YEDITEPE UNIVERSITY
BME 414 HOMEWORK
X-RAY DIFFRACTION
MELİSA YAPRAK
20100707022
Table of Contents
1. X-Ray Diffraction...................................................................................... 3
2. History ......................................................................................................... 3
3. Applications of XRD ................................................................................ 4
3.1.
3.2.
Pharmaceutical Industry ............................................................................. 4
Forensic Science .............................................................................................. 4
3.3. Geological Applications ................................................................................ 4
3.4. Microelectronics Industry ........................................................................... 4
3.5. Glass Industry ................................................................................................... 5
4. Bragg’s Law ................................................................................................ 5
5. Micro X-Ray Diffraction (µXRD) ........................................................ 6
6. Parallel Beam Geometry For Powder X-Ray Diffraction ............ 6
7. Parallel Beam X-ray Diffraction .......................................................... 7
8. Neutron Diffraction ................................................................................. 8
References ....................................................................................................... 9
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1. X-RAY DIFFRACTION
X-ray diffraction is a tool for the investigation of the structure of matter. X -rays are
scattered by interaction with the electrons of the atoms in the material being
investigated. The technique began when von Laue discovered that crystals
diffract x-rays in 1912. Since that day; it has been applied to chemical analysis,
stress and strain measurement, the study of phase equilibria, measurement of
particle size, as well as crystal structure.
2. HISTORY
X-ray diffraction has been a well-established technique in the field of structural
investigations for decades, applied not only by physicists. It represents an
important tool for chemists and biologists, too, and played a decisive role in the
discovery of the structure of the DNA in 1953. Any method that exploits x rays is
based upon their discovery in 1895 by W. C. Röntgen by chance while studying
the charge transport in gases. This achievement was rewarded the first Nobel
prize in the field of physics ever, in 1901. The first diffraction experiment was
performed by Max v. Laue in 1912. Fig 1 displays the observed diffraction pattern.
With this single photograph, Laue solved at once two major problems of his days:
It clearly reveals the crystalline nature of solids and proves that x rays behave like
waves. This finding was rewarded the Nobel prize in 1914. The first material is
the mineral aragonite and the second is calcite. X-ray diffraction can be used to
tell different crystal structures apart.
Fig 1
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3. Applications of XRD
Pharmaceutical industry:
X-ray diffraction (XRD) can be used to
unambiguously characterize the composition of pharmaceuticals. An XRD-pattern
is a direct result of the crystal structures, which are present in the pharmaceutical
under study. The parameters typically associated with crystal structure can be
simply accessed. For example, once an active drug has been isolated, an
indexed X-ray powder diffraction pattern is required to analyse the crystal
structure, secure a patent and protect the company’s investment. For multicomponent formulations, the actual percentages of the active ingredients in the
final dosage form can be accurately analysed in situ, along with the percentage of
anyamorphous packing ingredients used. XRD is the key technique for solid-state
drug analysis, benefiting all stages of drug development, testing and production.
Forensic science:
XRD is used mainly in contact trace analysis.
Examples of contact traces are paint flakes, hair, glass fragments, stains of any
description and loose powdered materials. Identification and comparison of trace
quantities of material can help in the conviction or exoneration of a person
suspected of involvement in a crime.
Geological applications:
XRD is the key tool in mineral exploration.
Mineralogists have been amongst the foremost to develop and promote the new
field of X-ray crystallography after its discovery. Thus, the advent of XRD has
literally revolutionized the geological sciences to such a degree that they have
become unthinkable without this tool. Nowadays, any geological group actively
involved in mineralogical studies would be lost without XRD to unambiguously
characterise the individual crystal structures. Each mineral type is defined by a
characteristic crystal structure, which will give a unique x-ray diffraction pattern,
allowing rapid identification of minerals present within a rock or soil sample. The
XRD data can be analysed to determine the proportion of the different minerals
present.
Microelectronics industry:
As the microelectronics industry uses
silicon and gallium arsenide single crystal substrates in integrated circuit
production, there is a need to fully characterise these materials using the XRD.
XRD topography can easily detect and image the presence of defects within a
crystal, making it a powerful non-destructive evaluation tool for characterising
industrially important single crystal specimens.
Glass industry:
While glasses are X-ray amorphous and do not
themselves give X-ray diffraction patterns, there are still manifold uses of XRD in
the glass industry. They include identification of crystalline particles which cause
tiny faults in bulk glass, and measurements of crystalline coatings for
texture, crystallite size and crystallinity.
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4. Bragg’s Law
English physicists Sir W.H. Bragg and his son Sir W.L. Bragg developed a
relationship in 1913 to explain why the cleavage faces of crystals appear to reflect
X-ray beams at certain angles of incidence (theta, q). The variable d is the
distance between atomic layers in a crystal, and the variable lambda l is the
wavelength of the incident X-ray beam; n is an integer. This observation is an
example of X-ray wave interference(Roentgenstrahlinterferenzen), commonly
known as X-ray diffraction (XRD), and was direct evidence for the periodic atomic
structure of crystals postulated for several centuries.
Where n is an integer, λ is the wavelength of incident wave, d is the spacing
between the planes in the atomic lattice, and θ is the angle between the incident
ray and the scattering planes.
The Incident Beam
The beam that comes
strikes to the surface.
and
INCIDENT BEAM is used to be
made of TUNGSTEN but now
COPPER is used because it is
easy to cool down.
The Diffracted Beam
When the electron beam passes
through the thin crystalline
sample, it is diffracted by the
atomic planes in the sample
when the Bragg condition is
satisfied.
