# 34.9: Questions


## Quick questions

You should be able to answer these questions without too much difficulty after studying this TLP. If not, then you should go through it again!

Which of the following is not an effect of the small wavelength of the electron?

 a The angle of diffraction is very small b The reciprocal lattice points are elongated c The Ewald sphere is very large d The diffraction pattern is produced from a plane of reciprocal lattice points

B.

Why might you get a diffraction spot where you thought there would be an absence?

 a The atoms moved across a little b Inelastic scattering c Some electrons were diffracted two or more times d There is a fault in the lens

C.

Where do higher order Laue zones come from?

 a The Ewald sphere cutting parts of reciprocal lattice planes other than the one tangent to the sphere b A different scattering mechanism c Internal reflection in the microscope d Small crystals on the edge of the "single" crystal

A.

## Deeper questions

The following questions require some thought and reaching the answer may require you to think beyond the contents of this TLP.

1. If you increase the camera length, what happens to the diffraction pattern? What about the Kikuchi lines?

The diffraction spots move further apart, because the spot spacing is related to the camera length by

$r=\frac{\lambda L}{d}$

The Kikuchi lines also move further apart, and stay in the same places with respect to the diffraction spots, as they are a result of diffraction from the same crystal.

Why would it not be possible to index a zero order Laue zone in a diffraction pattern from a cubic crystal, knowing the two points 111 and 111 ?