About the type of Electron microscope

1. ELECTRON MICROSCOPE
By:
K.Sanjay
BP211525
I MSc Applied Microbiology
To:
Dr.K.Amala.,MSc.,Mphil.,Phd
Department of Microbiology

2. ELECTRON MICROSCOPE
 Objects smaller than about 0.2 µm, such as viruses or the internal structures of
cells, must be examined with an electron microscope.
 In Electron microscopy, a beam of electrons is used instead of light. Like light,
free electrons travel in waves.
 The resolving power of the electron microscope is far greater than that of the
other microscopes.
 Images produced by electron microscopes are always black and white, but they
may be colored artificially to accentuate certain details.
 Instead of using glass lenses, an electron microscope uses electromagnetic
lenses to focus a beam of electrons onto a specimen. There are two types of
Electron microscopes: the Scanning electron microscope (SEM) and Transmission
electron microscope (TEM).

3. SCANNING ELECTRON MICROSCOPE
Working Principle
 In Scanning Electron Microscopy (SEM), an Electron gun produces a finely
focused beam of electrons called the Primary electron beam.
 The Primary electron beam passes through the Electromagnetic condenser
lenses and is directed over the surface of the Specimen. The specimen is
usually placed on Aluminium stubs.
 The Primary electron beam knocks electrons out of the surface of the
Specimen, and the Secondary electrons thus produced are transmitted to an
Electron collector, Amplified and used to produce an image on a Viewing
screen or Photographic plate. The image is called as Scanning Electron
Micrograph.

4. Uses
 SEM is especially useful in studying the surface morphology of the specimens,
macromolecular aggregates and tissues (usually magnified 1000 – 1,00,000 X).
 SEM has a variety of applications in a number of scientific research and
industry - related fields, especially where characterizations of solid materials
is beneficial.

5. TRANSMISSION ELECTRON MICROSCOPE
 Working Principle
 In Transmission Electron Microscope (TEM), a finely focused beam of electrons from an
Electron gun passes to a specially prepared, ultrathin section of the specimen through
Electromagnetic condenser.
 Electron microscopes use electromagnetic condenser lenses to control illumination, focus,
and magnification. The specimen is usually placed on a Copper mesh grid.
 The beam of electrons passes through the Specimen and then through an Electromagnetic
objective lens, which magnifies the image.
 Finally, the electrons are focused by an Electromagnetic projector lens onto a Fluorescent
screen or Photographic plate. The final image is called a Transmission electron
micrograph.

6. Uses
 TEM is used to show the multiple characteristics of objects such as
Ultrastructure of cell, Crystallization, Viruses and Tissues (usually magnified
10,000 – 1,00,000 X).
 TEM is ideal for a number of different fields such as Life sciences,
Nanotechnology, Medical, Biological & Material research, Forensic analysis and
Metallurgy as well as industry and education.
 TEM provide topographical, morphological, compositional and crystalline
information.

7. Difference between SEM and TEM
Scanning Electron Microscope Transmission Electron Microscope
Low Resolution. Resolving power is 10
nm
High Resolution. Resolving power is 0.1
nm
Electron beam scans over the surface
of the sample
Electron beam pass through the sample
Magnifying power is 1,00,000 X Magnifying power is 50,00,000 X
Specimen preparation is easy Specimen preparation needs
skilled persons and very thin specimen
(100 nm) is required.

8. Scanning Electron Microscope Transmission Electron Microscope
Aluminium stubs are used for specimen
mounting
Thin films on Copper grid are used for
specimen mounting
Cheap Expensive
Relatively safe to human use Relatively detrimental to human health