Download Electron Microscope (EM)

Electron Microscope (EM)
 Lab-2 Sunday 13/12/2015
An electron microscope is a type of microscope that uses a beam of
electrons to illuminate the specimen and produce a magnified image.
Electron microscopes (EM) have a greater resolving power than a lightpowered optical microscope, because electrons have wavelengths about
100,000 times shorter than visible light (photons), and magnifications of
up to about 10,000,000x, whereas ordinary.
 The electron microscope uses electrostatic and
electromagnetic
"lenses" to control the electron beam and focus it to form an image.
 These lenses are analogous to, but different from the glass lenses
of an optical microscopes that form a magnified image by focusing
light on or through the specimen.
 Electron microscopes are used to observe a wide range of
biological and inorganic specimens including microorganisms,
cells, large molecules, biopsy samples, metals, and crystals.
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Electron microscope constructed by Ernst Ruska in 1933
Electron microscope (E.M)
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A 1973 Siemens electron microscope, Musée des Arts et Métiers, Paris
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Electron microscope (E.M)
Electron microscope (E.M)
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History of the (EM)
 The electron microscope was invented and patented by Hungarian
physicist Leo Szilárd who declined to construct it.
 Instead, German physicist Ernst Ruska and electrical engineer Max
Knoll constructed the prototype electron microscope in 1931,
capable of four-hundred-power magnification.
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Electron microscope constructed by Ernst Ruska in 1933.
Light Micrograph of Human Red Blood Cells
Types of the Electron Microscope (E.M)
1-Transmission Electron Microscope (TEM)
 The original form of electron microscope, the transmission
electron microscope (TEM) uses a high voltage electron beam to
create an image.
 The electrons are emitted by an electron gun, commonly fitted with
a tungsten filament cathode as the electron source.
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 The electron beam is accelerated by an anode typically at +100
keV with respect to the cathode, focused by electrostatic and
electromagnetic lenses, and transmitted through the specimen that
is in part transparent to electrons and in part scatters them out of
the beam
 Biological specimens typically require to be chemically fixed,
dehydrated and embedded in a polymer resin to stabilize them
sufficiently to allow ultrathin sectioning.
 Sections of biological specimens, organic polymers and similar
materials may require special `staining' with heavy atom labels in
order to achieve the required image contrast.
Transmission Electron Microscope (TEM)
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Transmission Electron Micrograph of Human Red Blood Cells
Transmission Electron Micrograph of Mitochondrion
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Transmission Electron Micrograph of a Cross Section OF Cilia
2-Scanning Electron Microscope (SEM)
 Unlike the (TEM), where electrons of the high voltage beam carry
the image of the specimen, the electron beam of the scanning
electron microscope (SEM) does not at any time carry a complete
image of the specimen.
 The (SEM) produces images by probing the specimen with a
focused electron beam that is scanned across a rectangular area of
the specimen (raster scanning).
 When the electron beam interacts with the specimen, it loses
energy by a variety of mechanisms.
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Scanning Electron Microscope (SEM)
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Main structures in the (SEM)
Scanning Electron Micrograph of Human Red Blood Cells
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Scanning Electron Micrograph of a Blood Clot
Scanning Electron Micrograph of the Mucous Membrane Lining the
Trachea
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Types of (SEM)
A-Environmental Scanning Electron Microscope (ESEM)
 Can produce images of sufficient quality and resolution with the
Samples being wet or contained in low vacuum or gas.
 This greatly facilitates imaging biological samples that are
unstable in the high vacuum of conventional electron microscopes.
B-Low Temperature Scanning Electron Microscope (LTSEM)
 Can use in the studying of the freezing specimen and crystals.
3-Reflection Electron Microscope (REM)
In the reflection electron microscope (REM) as in the (TEM), an
electron beam is incident on a surface, but instead of using the
transmission (TEM) or secondary electrons (SEM), the reflected
beam of elastically scattered electrons is detected.
4-Scanning Transmission Electron Microscope
(STEM)
 The (STEM) rasters a focused incident probe across a
specimen that (as with the TEM) has been thinned to
facilitate detection of electrons scattered through the
specimen.
 The high resolution of the (TEM) is thus possible in
(STEM).
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 The focusing action (and aberrations) occur before the
electrons hit the specimen in the (STEM), but afterward in
the (TEM).
 The (STEM) use of SEM-like beam rastering
simplifies annular dark-field imaging, and other
analytical techniques, but also means that image data
is acquired in serial rather than in parallel fashion.
 Often (TEM) can be equipped with the scanning
option and then it can function both as (TEM and
STEM).
5-Low-Voltage
Electron
Microscope
(LVEM)
 The Low-Voltage Electron Microscope (LVEM) is a combination
of (SEM, TEM and STEM) in one instrument, which operates at
relatively low electron accelerating voltage of 5 kV.
 Low voltage reduces the specimen damage by the incident
electrons and increases image contrast that is especially important
for biological specimens.
 Resolutions of a few nm are possible in (TEM, SEM and STEM)
modes.
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Applications of the (EM)
1-Protein localization
2-Electron tomography
3-Cellular tomography
4-Microscopy
5-Toxicology
6-Biological production and viral load monitoring
7-Particle analysis
8-Structural biology
9- 3D tissue imaging
10-Virology
L.A. SURA SALAH
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