2. TRANSMISSION ELECTRON MICROSCOPE (TEM)
Principle:-
beam of electrons pass through sample
magnified image get displayed in photographic film
magnetic lenses of short focal length is used for large
magnification.
Construction:-
Electron gun, electromagnetic condensing lens , object holder,
electromagnetic objective and projective lenses and
photographic plate or fluorescent screen are used in TEM.
3. Working:-
• Electrons are highly accelerated from
the electron gun.
• It is condensed into a beam of electrons
with help of condensing lens.
• Condensed beam of electron will pass
through the thin specimen.
• Electromagnetive Objective and
Projective lenses will produce the final
image on the fluorescent screen.
• The final image will be 200000x large.
4. • Condensing lens consist of current carrying coil produces
magnetic field(acting lens)
Magnetic field focus the beam of electrons on specimen
• The focal length can be varied by varying the current
through coils.
• Velocity of the electrons varied by accelerating potential
difference
• When the beam is incident on the sample , some is
transmitted and focused by objective lens
• The high angle diffracted electrons are blocked by aperture
there by increase the contrast
• The beam passed through projective lens and projected on
fluorescent screen.
5. Uses:-
To investigate atomic structure and structure of crystals.
Used in biology, physics, chemistry , etc…
For the study of textile fibres , purification of lubricant oils and composition
of paper and paints.
Disease causing viruses.
Merits:-
High Resolution.
It has high resolving power upto 1 A to 2A.
Specimen size upto 0.2nm can be examined.
100000 times greater than the size of the object magnification can be
obtained.
6. Demerits:
• Not suitable for very thin sample.
• Not suitable for thick objects.
• The 3D image of the object cannot be obtained.
• Highly Expensive.
THANK YOU
