This document discusses different types of microscopes, focusing on electron microscopes. It describes how electron microscopes like transmission electron microscopes (TEM) and scanning electron microscopes (SEM) work using electron beams instead of light, allowing them to achieve much higher magnifications. TEMs transmit electron beams through thin samples to view internal structures, while SEMs scan surfaces with electron beams to produce 3D images. Electron microscopes are important tools for viewing viruses, cells, and other microscopic structures.

1. ELECTRON
MICROSCOPES
T.PREMKUMAR
II M.SC., BIOINFORMATICS
ALAGAPPA UNIVERSITY

2. MICROSCOPY
♣ microscope is an optical system designed for the study of minute objects which
cannot be seen in our naked eyes.
♣Types of microscopes
♣ There are three types based on the source of illumination
1. Light microscopes
2. Electron microscopes
3. X-ray microscopes

3. ELECTRON MICROSCOPES
A system of electromagnetic coils where electron beam is used as
the source of illumination.
Wave length of electron is very short(0.05A).
The magnification is very high.
Studying virus ,bacteria ,and ultra structure of cell organelles.
The first microscope designed by Knoll and Ruska.

4. Types of electron
microscopes
♣ Transmission electron microscope (TEM)
♣ Serial-section electron microscopy (ssEM)
♣ Scanning electron microscope (SEM)
♣ Reflection electron microscope (REM)
♣ Scanning transmission electron microscope (STEM)

5. IMAGE OF BACILLUS SUBTILIS TAKEN WITH A
1960S ELECTRON MICROSCOPE.

6. Structure
 The electron microscopes consists of following components ;
 1. electron gun
 2. condenser lens
 3. object
 4. objective lens
 5. amplifier lens
 6. projector coils
 7.Flurescent screen (or) photographic plate
 8. vaccum tube
 9. cooling system

7. TEM, SEM
 Transmission electron microscope (TEM)
In TEM the electron beam is transmitted through the ultra thin object
 Scanning electron microscope (SEM)
 In SEM the electron beam is scanning the surface of the objects and conveys its
image to a TV screen

8. Transmission electron microscope
 Electron beam is passed through the specimen to produce its
image is called TEM
 The first TEM was designed by max knoll and Ernst ruska in 1931
 Available in the market in 1939
 Tem used in the research on virology,oncology,pollution
studies,materiels science ,semi-conductor research.

9. Principle
 The basic principle of electron microscopy similer to the optical principle of
ordinary microscope .
 When high voltage of electric current is passed through filament of cathode ray
tube ,electron beams are produced from the filament .
 An electron passed a specimen stained with metallic gold or osmium,the
specimen absorbs some rays ,reflect some rays and leaves some rays to pass
through it .
 The interaction between the specimen and electrons in the beam produced
 The image is collected by an objective lens(electro magnetic coils) and magnified
by an amplifier(another electro magnetic coil) .

10.  The image due to electron distribution cannot be seen with naked eyes, so the
images is recordor on the screen or photograbic plate or camera
 Wavelength of electron beam is very short (0.05aor 0.005nm)
 TEM has higher resolving power than the compound microscope

11. Tem view of pollen grains

12. Instrumentation
Electron Gun
 It’s a source of illumination
 V shaped filament and two circuler plates with holes in the centre .
 The two plates named as Anode plate and cathode shield .
 A high current pass through anode plates , causing it’s to emmiting electrons .
 The electrons are attracted anode plate and they pass through the hole in centre
 Condenser lens
 There are two types of lens
 Each lens has coils wire called electromagnetic coils or electromagnetic lens .
 They make electron beam very narrow and focus the beam in object .

13.  3. Object :
 The object placed below the second condenser lens in the focus length of beam .it’s supporting film
and mounted on a copper grid
 4. Objective lens:
 It’s another electromagnetic coil , placed below the object .
 Capture the transmitted electrons from the object and magnifies the images
 5. Amplifier lens :
 It amplifies the images produced by the objective coil .
 6. projector lens :
 It projects the final images on the screen
 7. flurescent screen :
 It’s receives the final images on the object on a photographoic flim , and it’s developed to make a
microphotograph .

14.  8. Vaccum tube :
 The entire set_up is placed in a vaccum tube ,because the electron move in straight line only in a
vaccum .
 9. cooling system :
 Continuously current is flowing through the electromacnatic coil . So the coils get heated .the water
circulating around the vaccum tube .

15. Applications of TEM
#topograoy
The surface fetures of the objects
#morphology
The shape and size of the particles
#Composition
The elements and compounds objects is composed
#crystallographic information
How the atom arranged in the objects
 1. TEM is an ideal tool for the study of ultra structure of cells
 2. used in identification of plant and animal virus based on the
structural features
 3 . Also used in cancer research for the cytological observation of
cancer cells .

17. scanning electromicroscope (SEM)
 A scanning electron microscope (SEM) is a type of electron
microscope that produces images of a sample by scanning the surface with a
focused beam of electrons.
 The electrons interact with atoms in the sample, producing various signals
that contain information about the surface topography and composition of the
sample.
 The most common SEM mode is detection of secondary electrons emitted by
atoms excited by the electron beam.

18. principle
◘ the SEM also uses an electron beam as illumination and electromagnetic coils to direct of the path
way .
◘ when electron beam is focused on the specimen ,it’s produces secondary electrons (SE), back
scattered electrons (BSE)and characteristics Xrays .
◘ The BSE gives the information about the distribution of different elements in the sample.
◘ The electrons reflected by the sample due to elastic scattering propertys are called back scattered
electrons (BSE).
 Characteristics x-rays are emitted by the sample when the electron beam remove electrons in the
inner cell .
 The se and bse and characteristic x-ray are detected accurately used separate specialized detectors
.
 Amplifier used to detect the electric signals .
 Electronic amplifiers of kind(collector ,scintillator ,and PMT) are used to measure the electric signals
 The signals are converted into bright spots of variying density by a scanning circuit to give images .

21. Sem view of ant

22. Applications of SEM
 Sem is very useful to view the surface architecture of
microscopic creatures like bacteria ,diatoms ,pollen
grains ,and others
 Sem gives 3D- structure of objects to reveal the structure
of the organism or organelles .
 Sem is employed in the analysis of structural fetures
compound eyes of insects
 Hairs and scales on plant and animal surface are
characterized with the SEM
 SEM is used to study the surface of small archeological
specimens and fossils