An electron microscope uses accelerated electron beams to provide high-resolution images, capable of magnifying objects at the nanometer scale. There are two main types: transmission electron microscope (TEM), which produces detailed internal images, and scanning electron microscope (SEM), which scans surfaces to reveal morphology and composition. While electron microscopy has advantages such as superior magnification and diverse applications, it also has limitations like inability to analyze live specimens and high costs.

1. Electron
Microscopy
prepared by:
Emad Adnan

2. WHAT IS AN ELECTRON MICROSCOPE?
 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 nanometers, which are formed by controlled
use of electrons in a vacuum captured on a phosphorescent
screen.
•Types of electron microscopes:
Transmission Electron Microscope (TEM)
Scanning Electron Microscope (SEM)

3. WORKING PRINCIPLE OF ELECTRON MICROSCOPE
 Electron microscopes use signals arising from the interaction of an
electron beam with the sample to obtain information about structure,
morphology, and composition.
An electron gun generates electrons that are focused into a narrow beam by
condenser lenses. The beam is accelerated using a high voltage (100 kV to
1000 kV) applied between a tungsten filament and an anode. The specimen,
which is very thin (20-100 nm), is placed on a holder. As the electron beam
passes through, electrons scatter based on the specimen's thickness and
refractive index; denser areas scatter more electrons and appear darker,
while less dense areas appear brighter. The objective lens then creates a
magnified intermediate image, which is further magnified by ocular lenses to
produce the final image.

5. PARTS OF ELECTRON MICROSCOPE
 Electron Microscope is in the form of a tall vacuum column that is vertically mounted. It has the following components:
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.
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.

6. PARTS OF ELECTRON MICROSCOPE

7. TRANSMISSION ELECTRON MICROSCOPE
(TEM)
 This is a 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 working principle of the Transmission Electron Microscope
(TEM) is similar to the light microscope. The major difference is
that 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.

9. LIMITATIONS OF TRANSMISSION ELECTRON
MICROSCOPE (TEM)
1.Generally, the TEMs are very expensive to purchase
2.They are very big to handle.
3.The preparation of specimens to be viewed under the
TEM is very tedious.
4.The use of chemical fixations, dehydrators, and
embedment's can cause the dangers of artifacts.
5.They are laborious to maintain.
6.It requires a constant inflow of voltage to operate.

10. SCANNING ELECTRON MICROSCOPE (SEM)
is a type of electron microscope that scans surfaces of
microorganisms that uses a beam of electrons moving
at low energy to focus and scan specimens. The
development of electron microscopes was due to the
inefficiency of the wavelength of light microscopes.
electron microscopes have very short wavelengths in
comparison to the light microscope which enables
better resolution power.

12. PRINCIPLE OF SCANNING ELECTRON MICROSCOPE (SEM)
 Unlike the Transmission Electron Microscope which uses transmitted electrons,
the scanning electron Microscope uses emitted electrons. The Scanning 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.

13. Principle of Scanning Electron Microscope

14. ADVANTAGES OF ELECTRON MICROSCOPY
 Electron microscopy has several main advantages. These include:
• Magnification and higher resolution – as electrons rather than light waves are used, it can be
used to analyze structures which cannot otherwise be seen. The resolution of electron
microscopy images is in the range of up to 0.2 nm, which is 1000x more detailed than light
microscopy.
• Diverse applications – Electron microscopy has a diverse range of applications in many
different fields of research including technology, industry, biomedical science and chemistry.
Examples of applications include semiconductor inspection, computer chip manufacture,
quality control and assurance, analysis of atomic structures, and drug development.
• High-quality images – With proper training, an electron microscope operator can use the
system to produce highly detailed images of structures which are of a high quality, revealing
complex and delicate structures that other techniques may struggle to reproduce

15. DISADVANTAGES OF ELECTRON MICROSCOPY
• Inability to analyze live specimens – As electrons are
easily scattered by other molecules in the air, samples
must be analyzed in a vacuum. This means that live
specimens cannot be studied by this technique. This
means that biological interactions cannot be properly
observed, which limits the applications of electron
microscopy in biological research.
• Black and white images – Only black and white
images can be produced by an electron microscope.
Images must be falsely colorized.

16. • Artefacts – These may be present in the image produced.
Artefacts are left over from sample preparation and require
specialized knowledge of sample preparation techniques to
avoid.
• Cost – Electron microscopes are expensive pieces of highly
specialized equipment. As most projects have limited budgets, it
may prove detrimental to use an electron microscope in the
research. However, running costs can be similar to alternatives
such as confocal light microscopes, so the investment in a basic
electron microscope is still worth considering even if budgetary
concerns are a major factor in decisions against utilizing the
technology.
DISADVANTAGES OF ELECTRON
MICROSCOPY

17. • Size – Despite the advantages in technology over the years,
electron microscopes are still large, bulky pieces of
equipment which require plenty of space in a laboratory. Also,
as electron microscopes are highly sensitive, magnetic fields
and vibrations caused by other lab equipment may interfere
with their operation. Consideration must be given to this if
the researcher is looking to install an electron microscope in
their laboratory.
• Training – Specialist operators are required to operate
electron microscopes, and these can undergo years of
training to properly use this technology.
DISADVANTAGES OF ELECTRON
MICROSCOPY

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