4. X-RAY CRYSTALLOGRAPHY
X-ray crystallography is a technique used for determining 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, a crystallographer
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.
5. Since many materials can form crystals—such as salts, metals, minerals, semiconductors,
as well as various inorganic, organic, and biological molecules—X-ray crystallography
has been fundamental in the development of many scientific fields.
The method also revealed the structure and function of many biological molecules,
including vitamins, drugs, proteins and nucleic acids such as DNA.
X-ray crystallography is still the chief method for characterizing the atomic structure of
new materials and in discerning materials that appear similar by other experiments.
7. X-RAY PHOTOELECTRON SPECTROSCOPY
(XPS)
X-ray photoelectron spectroscopy is a surface sensitive quantitative spectroscopic
technique that measures the elemental composition at the parts per thousand range,
empirical formula, chemical state and electronic state of the elements that exist within
a material.
XPS spectra are obtained by irradiating a material with a beam of X-rays while
simultaneously measuring the kinetic energy and number of electrons that escape from
the top 0 to 10 nm of the material being analyzed.
XPS requires high vacuum (P ~ 10−8 milli bar) or ultrahigh vacuum (UHV; P < 10−9
milli bar) conditions, although a current area of development is ambient pressure XPS,
in which samples are analyzed at pressures of a few tens of milli bar.
XPS is a surface chemical analysis technique that can be used to analyze the surface
chemistry of a material in its as received state, or after some treatment.
8. XPS is also known as ESCA (Electron Spectroscopy for Chemical Analysis), an
abbreviation introduced by Kai Siegbahn's research group to emphasize the
chemical information that the technique provides.
In principle XPS detects all elements. In practice, using typical laboratory scale X-
ray sources, XPS detects all elements with an atomic number (Z) of 3 (lithium) and
above. It cannot easily detect hydrogen (Z = 1) or helium (Z = 2).
Detection limits for most of the elements are in the parts per thousand ranges.
Detection limits of parts per million (ppm) are possible, but require special
conditions: concentration at top surface or very long collection time.
XPS is routinely used to analyze inorganic compounds, metal alloys,
semiconductors, polymers, elements, catalysts, glasses, ceramics, paints, papers,
inks, woods, plant parts, makeup, teeth, bones, medical implants, biomaterials,
viscous oils, glues, ion modified Materials and many others.
9.
10. 10
RADIOLOGY
Radiology is a specialty that uses medical imaging to diagnose and treat diseases seen within the
body.
A variety of imaging techniques such as X-ray radiography, ultrasound, computed tomography
(CT) and magnetic resonance imaging (MRI) are used to diagnose and/or treat diseases.
The following procedures are currently widely available:
Central Nervous System: Brain , Spine
Cardiovascular System: heart, blood vessels
Musculoskeletal System: bone, muscles, and joints
Digestive, Urinary, and Respiratory System: intestines,
kidneys, liver, stomach, lungs
Reproductive System and Mammography: male and female
reproductive organs and breasts
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X-RAY IMAGING
Other imaging techniques:
Ultrasound - images due to speed of amounts of sound energy
Magnetic resonance – based on magnetic properties
Elastography - shows strain levels in tissue produced in response to small
external applied compressions
Absorption of X-ray and gamma-ray by different material for image:
today, 2-dimensional solid state detectors are used in place of films for X-
ray and gamma-ray imaging as shown in this image.
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MAMMOGRAPHY AND CT SCAN
X-rays provide the sharpest images of the breast's inner structure. Mammogram
detects small tumours and changes in the breast tissues.
Computed tomography (CT), scanner takes images by rotating an x-ray tube
around the body while measuring the constantly changing absorption of the x-ray
beam by different tissues in your body.
The sensitive scanner provides small differences
in absorption of the beam by various tissues.
The information is fed into a computer which
reconstruct images of thin cross sections of the
body.
