The document discusses electron microscopy. It describes how electron microscopes use electron beams instead of light to image specimens. There are two main types: transmission electron microscopes, which image thin sections, and scanning electron microscopes, which image surfaces. Electron microscopes provide much higher magnification than light microscopes due to the small wavelength of electrons. They have many applications but also limitations such as not being able to image living specimens.

1. Electron Microscopy
Presentation of Biological Techniques.

2. Group 2
Anbar Kaneez Raza (15181514-038)
Najam ul Sehar Aiman (15181514-040)
Safia Irfan (15181514-018)
BS Zoology (VI)

3. Content of Presentation
 Introduction
 History
 Principle
 Types
 Advantages and disadvantages
 Limitation
 Summary

4. Introduction
 In electron microscope a beam of electron
is used instead of light. It is use for those
objects which are smaller than 0.2 micron
meter.
 It has greater resolution power then light
microscope because electron have 100,000
times shorter wavelength then light.
 It gives deep structures of specimens.
 Produces black and white images.
 Use electromagnetic lenses instead of glass
lenses.

5. Why we use electron microscope instead of light
microscope?
 The human eye can distinguish two points 0.2 mm apart, without the aid of any
additional lenses. ( resolving power of human eye)
 A modern light microscope has a maximum magnification of about 1000x.
 White light has wavelengths from 400 to 700 nanometers (nm).
 Then electron microscope can magnifies up to 100,000 times more then light
microscope.

6. Optical microscope image
of nanofibers
Scanning electron
microscope image at
4000x magnification of
same nanofibers

7. History of electron microscope
 The first electron microscope prototype was built in 1931 by
German engineers Ernst Ruska and Max Knoll
 Only capable of magnifying objects by four hundred times
 In 1937, Siemens developed the electron microscope further.
 Siemens produced the first commercial TEM in 1939, but the
first practical electron microscope had been built at the
University of Toronto in 1938, by Eli Franklin Burton and
students Cecil Hall, James Hillier, and Albert Prebus.
 Modern electron microscopes can magnify objects up to two
million times and based upon Ruska prototype.

8. Basic principle
 Work on basic principle on which light microscope works.
 Electrons are used for magnification and image formation,
 Image formation occurs by electron scatting and due to different lateral
absorption of the beam
I. Heavy atoms darkest
II. Light atoms high transmissions.
 The electron image converted into visible form by projecting on a fluorescent
screen.

9. Types of electron microscope
 There are two types of electron microscope:
1. Transmission Electron Microscope (TEM)
2. Scanning Electron Microscope (SEM)

10. Transmission Electron Microscope
(TEM)
 The transmission electron microscope
(TEM)
was the first electron microscope to be
developed. It works by shooting a beam of
electrons at a thin slice of a sample and
detecting those electrons that make it
through to the other side. The TEM lets us
look in very high resolution at a thin section
of a sample (and is therefore analogous to
the compound light microscope). This makes
it particularly good for learning about how
components inside a cell, such as organelles,
are structured.

11. 1. A high-voltage electricity supply powers the cathode.
2. The cathode is a heated filament, a bit like the electron gun
in an old-fashioned cathode-ray tube (CRT) TV. It generates a
beam of electrons that works in an analogous way to the
beam of light in an optical microscope.
3. An electromagnetic coil (the first lens) concentrates the
electrons into a more powerful beam.
4. Another electromagnetic coil (the second lens) focuses the
beam onto a certain part of the specimen.
5. The specimen sits on a copper grid in the middle of the main
microscope tube. The beam passes through the specimen
and "picks up" an image of it.
6. The projector lens (the third lens) magnifies the image.
7. The image becomes visible when the electron beam hits a
fluorescent screen at the base of the machine. This is
analogous to the phosphor screen at the front of an old-
fashioned TV .
8. The image can be viewed directly (through a viewing portal),
through binoculars at the side, or on a TV monitor attached
to an image intensifier (which makes weak images easier to
see).
Working

12. Scanning Electron Microscope
(SEM)
 Unlike the TEM, where
electrons of the high voltage
beam form the image of the
specimen, the Scanning
Electron Microscope (SEM)
produces images by
detecting low energy
secondary electrons which
are emitted from the surface
of the specimen due to
excitation by the primary
electron beam.

13. 1. Electrons are fired into the machine.
2. The main part of the machine (where the object is
scanned) is contained within a sealed vacuum chamber
because precise electron beams can't travel effectively
through air.
3. A positively charged electrode (anode) attracts the
electrons and accelerates them into an energetic beam.
4. An electromagnetic coil brings the electron beam to a
very precise focus, much like a lens.
5. Another coil, lower down, steers the electron beam from
side to side.
6. The beam systematically scans across the object being
viewed.
7. Electrons from the beam hit the surface of the object and
bounce off it.
8. A detector registers these scattered electrons and turns
them into a picture.
9. A hugely magnified image of the object is displayed on a
TV screen.
Working

14. Differences between TEM and SEM
Transmission electron microscope
 It is used to observe finer details of
internal structures.
 Uses electromagnetic coils and high
voltages.
 Electrons beams are passing
through the specimen
 Flat images produced by TEMs
Scanning electron microscope
 This microscope is used to observe the
surface structure of microscopic
objects.
 Uses low voltages
 Instead of traveling through the
specimen, the electron beam
effectively bounces straight off it.
 Are generally about 10 times less
powerful than TEMs
 Produce very sharp, 3D images

16. Electron Microscope Advantages
 The primary advantage is its powerful magnification.
 The potential runs the gamut of scientific fields including biology,
gemology, medical and forensic sciences, metallurgy and
nanotechnologies.
 EMs also have many technological and industrial applications, such as
semiconductor inspection, computer chip manufacturing, quality control
and can even be used as part of a production line.

17. Electron Microscope Disadvantages
 High cost, size, maintenance, researcher training and image artifacts resulting from
specimen preparation.
 It is a large, cumbersome, expensive piece of equipment, extremely sensitive to vibration
and external magnetic fields.
 It needs to be kept in an area large enough to contain the microscope as well as protect
and avoid any unintended influence on the electrons.
 Upkeep involves maintaining stable voltage supplies, currents to electromagnetic
coils/lens and circulation of cool water so the samples are not damaged or destroyed
from heat given off during the process of energizing the electrons.
 Special training is required to learn the involved processes of specimen preparation, to
minimize and recognize preparation-related artifacts and to operate the microscope
itself.

18. Limitations of electron
 The limitations of electron microscopes are as follows:
(a) Live specimen cannot be observed.
(b) As the penetration power of 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.

19. Summary
 Electrons microscopes are used widely to see small structures.
 Its based upon electron beam instead of light rays.
 Electrons have smaller wavelength then light rays.
 There are two types of EM (transmission and scanning electron microscope).
 EM widely used in industries, laboratories etc.
 EM have limitations that living objects can not be observed in it.