B . TECH BIOTECH

1. PHYSICS ACTIVITY
ELECTRON AND OPTICAL
MICROSCOPE
TEAM MEMBERS : 54. D. PIRATHEEP SEKAR
57. D.N.VAISNAVI
59.C.JENANISANKARI

2. CONTENTS :
 ELECTRON MICROSCOPE
 TYPES OF ELECTRON MICROSCOPE
 PRINCIPLE OF TEM AND SEM
 CONSTUCTION AND WORKING OF TEM AND SEM
 ADVANTAGES AND DISADVANTAGES
 APPLICATIONS
 OPTICAL MICROSCOPE
 TYPES OF OPTICAL MICROSCOPE
 PRINCIPLE AND WORKING OF OPTICAL MICROSCOPE
 DIFFERENCE BETWEEN OPTICAL AND ELECTRON
MICROSCOPE

3. ELECTRON MICROSCOPE
 The first electron microscope was
invented by ERNST RUSKA , in the year
1933.
 He was awarded the NOBLE PRIZE FOR
PHYSICS in the year 1986.
 Electron microscope is divided into two
types .
 They are
 Transmission electron microscope
 Scanning electron microscope

4. PRINCIPLE OF TEM AND SEM
TEM:
Principles of Transmission Electron Microscopy.
Illumination - Source is a beam of high velocity electrons accelerated
under vacuum, focused by condenser lens (electromagnetic bending
of electron beam) onto specimen.
SEM:
A scanning electron microscope (SEM) is a type of electron
microscope that produces images of a sample by scanning it with a
focused beam of electrons. The electrons interact with atoms in the
sample, producing various signals that contain information about the
sample's surface topography and composition.

5. CONSTRUCTION OF TEM:
 It consists of an electron gun to produce electrons.
 Magnetic condensing lens is used to condense the
electrons and is also used to adjust the size of the
electron that falls on to the specimen.
 The specimen is placed in between the condensing
lens and the objective lens .
 The magnetic objective lens is used to block the high
angle diffracted beam and the aperture is sued to
eliminate the diffracted beam (if any) and in turn
increases the contrast of the image.
 The magnetic projector lens is placed above the
fluorescent screen in order to achieve higher
magnification,.
 The image can be recorded by using a fluorescent
(Phosphor) screen or (CCD – Charged Coupled device)
also.

6. WORKING OF TEM:
 Stream of electrons are produced by the electron gun and is made
to fall over the specimen using the magnetic condensing lens.
 Based on the angle of incidence the beam is partially transmitted
and partially diffracted. Both these beams are recombined at the E-
wald sphere to form the image. The combined image is called the
phase contrast image.
 In order to increase the intensity and the contrast of the image, an
amplitude contrast has to be obtained. This can be achieved only by
using the transmitting beam and thus the diffracted beam can be
eliminated.
 Now in order to eliminate the diffracted beam, the resultant beam is
passed through the magnetic objective lens and the aperture. The
aperture is adjusted in such a way that the diffracted image is
eliminated. Thus, the final image obtained due to transmitted beam
alone is passed through the projector lens for further magnification.
 The magnified image is recorded in fluorescent screen or CCD. This
high contrast image is called Bright Field Image.
 Also, it has to be noted that the bright field image obtained is purely
due to the elastic scattering (no energy change) i.e., due to
transmitted beam alone.

7. CONSTRUCTION OF SEM:
It consists of an electron gun to produce high
energy electron beam.
A magnetic condensing lens is used to condense
the electron beam and a scanning coil is arranged
in-between magnetic condensing lens and the
sample.
The electron detector (Scintillator) is used to collect
the secondary electrons and can be converted into
electrical signal.
These signals can be fed into CRO through video
amplifier .

8. WORKING OF SEM:
 Stream of electrons are produced by the electron gun and these
primary electrons are accelerated by the grid and anode. These
accelerated primary electrons are made to be incident on the sample
through condensing lenses and scanning coil
These high speed primary electrons on falling over the sample
produces low energy secondary electrons. The collection of secondary
electrons are very difficult and hence a high voltage is applied to the
collector.
These collected electrons produce scintillations on to the photo
multiplier tube are converted into electrical signals. These signals are
amplified by the video amplifier and is fed to the CRO.
By similar procedure the electron beam scans from left to right and the
whole picture of the sample is obtained in the CRO screen.

9. ADVANTAGES AND DISADVANTAGES OF TEM AND SEM
ADVANTAGES OF TEM AND SEM
TEM:
 very high resolution power
 Information about crystal
structure and chemical
composition can be collected
simultaneously.
SEM:
 Image can be directly viewed.
 Has large depth of focus.
DIADVANTAGES OF TEM AND SEM
TEM:
 Aberrations due to lenses.
 No 3D image is formed.
SEM:
 The resolution of image is poor.
 Preparation of samples are
difficult and tedious.

10. APPLICATIONS
TEM:
 In nano science, to find internal
structure of nanomaterials
 To get 2D image of biological
cells , virus ,bacteria,etc…
 In studying the composition of
paints and alloys
 used in biology related fields
like microbiology etc…
SEM:
 specimens of large thickness
can be verified.
 used to get 3D image of
biological cells , DNA , bacteria..
 To find the structural
composition of paper pulps ,
ceramic materials , polymers
etc…

11. OPTICAL MICROSCOPE (LIGHT MICROSCOPE):
SIMPLE MICROSCOPE:
 A simple microscope uses a lens
or set of lenses to enlarge an
object through angular
magnification alone, giving the
viewer an erect enlarged virtual
image.[3][4] The use of a single
convex lens or groups of lenses
are still found in simple
magnification devices such as
the magnifying glass, loupes,
and eyepieces for telescopes and
microscopes.

12. OPTICAL MICROSCOPE:
COMPOUND MICROSCOPE:
 A compound microscope uses a lens
close to the object being viewed to
collect light (called the objective lens)
which focuses a real image of the
object inside the microscope . That
image is then magnified by a second
lens or group of lenses (called the
eyepiece) that gives the viewer an
enlarged inverted virtual image of the
object .5

13. View from simple View from compound

14. DIFFERENCE BETWEEN OPTICAL AND ELECTRON
MICROSCOPE:

15. REFERENCES:
 WIKIPEDIA
 http://www.imina.ch/applications/optical-microscopy
 www.steetguidedic.co.in
 https://www.jic.ac.uk/microscopy/intro_EM.html