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
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.
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.
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 .