ELECTRON DIFFRACTION

- .Scattering of electrons-S cattering intensity Vs Scattering angle

.Sumeet S Chavan .Sumeet S Chavan

MM – ( – )sc II sem III – ( – )sc II sem III

THEORY OF ELECTRON DIFFRACTION THEORY OF ELECTRON DIFFRACTION

For the single crystal x-ray diffraction studies described.

It is neccesary to have a single crystal that are atleast 0.05 mm in diameter. Otherwise, the intensities of the diffracted beams are too weak to be detected clearly.

This is because the efficiency with which x-rays are diffracted is very low.Often, however crystals of diameter as large as 0.05 mm are simply notavailable or cannot be prepared.

In such cases electron diffraction may be used. This techniques makes use of the wave properties of electrons and because of the scattering efficiency of electrons is high, small samples may be used.

Electron diffraction refers to the wave nature of electrons. However, from a technical or practical point of view, it may be regarded as a technique used to study matter by firing electrons at a sample and observing the resulting interference pattern.

Schematic figure of the electron diffraction

Figure shows the electrical connections and a schematic view of the electron gun and tube.Electrons are emitted from the cathode when it is heated by the 0-7V heater supply.The electrons are focused by the focus element and accelerated to the graphite target by the high voltage supply.After passing through the target they have sufficient energy to light up the phosphor screen when they hit it.Since, the electrons are waves, they have a wavelength λ given by the de-Broglie relation: λ = h/p

SCATTERING OF ELECTRONS

It is general physical process.

A process whereby an electron is deflected from its original trajectory as result of collision.

This scattering typically happens with solids such as metals, semiconductors and insulators and is a limiting factor in integrated circuits and transistors.

SCATTERING INTENSITY VS SCATTERING ANGLE

polar plots for electron intensity at different electron energies.

The electron beam was made to fall on surface of sample normally and the intensity of scattered electron is recorded at different angles.

The maxima at 50 degree as shown in previous figure in the scattered intensity of 54eV electrons can be interpreted as being due to constructive interference of electron waves after being diffracted by target.

Relative intensity of scattered electron as a function of scattering angle indicating maxima at angle 50 degree.

Reference –

Electron microscopy and analysis by Taylor and Francis.