X-Ray Diffraction

An electromagnetic wave of high energy and very shortwavelength (between ultraviolet light and gamma rays),which is able to pass through many materials opaque tolight.

Energy : 100 eV to 100keV

Wavelength : 0.01 to 10 nanometer

X Ray

Why are x-rays used?

λ ~ Å

The process by which a beam of light or other

system of waves is spread out as a result of passing

through a narrow aperture or across an edge,

typically accompanied by interference between the

wave forms produced.

Diffraction

X Ray DiffractionA technique used to determine the atomic and molecularstructure of a crystal, in which the crystalline atoms cause abeam of incident X-rays to diffract into many specificdirections.

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

A stream of X-rays directed at a crystal diffract and scatter asthey encounter atoms. The scattered rays interfere with eachother and produce spots of different intensities that can berecorded on film.

X-ray crystallography is a tool used for identifying the atomic

and molecular structure of a crystal, in which the

crystalline atoms cause a beam of incident X-rays to diffract into

many specific directions. By measuring the angles and

intensities of these diffracted beams, acrystallographer can

produce a three-dimensional picture of the density

of electrons within the crystal. From this electron density, the

mean positions of the atoms in the crystal can be determined,

as well as their chemical bonds, their disorder and various other information.

X- Ray : X-rays absorption

UV-Far : UV- absorption (Spectrophotometer)

UV- Near : UV absorption (Spectrophotometer)

Visible : Absorption (Colorimeter and Spectrophotometer)

Infra-Red : IR and Raman: changes in the molecular and rotational and vibrational status

Microwave : Changes in rotational status of: Electron Spin (Microwave Spectroscopy and ESR)

Radio : Changes in rotational status of: Nuclear Spin (NMR)

Working Principle

Bragg’s LawBragg's law was used to explain the interference

pattern of X-rays scattered by crystals

Nλ = 2dhkl sinθq q d

hkl

dh

kl

Bragg diffraction• Two beams with identical wavelength and phase approach a crystalline

solid and are scattered off two different atoms within it. The lower beam traverses an extra length of 2dsinθ. Constructive interference occurs when this length is equal to an integer multiple of the wavelength of the radiation.

Experimental Setup

Source: http://pruffle.mit.edu/atomiccontrol/education/xray/xray_diff.php

How Does It WorkSo

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Crystal (regular array of atoms) is

mounted on a Goniometer

Bombarded with X-Ray while

rotating

Production of diffraction pattern

of regularly spaced spots

The 2-D images taken at different

rotation are converted to 3-D

models of the electron density map

by the method of Fourier

Transform

Some Example Images

UsesXRD is a non-destructive technique.

To determine structural properties such as Lattice

parameters (10-4Å), strain, grain size

Biological macromolecular crystallography

To determine atomic arrangement.

To measure thickness of thin films and multi-layers.

Raman spectroscopy

Raman spectroscopy (/ˈrɑːmən/; named after Sir C. V. Raman) is

a spectroscopic technique used to observe vibrational, rotational, and other low-

frequency modes in a system.[1] Raman spectroscopy is commonly used in

chemistry to provide a fingerprint by which molecules can be identified

It relies on inelastic scattering, or Raman scattering, of monochromatic light,

usually from a laser in the visible, near infrared, or near ultraviolet range. The

laser light interacts with molecular vibrations, phonons or other excitations in the

system, resulting in the energy of the laser photons being shifted up or down.

The shift in energy gives information about the vibrational modes in the

system. Infrared spectroscopy yields similar, but complementary, information.