Introduction History Resolution &Magnification of Electron microscope Types of electron microscope 1) Transmission electron microscope (TEM) - Structural parts of TEM - Principle & Working of TEM - Sample preparation for TEM - Advantages & disadvantages of TEM Scanning electron microscope (SEM) - Structural parts of SEM - Principle & Working of SEM - Sample preparation for SEM - Advantages & disadvantages of SEM 3) Scanning transmission electron microscope (STEM) Applications of electron microscope Conclusion References

1. 1
By
KAUSHAL KUMAR SAHU
Assistant Professor (Ad Hoc)
Department of Biotechnology
Govt. Digvijay Autonomous P. G. College
Raj-Nandgaon ( C. G. )

2. CONTENTS
• Introduction
• History
• Resolution &Magnification of
• Electron microscope
• Types of electron microscope
1) Transmission electron microscope (TEM)
- Structural parts of TEM
- Principle & Working of TEM
- Sample preparation for TEM
- Advantages & disadvantages of TEM
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3. 2) Scanning electron microscope (SEM)
- Structural parts of SEM
- Principle & Working of SEM
- Sample preparation for SEM
- Advantages & disadvantages of SEM
3) Scanning transmission electron microscope
(STEM)
• Applications of electron microscope
• Conclusion
• References
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4. INTRODUCTION
• Electron microscope work by using an
electron beam instead of visible light & an
electron detector instead of our eyes & the
magnification is obtained by electromagnetic
field .
• Electron beam has the properties of a wave
with a wavelength that is much smaller than
visible light .
• The smaller is the wavelength of light , the
greater is the resolving power .
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5. • Electron microscope examine objects on a
very fine scale & this examination can yield
information about the topography ,
morphology , composition & crystallographic
information .
• The electron microscope is best used for
studying biological ultra-structure & the image
obtained is called electron micrograph .
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6. HISTORY
• The first electromagnetic lens was developed in 1931
by Hans Busch .
• It was Ernst Ruska & Max Knoll , a physicist & an
electrical engineer , respectively from the University
of Berlin , who created the first electron microscope
in 1931 .
• The first commercial electron microscope was
produced in 1938 by Siemens .
• Albert Prebus & Siemens produced a transmission
electron microscope (TEM) in 1939 .
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7. RESOLUTION & MAGNIFICATION
• Resolution power is the ability of an imaging device
to see objects distinctly , that are located at a small
angular distances .
• Magnification in terms is defined as “a measure of
the ability of a lens or other optical instruments to
magnify , expressed as the ratio of the size of the
image to that of the object” .
• This means , that an object of any size is magnified
to form an enlarged image .
• Thus , the resolving power of an electron microscope
is 200 times greater than that of a light microscope .
• It produces useful magnification up to X 400,000 as
compared to X 2000 in a light microscope .
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8. TYPES OF ELECTRON MICROSCOPE
• There are three types of electron microscope
as described below :-
1) Transmission electron microscope (TEM)
2) Scanning electron microscope (SEM)
3) Scanning transmission electron microscope
(STEM)
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9. 1) TRANSMISSION ELECTRON
MICROSCOPE (TEM)
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10. 10

11. Structural Parts of TEM
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12. 12

13. Principle & Working of TEM
• Specimen is bombarded by a beam of electrons ,
the primary electrons . The bombarding
electrons are focused onto the object .
• In areas in the object where these electrons
encounter atoms with a heavy atomic nucleus ,
they rebound .
• In regions where the material consist of lighter
atoms , the electrons are able to pass through .
• The fine pattern of electrons leaving the object ,
reaches the objective lens forms the image .
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14. • It is then greatly enlarged by projector lens .
• Eventually , the tranversing electrons
(transmission) reach the scintillator plate at
the base of the column of the microscope .
• The scintillator contains phosphor compounds
that can absorb the energy of the stricking
electrons & convert it to light flashes .
• Thus , a contrasted image is formed on this
plate .
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15. Sample Preparation for TEM
• The material to be studied under electron
microscope must be well preserved , fixed ,
completely dehydrated , ultrathin & impregnated
with heavy metals that sharpen the difference
among various organelles .
• The material is preserved by fixation with
glutaraldehyde & then with osmium tetroxide .
• The fixed material is dehydrated & then embedded
in plastic (epoxy resin) & sectioned with the help of
diamond or glass razor of ultra- microtome .
• The sections are ultrathin about 50-100 nm thick .
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16. • These sections are placed on a copper grid &
exposed to electron dense materials like lead
acetate , uranylacetate , palladium vapours ,
phosphotungstate etc . Now the sections can
be viewed in the TEM .
• The coating with electrons dense materials
enables the specimen to withstand electric
bombardment .
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17. Advantages of TEM
• TEMs offer very powerful magnification &
resolution .
• TEMs provide information on element &
compound structure .
• Images are high – quality & detailed .
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18. Disadvantages of TEM
• TEMs are large & expensive .
• Laborious sample preparation .
• Operation & analysis requires special training .
• Samples are limited to those that are electron
transparent .
• TEMs require special housing & maintainance .
• Images are black & white .
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19. 2) SCANNING ELECTRON
MICROSCOPE (SEM)
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20. 20

