What happens when we rotate crystal while shooting electrons at it?

1. Jul 26, 2013

71GA

I know that if we shoot narrow beam of electrons at the crystal (we don't change the angle) we will get a diffraction of electrons according to the brag's law. Therefore we get minimums and maximums on the screen around the crystal.

Until now we have been dealing with problems where $\vartheta$ (this is an angle between an incoming beam and crystal planes) was constant. It meant that crystal wasn't rotating. To find maximums and minimums we have instead been rotating a sensor around the crystal.

But what would happen if we rotated the crystal? This would mean that we are changing the angle $\vartheta$! Would minimums and maximums move around the screen or would they only appear and disappear? What is different than before?

A good picture is worth 1000 words.

2. Jul 27, 2013

Simon Bridge

You can probably work it out just by figuring the conditions for diffraction ... start with the standard youngs interference experiment and see what happens when you rotate the plane bearing the slits.

In electron diffraction experiments, the crystal is usually thin in one direction and thick in the other two - so you get extra effects from the geometry.

3. Jul 27, 2013