Hello,
I'm studying the process of organic crystal formation on surfaces. I performed XRD to an organic thin film in two modes: Bragg Brentano and PB (parallel beam). The patterns I obtained are different. As I understand it, the above results indicate that parallel to the surface I have some preferred orientation, and another orientation along the crystallites not parallel to the surface.
I would appreciate any contribution to the above topic including valuable references that would show some similar examples.
Thanks for your help,
Olga
Hello Olga, can you please show your data so we can see how different the scans are? Also it would help to know details of the slit systems, monochromators and detectors used in the two experiments. How thin is your organic film? What substrate are you using? I don't think the two modes would necessarily show preferred orientation effects differently. Parallel beam mode has advantages when looking at rough surfaces. and is more forgiving of sample displacement errors. Presumably if you have organic crystals the sample transparency error will be present, this will be more pronounced in Bragg-Bretano than in parallel beam mode.
As for my knowledge, PB mode is more preferable for thin films characterisation. Sometimes XRD detects extra peaks (peaks of weak intensities) if you used PB mode and not in BB mode.
Have you indexed all peaks that appeared in both modes and they matched any of prospective phases? I am asking because It seems like one of your XRD patterns is shifted toword higher angle by 2o (blue one).
Hello Ian,
attached file contains the XRD patterns obtained in the two different modes. The organic film is around 200nm thick and is deposited on 40 mm Si (100).
In PB mode I used a fixed angle Theta of 1 deg, with a monochromator, DivHSlit - 10mm, DivSlit - 1mm, Sct and RecSlits - open.
In BB modeDivHSlit - 10mm, RecSlit - 0.6mm
Our instrumentation - Rigaku TTRAX III
Hi Olga,
If I am not mistaken, you have 2o offset in case of Bragg mode (focused mode). If this offset is systematic you can correct it by XRD software. Another point and as Ian said " PB mode has advantages when looking at rough surfaces." i.e; surface roughness is important in case of BB mode. Do you have any information about the surface roughness of your thin film? I am asking because sometimes surface roughness can affect the peak position from mode to another. Check this technical review about Rigaku TTRAXIII same as your device (slide 5).
http://homepage.ntu.edu.tw/~kcyuan/form/For_Rigaku-Upload_powder.pdf
Hello Olga, 2 deg shift is huge!! I wasn't expecting that... Have you run a standard material under these conditions to check for alignment issues?
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