calculate the penetration depth of the incident X-rays into your sample, and may thus estimate the contributions to the diffracted signal as well. From my personal experience with "soft2 matter, I think that 1° incidence angle is almost a factor 4 above the critical angle of total reflection, and thus, strong contributions from the substrate must be expected in your case. I think that you have to decrease the incidence angle to less the 0.5° to get entirely rid of substrate contributions to the measured diffractograms! Good luck, Dirk
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