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1. TRANSMISSION ELECTRON
MICROSCOPE
Presented by:
Rajkamal Mohan
(CHP15111)
Tezpur University

2. CONTENTS
 Introduction and History
 Theoretical Background
 Instrumentation
 Sample Preparation
 Drawbacks of TEM

3. Introduction
 Microscopes are used to see objects that cannot be seen
by naked eyes.
 The range can be between mm to nm.
 There are three main microscopic techniques:
 Optical Microscopy
 Scanning Probe Microscopy
 Electron Microscopy

4. Transmission Electron Microscopy
(TEM)
 Transmission electron microscopy (TEM) is a microscopy
technique where a beam of electrons is transmitted
through a ultra thin specimen. An image is formed from
the interaction of the electrons transmitted through the
specimen; the image is magnified and focused onto an
imaging device, such as a fluorescent screen, on a layer of
photographic film, or to be detected by a sensor such as a
CCD camera.

5. History
 1897
 1924
 1929
 1931
 1934
J.J Thompson
Louis deBroglie
E. Ruska
Knoll & Ruska
Driest & Muller
 1938 von Borries & Ruska

Discovers electron
Identifies wavelength for electron
Ph.D thesis on magnetic lenses
1st electron microscope built
Surpass resolution of the light microscope (LM)
First practical electron microscope (EM)
Seimens : 10 nm resolution
J.J Thompson
L. deBroglie E. Ruska M. Knoll

6. Theoretical Background
 Why we need Electron Microscope?
 Light microscopes are limited by the physics of light to 500x or 1000x
magnification and a resolution of 0.2 micrometers.
 In the early 1930's there was a scientific desire to see the fine details
of the interior structures of organic cells (nucleus, mitochondria...etc.).
 This required 10,000x plus magnification which was just not possible
using Light Microscopes.

7. LM, resolving power ~0.25µm, maximum
(useful) magnification is about
250µm/0.25µm = 1000X.
Any magnification above this value
represents
empty magnification
TEM at 60,000 volts has a resolving power
of about 0.0025 nm. Maximum useful magnification
of about 100 million times

8. Difference between light microscope
and electron microscope
FEATURES LIGHT MICROSCOPE ELECTRON MICROSCOPE
Electromagnetic
spectrum used
Visible light
760nm (red) – 390nm
Colours visible
Electrons
app. 4nm
Monochrome
Maximum resolving
power
approx. 200nm 0.2nm
Maximum magnification x1000 – x1500 x500 000
Radiation source Tungsten or quartz
halogen lamp
High voltage (50kV)
tungsten lamp
Lenses Glass Magnets
Interior Air-filled Vacuum
Focusing screen Human eye (retina),
photographic film
fluorescent (TV) screen,
photographic film

9. Instrumentation
 TEM characterizes samples simultaneously by diffraction
and imaging techniques.

10. Instrumentation (Contd.)
 In a conventional transmission electron microscope, a thin
specimen is irradiated with an electron beam of uniform current
density.
 Electrons illuminate the specimen through a condenser lens
system.
 Objective lens provides the formation of either image or diffraction
pattern of the specimen.
 The electron intensity distribution is magnified with a lens system
and viewed on a fluorescent screen. The image can be recorded by
an image plate or digitally by a CCD camera.

11. Design of Transmission Electron
Microscope
A simplified ray diagram of a
TEM consists of an electron
source, condenser lens with
aperture, specimen, objective lens
with aperture, projector lens and
fluorescent screen.

12. Electron Gun
Electron beam is generated in the electron gun. Two basic types of
guns are used:
1. Thermionic Gun:
Based on two types of filaments: Tungsten(W) and Lanthanum
Hexaboride(LaB6).
2. Field Emission Gun(FEG):
Employs either a thermally assisted cold field emitter or Schottky
emitter.

13. Condenser Lens
 Illuminates the specimen.
 Relatively weak lens.
 Longer focal length than objective or projector lens.
 May bring electron beam into focus directly upon
specimen, above the specimen (over focusing) or below
the specimen (under focusing).

14. Objective Lens
 Strong lens
 It has highly concentrated magnetic field and short focal
length.
 Total magnification in the TEM is a combination of the
magnification from the objective lens times the
magnification of the intermediate lens times the
magnification of the projector lens. Each of which is
capable of approximately 100x.
 Mob X Mint X Mproj = Total Mag

15. Fluorescent Screen
 In TEM, screen coated with a material in the visible range, eg zinc
sulphide, is installed beneath the projector lens in the path of the
electron beam.
 Screen emits visible light when bombarded with electrons.

