2. X RAY DIFFRACTION
• A technique used to determine 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.
• 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.
• A stream of x-rays directed at a crystal diffract and scatter as they
encounter atoms. the scattered rays interfere with each other and
produce spots of different intensities that can be recorded on film.
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4. the path difference between ray 1 and ray 2 = 2d sin
“constructive interference of the reflected beams emerging from two
different planes will take place if the path lengths of two rays is equal
to whole number of wavelengths”.
for constructive interference,
nλ=2dsin
this is called as bragg’s law
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8. APPLICATION OF XRD
• Structure of crystals
• Polymer characterization
• Particle size determination
• Applications of diffraction methods to complexes
I. Determination of cis-trans isomerism
II. Determination of linkage isomerism
• Miscellaneous applications
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9. SCANNING ELECTRON MICROSCOPE
• Electron microscopes (SEM) are scientific instruments that use
a beam of energetic electrons to examine objects on a very
fine scale.
• Electron microscopes (SEM) were developed due to the
limitations of light microscopes which are limited by the
physics of light.
• Electron microscopes (SEM) have a greater resolving power than
a light-powered optical microscope, because electrons have
wavelengths about 100,000 times shorter than visible light .
• Magnifications of up to about 10,000,000x.
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11. LIMITATIONS
• SEM cannot detect very light elements (H, He, and Li).
• Samples must be solid and they must fit into the microscope chamber.
maximum size in horizontal dimensions is usually on the order of 10
cm, vertical dimensions should not exceed 40 mm.
• Very high vacuum, vibration free, large space.
• An electrically conductive coating must be applied to electrically
insulating samples .
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14. APPLICATIONS
• Topography and morphology
• Chemistry
• Crystallography
• Orientation of grains
• In-situ experiments
I. Reactions with atmosphere
II. Effects of temperature
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17. ATOMIC FORCE MOCROSCOPY
• AFM works by scanning a probe over the sample surface,
building up a map of the height or topography of the surface as it
goes along
• No need of focusing, illumination, depth of field.
• It also have height information that make it simple to quickly
measure the height, volume, width of any feature in the sample.
• It physically feels the sample’s surface with a sharp probe,
building up a map of the height of samples surface.
• It provides single atomic level structure so provide high
resolution.
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20. LIMITATIONS
• AFM can only image a maximum height on the order of 10-20
micrometers and a maximum scanning area of about 150×150
micrometers.
• The scanning speed of an AFM is also a limitation.
• Highly dependent on AFM probes.
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21. COMPARISIONS
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SR. NO. XRD SEM AFM
SAMPLES CONDUCTIVE /
INSULATING /
SEMI CONDUCTER
MUST BE
CONDUCTIVE
CONDUCTIVE/
INSULATING
MAGNIFICATION 2 DIMENSIONAL 2 DIMENSIONAL 3 DIMENSIONAL
ENVIORNMENT VACUUM VACUUM VACUUM/ AIR/
LIQUID
TIME FOR IMAGE 3- 5 min 0.1 - 1 min 1-5 min
HORIZONTAL
REVOLUTION
5 nm 5 nm 2 nm
VERTICAL
REVOLUTION
- - 0.05 nm
FIELD OF VIEW 1 mm 1mm 0.01 mm
DEPTH OF FIELD GOOD GOOD POOR
CONTRAST ON
FLATE SURFACE
POOR POOR GOODNITC MED
