The document provides an overview of electron microscopes, detailing their components, working principles, types, advantages, and limitations. It highlights the discoveries of Ernst Ruska and explains how transmission (TEM) and scanning electron microscopes (SEM) operate and their applications in various fields. High resolution and magnification are emphasized as key benefits, while challenges such as cost, specimen preparation, and environmental sensitivity are noted.

1. Electron microscope
Dr. Rasika Deshmukh

2. What is an Electron Microscope?
• microscope that uses a beam of accelerated
electrons as a source of illumination.
• high resolution of images,
• able to magnify objects in nanometres

3. Discovered by
• Ernst Ruska (1906-1988), a German engineer
and academic professor, built the first Electron
Microscope in 1931
• The same principles behind his prototype still
govern modern EMs.

5. Parts of Electron Microscope
Form of a tall vacuum column that is vertically mounted.
1. Electron gun
• The electron gun is a heated tungsten filament, which generates electrons.
2. Electromagnetic lenses
• The condenser lens focuses the electron beam on the specimen.
• A second condenser lens forms the electrons into a thin tight beam.
• 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.
• 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.

6. Parts of Electron Microscope
3. Specimen Holder
• The specimen holder is an extremely thin film
of carbon or collodion held by a metal grid.
4. 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

7. Working Principle of Electron microscope
• 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 the 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.

8. Working Principle of Electron microscope
• The electronic beam passes through the specimen and electrons
are scattered depending upon the thickness or refractive index of
different parts of the specimen.
• 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.

9. Applications of Electron microscope:
• Investigate the ultrastructure of a wide range of
biological and inorganic specimens
• Used for quality control and failure analysis.
• Modern electron microscopes produce
electron micrographs using specialized digital
cameras and frame grabbers to capture the images.
• Study of microorganisms like bacteria, virus, and
other pathogens have made the treatment of
diseases very effective.

10. Advantages of Electron microscope
• Very high magnification
• Incredibly high resolution
• Material rarely distorted by preparation
• It is possible to investigate a greater depth of
field
• Diverse applications

11. Limitations of Electron microscope
• The live specimen cannot be observed.
• The object should be ultra-thin
• The specimen is dried and cut into ultra-thin sections before
observation.
• As the EM works in a vacuum, the specimen should be
completely dry.
• Expensive to build and maintain
• Requiring researcher training
• Image artifacts resulting from specimen preparation.
• This type of microscope is large, cumbersome extremely
sensitive to vibration and external magnetic fields.

12. Types of electron microscope
• Transmission Electron Microscope (TEM)
• Scanning Electron Microscope (SEM)

13. Transmission Electron Microscope (TEM)
• powerful electron microscope that uses a
beam of electrons to focus on a specimen
producing a highly magnified and detailed
image of the specimen.
• The magnification power is over 2 million
times, producing the image of the specimen
which enables easy characterization of the
image in its morphological features,
compositions

14. Principle of Transmission Electron Microscope (TEM)
• similar to the light microscope.
• light microscopes use light rays to focus and
produce an image while the TEM uses a beam of
electrons to focus on the specimen, to produce
an image.
• Electrons have a shorter wavelength in
comparison to light which has a long
wavelength.
• Better resolution

16. Applications of Transmission Electron Microscope (TEM)
• To visualize and study cell structures of bacteria, viruses,
and fungi
• To view bacteria flagella and plasmids
• To view the shapes and sizes of microbial cell organelles
• To study and differentiate between plant and animal cells.
• Its also used in nanotechnology to study nanoparticles
such as ZnO nanoparticles
• It is used to detect and identify fractures, damaged
microparticles which further enable repair mechanisms of
the particles.

17. Advantages of Transmission Electron Microscope (TEM)
• It has a very powerful magnification of about 2 million times that
of the Light microscope.
• It can be used for a variety of applications ranging from basic
Biology to Nanotechnology, to education and industrial uses.
• It can be used to acquire vast information on compounds and
their structures.
• It produces very efficient, high-quality images with high clarity.
• It can produce permanent images.
• It is easy to train and use the Transmission Electron Microscope

18. Limitations of Transmission Electron Microscope (TEM)
• Generally, the TEMs are very expensive to purchase
• They are very big to handle.
• The preparation of specimens to be viewed under the TEM is very tedious.
• The use of chemical fixations, dehydrators, and embedments can cause
the dangers of artifacts.
• They are laborious to maintain.
• It requires a constant inflow of voltage to operate.
• They are extremely sensitive to vibrations and electro-magnetic
movements hence they are used in isolated areas, where they are not
exposed.
• It produces monochromatic images, unless they use a fluorescent screen
at the end of visualization.

19. Transmission Electron Microscope (TEM) Images

20. Scanning Electron Microscope (SEM)
• type of electron microscope that scans
surfaces of microorganisms that uses a beam
of electrons moving at low energy to focus
and scan specimens.

21. Principle of Scanning Electron Microscope (SEM)
• applying kinetic energy to produce signals on the interaction
of the electrons.
• These electrons are secondary backscattered 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.

24. Applications of the Scanning Electron Microscope (SEM)
• It is used in a variety of fields including Industrial uses,
nanoscience studies, Biomedical studies, Microbiology
• Used for spot chemical analysis in energy-Dispersive X-
ray Spectroscopy.
• Used in the analysis of cosmetic components which are
very tiny in size.
• Used to study the filament structures of microorganisms.
• Used to study the topography of elements used in
industries.

25. Advantages of the Scanning Electron Microscope (SEM)
• They are easy to operate and have user-friendly
interfaces.
• They are used in a variety of industrial
applications to analyze surfaces of solid objects.
• Some modern SEMs are able to generate digital
data that can be portable.
• It is easy to acquire data from the SEM, within a
short period of time of about 5 minutes.

26. Limitations
• They are very expensive to purchase
• They are bulky to carry
• They must be used in rooms that are free of
vibrations and free of electromagnetic elements
• They must be maintained with a consistent
voltage
• They should be maintained with access to
cooling systems

33. Thank you