Dear all,
can you please help me with a quesiton in XRD phi scan?
Let's say we have a cubic Si (111) substrate, and I choose (100) plane to do the phi scan, how many peaks can we expect to observe?
My instinct tells me there shoud be 4 peaks for a cubic structure, but in reality there is three peaks, each peak appears every 120 degrees
Dear Wenqiang Xiang ,
You are correct that a cubic structure should have four equivalent (100) planes. However, when performing a phi scan with an incident X-ray beam perpendicular to the (111) plane of a cubic Si substrate, you would only observe three peaks for the (100) plane at 120-degree intervals.
This is because the (100) planes are rotated by 45 degrees with respect to the (111) plane, so the X-ray beam will diffract from each (100) plane at a different angle, resulting in three distinct peaks in the phi scan. These peaks will be separated by 120 degrees because the (100) planes are oriented at equal angles with respect to the (111) plane.
So in summary, you should expect to observe three peaks in a phi scan of the (100) plane of a cubic Si (111) substrate, each peak appearing at 120-degree intervals.
Dear Kaushik Shandilya ,
Thank you so much for the quick response, I was still digesting your answer, phi scan is just difficult for me...
Maybe I missed something here, the angle between (100) and (111) is 54.7 degrees?
With respect to Kaushik Shandilya 's excellent answer, I would simply mention that this follows logically from the fact that for silicon, the space group is Fd3m, and the 111 axis is the 3-fold symmetry axis. Recommend you read Nye's classic book Physical Properties of Crystals.
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