The document summarizes electron microscopes. It describes that Ernst Ruska invented the first electron microscope in 1931, which uses a beam of electrons instead of light to magnify objects. It has three main parts - an electron gun that generates electrons, electromagnetic lenses that focus the electron beam, and a specimen holder. Electron microscopes can magnify objects up to two million times, allowing visualization of structures at the nanoscale. There are two main types - transmission electron microscopes (TEM), which produce highly detailed images but require thin specimens, and scanning electron microscopes (SEM) which scan surfaces and provide 3D topographic information.

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