Transmission Electron Microscope (TEM)
Transmission electron microscopes
are laboratory equipments that facilitate observation of objects that are
otherwise too small to be viewed by a normal microscope (as well as the naked
eye) -- of the order of 2.5Å (Å, or angstrom, is one ten-billionth of a meter).
These microscopes operate on the same basic concept as a light microscope with
the only difference being that they use an electron beam instead of light.
How does a Transmission electron Microscope work?
When an electron beam is passed
through a very thin slice of the specimen, it interacts with the atoms of the
specimen. This results in the scattering of electrons (technically referred to
as diffraction of the electron wave) – since electrons have both particle and
wave nature, when the electron beam hits the specimen, some electrons are not
only get reflected or change their trajectory, but the resulting wave of the
electron beam is also altered. This can be mapped as an image using
magnification and focusing techniques and observed on a fluorescent screen. The
only limitation of this technique is the need for extremely thin observation
samples that can aid the required electron transmission.
Functions of a Transmission Electron Microscope
Studying of Material
Microstructure
Transmission electron microscopes
are used to study the fine structural characteristics that can only be observed
at large magnification levels and therefore need a high resolution capability.
Morphology information of materials, their microstructure as well as their crystal
structure can be studied using this technique, since they facilitate in
characterizing the microstructure of materials, since they have a high spatial
resolution (it is the number of pixel points per unit length that can be
independently observed under magnification – it is a property of the material
composition and structure and not the imaging instrument).
Fractural Analysis of
Materials
Transmission electron microscope
can also help scientists, geologists, forensic experts and civil engineers in
structural analysis of fractures that can occur in various materials (such as
rock, steel or concrete), by helping observe their fine structure. The
mechanical properties of such materials such as ductility, brittleness,
inter-granularity, and fatigue induced fractures can be studied by imaging the
micro-fractographic patterns (patterns formed in the material’s microstructure
as a result of fracture) of such materials.
Viral Diagnosis
A transmission electron
microscope is also used in the medical profession to classify viruses according
to their genome structure, morphological features and protein composition.
Viruses cannot be seen with normal microscopes, as a result of which diagnosis
is extremely difficult (because of lack of appropriate pathology or tests). TEM
is however a useful instrument for observing them, given their high resolution
capability. TEM has therefore become an extremely useful medical tool for
studying infected lesions, biopsies, and excreta and has proved to be effective
in providing quick ante-mortem and post-mortem diagnoses.
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