transmission electron microscopy

1. TRANSMISSION
ELECTRON
MICROSCOPY

2. INTRODUCTION
• It is an electron microscopy technique.
• Direct imaging of NPs is possible.
• Provides information about the atom distribution in and on the surface
of the nanocrystal.

3. TEM image of a green leaf TEM image of Golgi apparatus
TEM image Cytoplasm of liver TEM image of blood platelet

4. SCHEMATIC DIAGRAM

6. COMPONENTS
Illumination system
Specimen stage
Objective lens system
Magnification system
Data recording system
Chemical analysis system

7. ILLUMINATION SYSTEM
 Consists of electron gun.
 LaB6 thermionic emission source
 Condenser lens-forms fine electron probe
SPECIMEN STAGE SYSTEM
 Structural analysis
 Performs in-situ observations
 Phenomena induced-annealing electric field or mechanical stress thereby
helping in characterization.

8. OBJECTIVE LENS SYSTEM
 Determines the limit of image resolution
MAGNIFICATION SYSTEM
 Consists of intermediate lenses and projection lenses.
 Magnification – 1.5 million
DATA RECORDING SYSTEM
 Using CCD
 Data processing and quantification

9. CHEMICAL ANALYSIS SYSTEM
 Using EDS / EELS
 Used to quantify the chemical composition of the specimen
and the electronic structure.

10. SAMPLE PREPARATION
Involves 4 steps
1. Processing
 Fixation-Prevent further deterioration using glutaraldehyde.
 Rinsing-Washed with sodium cacodylate buffer that maintains the pH of 5.1-
7.4
 Post fixation-Secondary fixation with osmium tetroxide (OsO4) which is
to increase the stability and contrast of fine structure.
 Dehydration- Water content in the tissue sample should be replaced with an
organic solvent since the epoxy resin used in infiltration and embedding step
are not miscible with water.
 Infiltration-Epoxy resin is used to infiltrate the cells.

11. 2. Embedding
3. Polymerization
4. Sectioning - Specimen must be cut into very thin sections for electron
microscopy so that the electrons are semitransparent to electrons.

12. INSTRUMENT

13. WORKING
ELECTRON GUN
 Emits electrons from a cathode
 Then accelerating them through an anode
 Electrons pass through an aperture into the vacuum tube
ELECTROMAGNETIC LENSES
 Used to control electron beam
 Formed by coils around the tube
 Direct the electron beam through the center of the tube to a very thin
specimen located part-way down the tube.

14. Schematic diagram of working

15. • Formation of an image of the specimen is possible because the
electrons in the beam are affected by different regions of the specimen
in different ways:
 Some parts of the specimen might allow electrons to pass through
unaffected.
 Other regions within the specimen absorb some or all of the
electrons that reach them.
 Some parts of the specimen may cause the electrons to "bounce off in
different directions" - that is, to scatter the electrons.
• Image is formed when they reach an image plane where they are
detected by a suitable sensitive material such as a fluorescent film.
• The image produced is a greyscale image.

16. ADVANTAGES
•Offer the most powerful magnification, potentially over one million times
or more
•Provide information on element and compound structure
•Images are high-quality and detailed
•:Yield information of surface features, shape, size and structure
•They are easy to operate with proper training.

17. DISADVANTAGES
• TEMs are large and very expensive
• Laborious sample preparation
• Potential artifacts from sample preparation
• Samples are limited to those that are electron transparent, able to
tolerate the vacuum chamber and small enough to fit in the chamber
• TEMs require special housing and maintenance
• Images are black and white.

18. APPLICATIONS
• TEMs provide topographical, morphological, compositional and
crystalline information.
• View samples on a molecular level
• Useful in the study of crystals and metals

19. REFERENCE
• Z. L. Wang, “Characterization of nanophase materials”, Wiley
Interscience International, 2001 pg. no-37 to 56.
• Virtual amrita laboratories .