When electrons interact with crystalline materials, the resultant is a pattern of rings accompanied by spots, which characterise the sample. This phenomenon is referred to as electron diffraction. 

On a TEM (transmission electron microscope), electron diffraction is performed by focusing the beam down to the point that may be focused at a single particle or the edge of a giant crystal using the magnetic lenses of the beam column. The outcome is a dark picture with light dots where the beam scatters due to the crystal structure.

Meaning of Electron Diffraction

• Electron diffraction is a method for determining the crystal structure of materials. If you project an electron beam onto a specimen, the crystal lattice acts as a diffraction grating, scattering electrons in a predictable pattern and producing a diffraction pattern.

• Electron diffraction occurs due to an elastic scattering when the incident electrons do not lose their kinetic energy in their interactions with atoms.

• This electron diffraction experiment is a collective scattering phenomenon in which electrons are dispersed by atoms in a regular array (nearly elastically).

Importance of Electron Diffraction

The importance of Electron Diffraction is explained in the points below :

• Electron diffraction can be much less penetrating and scattering much more intensely than X-ray. As a result, electrons are sensitive even on fragile layer samples, resulting in a strong diffraction pattern in a short period.

• The points of light or rings in the case of an amorphous or polycrystalline material can be utilised using electron diffraction results to determine information on the crystal structure of the sample. When making core-shell nanoparticles or designing materials with medication release or absorption capabilities, crystal structure is crucial.

• As opposed to X-ray diffraction, This offers the benefit of having high-intensity diffracted electron beams with exposure periods of only a few seconds.

• One of the uses of electron diffraction methods is gas electron diffraction (GED). GED coursework is required for a thorough grasp of structural chemistry.

Type of Electron Diffraction Pattern

There are three different types of electron diffraction patterns. The formation of each is based on the different conditions of the matter such as crystal structure, thickness, etc. The single-crystal material exhibits a spot pattern or Kikuchi line or combination of both Kikuchi and spot pattern, while the PO, crystalline material shows the ring pattern.

Ring Pattern

These patterns are made due to ultrafine grains of polycrystalline materials. So, phases in various polycrystalline materials are determined by interpreting their ring patterns. Polycrystalline specimens are pure aluminium or pure gold.

Spot Pattern

There are two parameters in the spot diffraction pattern used to index and interpret such types of electron diffraction. The first is radius R, which is the difference between the diffracted and the transmitted beams in electron diffraction patterns. This distance can be considered an average vector to the plane reflection. Secondly, the angles between two vectors are drawn from the centre to two adjacent points. Each of these spots represents a set of planes.

Kikuchi Pattern

Kikuchi line patterns will happen when the material’s thickness is more than expected and almost perfect. These patterns are made by electrons scattered inelastically in small angles with a slight energy loss. Then, these beams of electrons scatter elastically and create Kikuchi lines in the pattern. Kikuchi lines in the designs are pairs of parallel dark and bright lines.

Diffraction with the different States of Matter

Electron interaction with matter

To get diffracted, electrons need matter. Their interaction differs from other radiations such as X-rays and neurons because of their negative electric charge. Negative electrons are diffracted due to Coulomb forces when they interact with a positively-charged atomic core. 

Electron diffraction happens due to an elastic scattering when the incident electrons do not lose their kinetic energy in their interactions with atoms. In some cases, however, even scattered electrons can be diffracted inelastically.

Diffraction on an atomic lattice

The wavelength of the electron beam used in a typical electron microscope is sufficiently very small such that the crystal lattice acts as a diffraction grating. Hence, a diffraction pattern can be formed with the help of beams diffracted under different angles and intensities. 

Diffraction of molecules in gases

Diffraction can be performed on individual molecules dispersed in a gaseous atmosphere. Since multiple molecules diffract the beam with different orientations, the resulting diffractogram depicts concentric rings analogically to the ring diffractogram of polycrystalline materials. 

Conclusion

We learned the meaning and importance of electron diffraction and the difference between electron diffraction, X-ray, and neurons. It gives a precise analysis of the particles. This page explains the many patterns of electron diffraction and the states of matter in which electron diffraction may be employed.

Derived experimental approaches for material characterisation are also known as electron diffraction. X-ray and neutron diffraction are related techniques.