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5. Micro X-ray Diffraction (µXRD)
Micro X-ray diffraction (µXRD) is a structural analysis technique which allows for
the examination of very small sample areas. Like conventional XRD
instrumentation, µXRD relies on the dual wave/particle nature of X-rays to obtain
information about the structure of crystalline materials. Unlike conventional XRF,
which has a typical spatial resolution ranging in diameter from several hundred
micrometers up to several millimeters, µXRD uses X-ray optics to focus the
excitation beam to a small spot on the sample surface so that small features on
the sample can be analyzed.
Polycapillary focusing optics collect X-rays from the divergent X-ray source and
direct them to a small focused beam at the sample surface with diameters as
small as tens of micrometers. The resulting increased intensity delivered to the
sample in a small focal spot allows for enhanced spatial resolution for small
feature analysis and enhanced performance for diffraction measurement of small
specimens. Unlike conventional XRD instrumentation which is bulky and has high
power requirements, microdiffraction with high diffracted-beam intensity can be
achieved with a very low-power source using these optics.
6. Parallel Beam Geometry for Powder X-ray
Diffraction
Some of the major drawbacks of traditional parafocusing XRD for diffraction
measurement of powder samples are that it requires very precise source-sampledetector alignment and carefully prepared samples. Errors often result from
differences in sample position, shape, roughness, flatness, and transparency.
Furthermore, small diffraction intensities may result due to the small parafocusing
source irradiation area as the number of crystals in a powder satisfying the Bragg
condition depends on the volume irradiated by the beam and the crystallite size.
Parallel beam XRD using polycapillary collimating optics can be used to enhance
powder XRD experiments. Due to the insensitivity of parallel beam XRD to
sample geometry and displacement errors, minimal sample preparation is
required for powder samples. An additional benefit of using a collimated beam for
X-ray powder diffraction is to spread the incident beam over a large region,
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allowing many more crystals to be in diffracting condition compared to the area
typically irradiated with a parafocusing instrument.
7. Parallel Beam X-ray Diffraction
Some of the major drawbacks of traditional XRD are that it is often based on
bulky equipment with high power requirements. Furthermore, most conventional
instruments use a parafocusing Bragg-Brentano geometry, offering the
advantages of high-resolution and high beam-intensity analysis at the cost of very
precise alignment requirements and carefully prepared samples. Additionally, this
geometry requires that the source-to-sample distance be constant and equal to
the sample-to-detector distance. Ensuing errors often lead to difficulties in phase
identification and improper quantification. A mis-positioned sample, a partially
transparent sample, or a rough sample can lead to unacceptable specimen
displacement errors. The sample flatness, roughness, and positioning constraints
usually preclude in-line measurements. These constraints are removed if the
incident X-ray beam is parallel.
In parallel beam XRD, a polycapillary collimating optic can be used to form an
intense parallel X-ray excitation beam resulting in very high X-ray intensities at
the sample surface.
With parallel-beam geometry, the sample position can vary and the XRD system
is no longer constrained to maintain the same distance between the X-ray source
and sample as between the sample and detector. The geometric flexibility can
accommodate existing manufacturing conditions and can be used on a much
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broader range of sample shapes and sizes. Parallel beam XRD is not only
insensitive to errors associated with sample displacement; it virtually eliminates
all of the other well-known instrument error functions, which contribute to
asymmetric peak broadening, such as non-flat or rough specimens, axial
divergence, and sample transparency. As a result, minimal sample preparation is
required. Furthermore, through use of a polycapillary collimating optic, the target
parallel beam XRD system can be combined with a low power X-ray source,
reducing instrument size and power requirements. Parallel beam XRD using Xray optics has been successfully used for applications including thin film analysis,
sample texture evaluation, monitoring of crystalline phase and structure, and
investigation of sample stress and strain.
The elimination of multiple sources of error and the potential for reducing the
power, size, weight, and cost of an instrument makes parallel beam X-ray
systems natural candidates for on-line diffraction systems for quality control and
feedback in manufacturing and process environments. Parallel-beam XRD has
been successfully used in process applications for phase distribution
measurements in the pharmaceutical and steel industries, thin film texture
measurements for superconductor layers and magnetic films, and structure
measurements for proteins.
8. Neutron Diffraction
Single crystal and powder neutron diffraction can be enhanced through the use of
polycapillary focusing optics for convergent beam neutron crystallography. Using
polycapillary optics, neutrons can be focused into a small spot resulting in an
increased neutron current density on the sample. Polycapillary optics can also
provide large gains over conventional unfocused neutron beams. Convergent
beam neutron crystallography using capillary optics can be effectively used in
crystal structure or phase distribution studies for small samples of small-tomedium-size molecules. This is particularly important for ultra high pressure or
low temperature measurements. Enhanced thin film analysis Powder diffraction
using neutron focusing optics enables the analysis of small samples or weakly
diffracting polycrystalline materials such as polymers. High spatial resolution
studies of strain, phase, and texture distributions in extended samples may also
be possible.
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9. REFERENCES
1. http://www.ammrf.org.au/myscope/xrd/additional/
2. http://www.diss.fuberlin.de/diss/servlets/MCRFileNodeServlet/FUDISS_derivate_000000002
709/06_ch3.pdf?hosts=
3. http://chemwiki.ucdavis.edu/Analytical_Chemistry/Instrumental_Analysis/Di
ffraction/Bragg%27s_Law
4. http://www.xos.com/techniques/xrd/
5. http://materialsection.files.wordpress.com/2011/09/1-1-xray_diffractionbragg-law.pdf
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