21. Structural Parts of SEM
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22. 22

23. Principle & Working of SEM
• The electron gun produces an electron beam when
tungsten wire is heated by current .
• This beam is accelerated by the anode .
• The beam travels through electromagnetic fields &
lenses , which focus the beam down toward the
sample .
• A mechanism of deflection coils enables to guide
the beam so that it scans the surface of the sample
in a rectangular frame .
• When the beam touches the surface of the sample ,
it produces :
- Secondary electrons (SE)
- Back scattered electrons (BSE)
- X- Rays …
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24. • The emitted SE is collected by SED & convert it into
signal that is sent to a screen which produces the final
image .
• These signals are scanned in the manner of a television
system to produce an image on a cathode ray tube
(CRT) .
• The image is recorded by capturing it from the CRT .
• Additional detectors collects the X-rays , BSE & produce
corresponding images .
• A secondary electron detector (SED) attracts the SE &
depending on the number of electrons that reach the
detector , registers different levels of brightness on a
monitor .
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25. 25

26. 26

27. Sample Preparation for SEM
• The specimen is first fixed in liquid propane at-180
degree Celsius & then dehydrated in alcohol at-70
degree Celsius .
• The dried specimen is the coated with a thin film of
heavy metal , such as platinum or gold , by
evaporation in a vacuum provides a reflecting
surface of electrons .
• The surface of the specimen when scanned by the
electron beam release secondary electrons that
form a three-dimensional image of the specimen
on a television screen .
• Holes & fissures appear dark , & knobs & ridges
appear light .
• Complete scanning from top to bottom usually
takes only a few seconds 27

28. 28

29. Advantages of SEM
• It gives detailed 3D & topographical imaging &
the versatile information generated from
different detectors .
• Modern SEMs allow for the generation of data in
digital form .
• Most SEM samples require minimal preparation
actions .
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30. Disdavantages of SEM
• SEMs are expensive & large .
• Special training is required to operate an SEM .
• SEMs carry a small risk of radiation exposure
associated with the electrons that scatter from
beneath the sample surface .
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32. 32

33. 33

34. 3) SCANNING TRANSMISSION
ELECTRON MICROSCOPE (STEM)
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35. • A scanning transmission electron microscope
or STEM combines the capabilities of both a
SEM & a TEM.
• The electron beam is transmitted across the
sample to create an image (TEM) while it also
scans a small region on the sample (SEM) .
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36. APPLICATIONS OF ELECTRON
MICROSCOPE
• Electron microscope is being used today
in research laboratories around the world
to explore the molecular mechanisms of
disease , to visualize the 3D structure of
tissues & cells .
• Forensic science uses electron
microscopy to analyze criminal evidence
such as gunshot residue , clothing fibres ,
soil samples etc.
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37. • Inorganic particles – both natural & manmade
including soil , coal , cement , fly ash etc . can
be analyzed to provide more detailed
understanding of impact of waste pollution on
environment & health .
• In medical field electron microscope is used to
compare healthy & unhealthy blood & tissue
samples .
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38. CONCLUSION
• Since its invention , electron microscope
has been a valuable tool in the
development of scientific theory .
• Its wide spread is because it permit the
observation of material on a nanometer
(nm) to micrometer scale .
• Although SEMs & TEMs are large &
expensive , they remain popular among
researchers due to the high-resolution &
detailed images the produce
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39. References
• Electron microscope – Wikipedia
- https://en.m.wikipedia.org>wiki>Electr...
• Electron microscope : Principles & types
– Biology Discussion
- www.biologydiscussion
.com>microscope…
• Working principle of an electron
microscope
- www.yourarticlelibrary.com>working-p...
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