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DEXA – DUEL ENERGY X-RAY
ABSORPTIOMETRY
Dual energy X-ray absorptiometry (DEXA) is
also called dual x-ray absorptiometry (DXA).
A high and a low energy x-ray beams pass
through the bone and the difference in absorption
is used to estimate the bone mineral density.
Bone mineral density (BMD) is an indication of bone mass.
BMD generally correlates with bone strength and its ability to bear weight.
Low BMS is osteoporosis with risk of easy bone fracture.
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IMPACT OF X-RAY DIFFRACTION
Using X-ray diffraction, nearly all structure of compounds
artificially made or isolated from nature have been determined,
including structures of semiconductors, DNA molecules, and
proteins.
Structure data banks serve science, technologies, and medicine
This is one of the diffraction X-ray tubes with beryllium
windows by Varian, operating at 60 keV, 1500 - 2000 wats,
target W, Mo, Cr ($3000 each).
15. 15
X-RAY DIFFRACTION RESULTS
Two X-ray diffraction patterns are shown here :
Top: diffraction pattern from Al-wire recorded on a film revealing
preferred orientation and size of micro-crystals in the wire.
Bottom: X-ray diffraction pattern of a single crystal showing
positive image of X-ray beams.
Intensities of these beams allows us to determine molecular and
crystal structures.
Various data banks of structures are now available for research and
development.
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POSITRON EMISSION TOMOGRAPHY (PET)
Positron emission tomography is a nuclear medicine
functional imaging technique that is used to observe
metabolic processes in the body.
The system detects pairs of gamma rays emitted indirectly
by a positron-emitting radionuclide which is introduced
into the body on a biologically active molecule.
In modern PET-CT scanners, three dimensional imaging is
often accomplished with the aid of a CT X-ray scan
performed on the patient during the same session, in the
same machine.
The function of the organs provides better diagnosis than
CT.
17. X-Rays-Medical Applications
X-rays are used in medicine for medical analysis.
Dentists use them to find complications, cavities and impacted teeth.
Soft body tissue are transparent to the waves.
Bones and teeth block the rays and show up as white on the black background
18. Below are some x-rays showing objects which have been swallowed by people.
The examples show an open safety pin and a child's stomach with all the pieces of a
magnetic toy re-aligned after he's swallowed them one by one.
19. X-rays having wavelengths of 0.04nm to 0.5nm represent another radiation source
for high-resolution design reproduction.
X-ray lithography was first demonstrated to obtain high-resolution designs using
X-ray proximity printing by Spears and Smith.
X-ray lithography can be extended optical resolution of 15 nm.
ESSENTIAL ELEMENTS IN X-RAY LITHOGRAPHY
A mask consisting of a pattern made with an X-ray absorbing material on a thin X-
ray transparent membrane.
An X-ray source of sufficient brightness.
An X-ray sensitive resist material.
X-RAY LITHOGRAPHY
20. The X-rays are typically from synchrotron radiation source, allowing rapid exposure.
X-ray lithography is expensive, because of the expense of operating a synchrotron.
The actual operating expenses without considering the initial investment of tens-of-millions of
dollars. Therefore, the LIGA process was developed to reduce the dependency on a synchrotron.
LIGA is a German acronym for Lithographie, Galvanoformung, Abformung (Lithography,
Electroplating, and Molding) that describes a fabrication technology used to create high-aspect-
ratio microstructures.
X-RAY LITHOGRAPHY CONT.
21. Short wavelength from X-rays 0.4-4 nm
No diffraction effect
Simple to use
Uniform refraction pattern
High resolution for small feature size
ADVANTAGES OF X-RAY LITHOGRAPHY
DISADVANTAGES OF X-RAY LITHOGRAPHY
Distortion in absorber
Masks are expensive to produce
22. X-ray lithography is primarily used in nanolithography
15 nm optical resolution
Utilizes short wavelength of 1 nm
Requires no lenses
Allows for small feature size
APPLICATION OF X-RAY LITHOGRAPHY