Electron Diffraction

Introduction

Electron diffraction provides similar structural information as neutron diffraction. Electron beams strongly interact with nuclei and electron diffraction is more useful than X-ray diffraction for determining proton positions. The strong interaction of electrons with matter results in a low penetration depth, and electron diffraction is done in a reflection geometry to study surfaces or thin films or in a transmission mode for films or particles that are sufficiently thin. Electron beams are easy to manipulate, detect, and focus to small spots to provide high spatial resolution, which is a major advantage compared to X-ray diffraction. Using the spatial resolution is referred to as selected-area electron diffraction (SAD).

Instrumentation

Electrons scatter from gases and electron diffraction must be performed under vacuum, usually in an electron microscope. For sufficiently thin samples, electron diffraction is performed in a transmission electron microscope (TEM) and the diffraction pattern can be viewed on a phosphor screen or recorded on film. For more experimental details see the electron microscope document.

Surface diffraction

Electron diffraction can be surface selective by using a grazing incidence geometry or by using low-energy electrons at normal incidence. These two methods are called reflection high-energy electron diffraction (RHEED) and low-energy electron diffraction (LEED). Diffraction experiments can be made with electron energies between these two cases, and these experiments are called medium-energy electron diffraction (MEED). The energies of the incident electron for these experiments are given below.

LEED	10 - 500 eV
MEED	500 eV - 10 keV
RHEED	10 - 100 keV