DEPARTMENT OF PHYSICS

INDIAN INSTITUTE OF TECHNOLOGY ,GUWAHATI

By BHOLU RAM SWAMI

GUIDED : DR.D PAMU

Introduction :

Diffraction

X-ray Diffraction

Electron Diffraction

Neutron Diffraction

Basic Difference b/w x-ray ,electron and neutron diffraction

Advantages

IntroductionDiffraction : : The process by which a beam of light or other system of waves is spread out as result of passing through a narrow aperture or across an edge.

X-ray diffraction : The atomic planes of a crystal cause an incident beam of X-rays to interfere with one another as they leave the crystal. The phenomenon is called X-ray diffraction.

Electron diffraction: the diffraction of a beam of electrons by atoms or molecules, used especially for determining crystal structures.

Neutron diffraction : Neutron diffraction or elastic neutron scattering is the application of neutron scattering to the determination of the atomic and/or magnetic structure of a material

Discovery of electron diffraction

X –ray diffraction Electron diffraction Neutron diffraction

Wavelength needed forcrystal diffraction of the order of λ=1Å which is same size as an atom

Wavelength needed forcrystal diffraction of the order of λ=1Å

Wavelength needed forcrystal diffraction of the order of λ=2Å

X-ray have energy E=10^4 e V

Electrons have the energy E ̴ 40 e V

Neutrons have the energyE ̴ 0.08 e V

Graph between wavelength Vs energy

Atomic scattering power decreases as scattering angle increase.X-ray scattering amplitude is strongly dependent on sin q/lmaking it very difficult to get good quality x-ray data at high sin q/l

Atomic scattering power Decreases as increasesangle .

Atomic scattering poweris change erratically with angle .

X-ray diffraction Electron diffraction Neutron diffraction

X-ray is the cheapest the most convenient and widely used method.

Electron beam can easily produced by cathode tube ,easily available .

Neutron sources in the world are limited so neutron diffraction is a very special tool and very expensive.

X-rays interact with the spatial distribution of the valence electrons.

electrons are charged particles and interact with matter through the Coulomb forces. This means that the incident electrons feel the influence of both the positively charged atomic nuclei

neutrons are scattered by the atomic nuclei through the strong nuclear forces. In addition, the magnetic moment of neutrons is non-zero, and they are therefore also scattered by magnetic fields

X-ray diffraction Electron diffraction Neutron diffraction

Normal penetration Less penetration Highly penetration

X-rays and electrons are scattered by atomic electrons whereas neutrons are scattered by atomic nuclei. This results in a number of differences, perhaps the most important being in the scattering from light elements. Whereas one electron on a hydrogen atom can be hard to find by X-ray or electron diffraction, the hydrogen nucleus scatters neutrons strongly and is easily found in a neutron diffraction experiment.

The magnetic structure of materials is determined by neutron diffraction ,electron and x-ray diffraction doesn’t give any inform about magnetic property .

To measure the thickness of thin films and multi-layers we use only electron diffraction ,x-ray and neutron diffraction can’t.

Range of diffraction

Measurement under atomsphere pressure

XRD is Non destructive technique ,easly sample perp.

X-ray are not observed very much by air, so the speciman need not be in evacuated chamber

Probe depth controle by incidence angle

X-ray diffraction structure analysis can be applied for single crystal

All structure information is in reciprocal space we collect and measure HKL intensities ,then solve and refine a crystal structure

Crystal cell symmetry ,cell parameters can be easily extracted from electron diffraction patterns

Diffracted beam have high intensity.

Can handle nano -size crystals.

Small amount of material needed.

Crystals do not absorb neutrons ,so they are useful for studying components that contain heavy atoms that strongly absorb x-rays

Neutrons can penetrate several millimeters of materials like aluminium and steel

Neutrons are more useful than X-rays for determining the crystal structures of solids containing light elements i.e. Neutrons interact very strongly with lighter elements.

Thank you