The document provides a comprehensive overview of electron microscopes, detailing their history, types, working principles, and applications. It explains the significant advancements in magnification and resolution achieved with electron microscopes compared to light microscopes. The applications range from biological research to forensic analysis, highlighting their importance in various scientific fields.

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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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11. Structural Parts of TEM
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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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21. Structural Parts of SEM
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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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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

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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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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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