Typesofelectronmicroscope 130703030654-phpapp01

 An electron microscope is a microscope
that uses a beam of accelerated electrons as
a source of illumination.
 As the wavelength of an electron can be up
to 100,000 times shorter than that of visible
light photons,
 electron microscopes have a
higher resolving power than light
microscopes and can reveal the structure of
smaller objects.

 Electron microscopes are used to
investigate the ultrastructure of a wide
range of biological and inorganic
specimens
including microorganisms, cells,
large molecules, biopsy samples, metals
, and crystals.

Types
There are two main electron microscopy
techniques:
Transmission electron microscopy,
which essentially looks through a thin
slice of a specimen.
Scanning electron microscopy, which
looks at the surface of a solid object.

Transmission Electron
Microscope
 The Original Form of EM that uses the
high voltage Beam of Electrons to create
an image.
 Its has Resolution power up to
0.5 angstrom (50 picometres).
 Most Powerful for observing
minute objects

Mechanism
 Electron Gun Produces Beam of 100 keV.
 Anode and Cathode accelerate Beam.
 Focusing occur by Electrostatic and
electromagnetic lenses
 Beam strikes the sample and pass through
it.
 After emerging out it carries information
about Sample and magnify it by objective
lens
 Information can be analyzed by Screen or
Film or CCD Cameras on LCD or monitor.

Advantages
 TEMs offer the most powerful
magnification, potentially over one million
times or more
 TEMs provide information on element and
compound structure
 Images are high-quality and detailed
 TEMs are able to yield information of
surface features, shape, size and structure
 They are easy to operate with proper
training

Limits of TEM
 High Voltage can damage Sample.
 Sample should be extremely thin upto
100 nm.
 Bio Samples are Dehydrated ,
chemically fixed, embedded in polymer
resin to stabilize them.
 Staining is required to highlight in order
to achieve require image contrast.

Scanning Electron Microscope
 SEM produces the image by scanning it
with focus beam of electron.
 Electrons interact with electrons in
sample and convey information in form
of signals to detectors. E.g. topography
& sample surface.
 SEM can achieve resolution better than
1 nanometer.

Mechanism
 When High energy Electrons strikes the
surface, it lose energy by diff.
mechanisms like heat, emission of low
energy secondary electrons and high
energy backscattered electrons.
 X-ray or light emerges from sample that
carries information on it.

Advantages
 Its basically used for biological samples
 It can scan the processes occurring on
surface and tells about topography and
composition.
 Enable us to view without thinning
dehydrating fixing the sample
 Can scan bulk samples upto 2-3 cm which
can not be examined by TEM.
 View obtained is in 3D.
 ESEM produce image of Wet, gas &
Vacuumed Samples and biological samples.

Sample preparation
1.Chemical fixation-
formaldehyde and glutaraldehyde,
and lipids with osmium tetroxide.
2. Negative stain – suspensions containing
nanoparticles or fine biological material (such as
viruses and bacteria) are briefly mixed with a
dilute solution of an electron-opaque solution.
3. Cryofixation – freezing a specimen so rapidly,
in liquid ethane, and maintained at liquid nitrogen
or even liquid helium temperatures, so that the
water forms vitreous (non-crystalline) ice.

disadvantages
 Electron microscopes are expensive to
build and maintain.
 The samples largely have to be viewed
in vacuum.

Typesofelectronmicroscope 130703030654-phpapp01

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