Hello, I am trying to figure out how Phi scans work. I know in principle that we should select different domains for the Phi scan respect to the out-of-plane domain. But I wanted to try to do the Phi scan for Si (100) diffraction for Si (100) out of plane. I got one peak at 0 degree and another at 180 degrees. Do you know why this happens? and Why the intensity is not continuous but rather sharp?
Thanks in advance.
When you do a Phi scan on a Si(100) surface, it is normal to get peaks at 0° and 180° due to crystal symmetry. This is related to the rotational symmetry of silicon's face-centered cubic structure. As you increase the Phi angle, you would expect the crystal to repeat itself at 180°, which is why I think you see peaks at 0° and 180°.
Hi Ozgun. Thank you for your answer. Then, why would I not see the peaks at 90 and 270? Also, even though the angle is slightly off, wouldn't there still be diffraction? - for example, at random 27 degree (if the crystal is oriented at 0 degree).
Very often, a waver cut normal to the [100] direction has a slight misscut. The surface normal might be something line [1 b 0] with b a small value such that the crystallographic [100] is roughly 0.2 to 1 ° off the physical normal of the waver. Thus the surface symmetry is reduced from mm4 to mm2 and you end up with just 2 reflection positions at 180° with respect to each other.
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