Electron microscopy by SIVASANGARI SHANMUGAM. Electron microscopy is a technique for obtaining high-resolution images of biological and non-biological specimens.

1. SIVASANGARI SHANMUGAM
ELECTRONMICROSCOPY

2. CONTENTS
1. Introduction
2. Types
3. Principles
4. Parts of Microscope
5. How does it works?
6. Applications
7. Advantages
8. Disadvantages

3. INTRODUCTION
 Electron microscopy is a technique for obtaining high resolution images of
biological and non-biological specimens.
 It is used in biomedical research to investigate the detailed structure of tissues,
cells, organelles and macromolecular complexes.
 The high resolution of EM images results from the use of electrons (which
have very short wavelengths) as the source of illuminating radiation.
 Electron microscopy is used in conjunction with a variety of ancillary
techniques (e.g. thin sectioning, immuno-labeling, negative staining) to answer
specific questions.

4.  EM images provide key information on the structural basis of cell function and
of cell disease.
 Ernst Ruska (1906-1988), a German engineer and academic professor, built the
first Electron Microscope in 1931, and the same principles behind his
prototype still govern modern EMs.
 An electron microscope is a microscope that uses a beam of
accelerated electrons as a source of illumination.
 It is a special type of microscope having a high resolution of images, able to
magnify objects in nanometres, which are formed by controlled use of
electrons in vacuum captured on a phosphorescent screen.

5. TYPES
There are two main types of electron microscope.
1. Transmission Electron Microscope (TEM)
2. Scanning Electron Microscope (SEM)
 TEM- It is used to view thin specimens (tissue sections, molecules, etc)
through which electrons can pass generating a projection image.
 SEM- It depends on the emission of secondary electrons from the
surface of a specimen.

6. PRINCIPLES
 Electron microscope works on the principle of
applying kinetic energy to produce signals on the
interaction of the electrons.
 These electrons are secondary electrons,
backscattered electrons and diffracted
backscattered electrons which are used to view
crystallized elements and photons.
 Secondary and backscattered electrons are used to
produce an image.
 The secondary electrons are emitted from the
specimen play the primary role of detecting the
morphology and topography of the specimen
while the backscattered electrons show contrast in
the composition of the elements of the specimen.

7.  Electron gun- The electron gun is a heated tungsten filament, which
generates electrons.
 Condenser lens - Focuses the electron beam on the specimen. A second
condenser lens forms the electrons into a thin tight beam.
 Specimen Holder- The specimen holder is an extremely thin film of carbon
held by a metal grid.
 Image viewing and Recording System-The final image is projected on a
fluorescent screen. Below the fluorescent screen is a camera for recording
the image.

8. PARTS OF ELECTRON MICROSCOPE
1. Electron gun
2. Electromagnetic lens
3. Condenser lens
4. Specimen holder
5. Recording system

9.  Objective lens- The electron beam coming out of the specimen passes down
the second of magnetic coils called the objective lens, which has high power
and forms the intermediate magnified image.
 Ocular lens- The third set of magnetic lenses called projector (ocular)
lenses produce the final further magnified image.
 Each of these lenses acts as an image magnifier all the while maintaining an
incredible level of detail and resolution.

10. HOW DOES IT WORKS?
 The electron gun generates electrons.
 Two sets of condenser lenses focus the electron beam on the specimen and
then into a thin tight beam.
 To move electrons down the column, an accelerating voltage (mostly between
100 kV-1000 kV) is applied between tungsten filament and anode.
 The specimen to be examined is made extremely thin, at least 200 times
thinner than those used in the optical microscope. Ultra-thin sections of 20-100
nm are cut which is already placed on the specimen holder.
 The electronic beam passes through the specimen and electrons are scattered
depending upon the thickness or refractive index of different parts of the
specimen.

11. HOW DOES IT WORKS?
 The denser regions in the
specimen scatter more electrons
and therefore appear darker in the
image since fewer electrons strike
that area of the screen. In contrast,
transparent regions are brighter.
 The electron beam coming out of
the specimen passes to the
objective lens, which has high
power and forms the intermediate
magnified image.
 The ocular lenses then produce the
final further magnified image.

12. APPLICATIONS
1. Electron microscopes are used to investigate the ultra structure of a wide
range of biological and inorganic specimens including microorganisms,
cells, large molecules, biopsy samples, metals, and crystals.
2. Industrially, electron microscopes are often used for quality control
and failure analysis.
3. Modern electron microscopes produce electron micrographs using
specialized digital cameras and frame grabbers to capture the images.
4. Science of microbiology use EM to study of microorganisms like bacteria,
virus and other pathogens have made the treatment of diseases very
effective.

13. ADVANTAGES
1. Very high magnification
2. Incredibly high resolution
3. Material rarely distorted by preparation
4. It is possible to investigate a greater depth of field
5. Diverse applications

14. DISADVANTAGES
1. The live specimen cannot be observed.
2. As the penetration power of the electron beam is very low, the object should be
ultra-thin. For this, the specimen is dried and cut into ultra-thin sections before
observation.
3. As the EM works in a vacuum, the specimen should be completely dry.
4. Expensive to build and maintain
5. Requiring researcher training
6. Image artifacts resulting from specimen preparation.
7. This type of microscope is a large, cumbersome extremely sensitive to vibration
and external magnetic fields.

15. REFERENCES
1. https://microbenotes.com/electron-microscope-principle-types-components-
applications-advantages-
limitations/#:~:text=An%20electron%20microscope%20is%20a,captured%2
0on%20a%20phosphorescent%20screen.
2. https://bitesizebio.com/29197/introduction-electron-microscopy-biologists/
3. https://www.umassmed.edu/cemf/whatisem/

16. THANK YOU