Thursday, December 5, 2013

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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