16. Vacuum System
 Electron can’t travel more than a few angstrom without
colliding with gas molecules.
 Distance between photographic plate and electron gun is
approximately 1 meter.
 Two types of vacuum pump are used
1. Rotary (mechanical) pump.
2. Diffusion pump (Oil or Mercury)

17. Some typical TEM models

18. TEM Sample Preparation
The TEM sample should be thin, so special care must be taken
while cutting a thin slice so that the specimen is not deformed
during its preparation. Some common techniques are:-
a) SPARK CUTTER: - In this, electric discharge between a wire and
the specimen is used to cut the metal by removing small
particles of metal from the surface of the specimen.
b) FOCUSED ION BEAM (FIB):- A thin slice of the sample is cut by
an ion beam on a scanning ion microscope. The main
advantage of this method is that it allows selective
thinning at desired locations by cutting trenches in the
sample.

19. TEM Sample Preparation
Some basic requirements
 Cleaning the surface of the specimen
 The proper cleaning of the surface of the sample is important because
the surface can contain a variety of unwanted deposits, such as dust,
silt, media components or other contaminants.
 The best way to clean the surface of specimen from contaminants is to
carefully rinse them three times for 10 min in 0.1M cacodylic acid
buffer (pH 7.3) at room temperature.

20. TEM Sample Preparation
 Fixatives
 Are chemicals that denature and precipitate cellular
macromolecules.
 Primary fixation of the specimen
 Fixation can be achieved by perfusion and
microinjection, immersion with vapours using various
fixatives including aldehydes (glutaraldehyde), osmium
tetroxide, tannic acid.

21. What information can TEM provide?
RECTIONS ON THE
BOTTOM
SIDE ARE EXAMINED
IN THIN OR FOIL
SPECIMEN
(TEM)

22. What information can TEM provide?
 Thickness of the specimen: The transmission of
unscattered electrons is inversely proportional to
the specimen thickness.
 Orientation, atomic arrangements and phases
present:
Given by incident electrons that are scattered by
specimen atoms in an elastic fashion. These
electrons follow Bragg's Law
nλ=2dSinθ
The incident electrons that are scattered by the
same atomic spacing will be scattered by the same
angle. These scattered electrons can be collated
using magnetic lenses to form a pattern of spots;
each spot corresponding to a specific atomic
spacing (a plane). Diffraction pattern of a
monocrystalline sample
Selected area electron diffraction

23. What information can TEM
provide?
 Inelastically scattered electrons can be utilized in two ways: Electron Energy Loss
Spectroscopy (EELS) and Kikuchi Bands.
 Elemental composition and atomic bonding state:
Determined by analyzing the energy with spectroscope attached under the
electron microscope (Electron Energy Loss Spectroscopy). By selecting electrons with a
specific loss energy, element distribution in specimen can be visualized.
 Kikuchi lines: Bands of alternating dark and bright lines related to the atomic spacing
of the specimen. Appear in transmission electron diffraction patterns of relatively
thick crystals due to Bragg reflection of inelastically scattered electrons.
The Kikuchi lines pass straight through
the transmitted and diffracted spots.

24. Limitations of TEM
 Sampling:
 Very small sample size. But fortunately we are dealing with nanostructures.
 Interpreting transmission images:
 TEM presents 2D images of 3D specimens.
 Electron Beam damage and Safety:
 TEM is a potential dangerous instrument that generates radiation level that is
enough to kill human being.
 Specimen preparation:
 Your specimens have to be thin, very thin (has to be electron transparent) if you are
going to get any information.

25. Examples of TEM images
Matrix - β'-Ni2AlTi
Precipitation in an Al-Cualloy
Dislocations in superalloy

26. References
[1] William R. Herguth, President, Guy Nadeau.Applications of Scanning Electron
Microscopy and Energy Dispersive Spectroscopy (SEM/EDS) To Practical Tribology
Problems. Senior Technical Associate Herguth Laboratories, Inc.
[2] R.F. Egerton. Electron Energy-Loss Spectroscopy in the Electron Microscope.
[3] M.Von Heimendahl, W.Bell, G.Thomas. Applications of Kikuchi line Analyses in
Electron Microscopy. Journal of Applied Physics 35 (1964) 3614.
[4] C. Richard Brundle, Charles A. Evans Jr, Shaun Wilson. Encyclopedia of materials
characterization, Butterworth-Heinemann publications, 1992.
[5] Joachim Mayer, Lucille A. Giannuzzi, Takeo Kamino, and Joseph Michael. TEM
Sample Preparation and FIB-Induced Damage. Mrs Bulletin, volume 32, May 2007

27. THANK YOU