1. Transmission electron microscopes use electrons instead of light to image samples, allowing for much higher resolution down to the nanometer scale. 2. The wavelength of electrons can be decreased by increasing the accelerating voltage, improving resolution according to the Rayleigh criterion. 3. Factors like vacuum quality, beam alignment, and sample thickness influence image quality in transmission electron microscopy.

2. Micros (small) skopos (to look at) = microscope
O.2 mm 0.2 m 0.2 nm
Resolving power
The ability to make points or lines which
are closely adjacent in an object distinguishable in
an image.

3. Why use electrons?
The “resolving power” of our naked eyes is ~ 0.1-0.2 mm.
Image resolution (R) in TEM in terms of the classical
Rayleigh Criterion:
R  1

λ = wavelength of radiation
λ in the Visible = 400 - 800 nm R ~ 200 - 400 nm
SEM Image of a CD
Cd
Dvd
HD Dvd
Blue ray
800 nm
400 nm
200 nm
150 nm

4. Some fundamental properties of electrons
In the TEM we impart momentum to the electron byaccelerating
them it through a potential drop (V),giving it a kinetic energy:
Based on de Broglie’s ideas of the wave-particle duality,
we can relate the particle momentum (p) to its wavelength(λ)
through Plank’sconstant:
V = Acceleratingpotential
m0= electron mass
v = velocity
  h
p
2
m 2
eV  0v

5. We also knowthat: p=m0v
So: p  2m0eV
This leads to the relationship between the electronwavelength
and the acceleration voltage:
h
2m0eV

By increasing the acceleration voltage we decrease the
wavelength of the electrons, therefore increasing theresolution

6. If we want to include the relativisticeffects:











2
0 
0
2m c
eV
2m eV 1
h

- 1.602 X 10-19 C
1.602 X 10-19 J
9.109 X 10-31kg
511 keV
1.602 X 10-19 N m (for 1 volt potential)
6.626 X 10-34 N m s
Charge(e)
1 eV
Rest mass (m0)
Rest energy (m0c2)
Kinetic energy (charge X voltage)
Planck’s constant (h)
Speed of light in vacuum (c) 2.998 X 108 m/sec
Fundamental Constants and Definitions
Electron at 100 kV
have the wavelength
and the
resolution of
We cannot make
perfect electron lenses
for getting this
resolution
Voltage Relativistic
100 kV
120 kV
200 kV
300 kV
0.0037 nm
0.0034 nm
0.0025 nm
0.0020 nm

8. TEM
Vibration isolation

9. W Tip
LaB6

11. 1. High monochromatic
electron beam
2. Good vacuum to avoid
electron scattering
3. Good alignment of electron
beam
4. Magnification Calibration
5. Specimen preparation (10
to 150 nm electron
transparent)
Parameters for good Imaging

12. User-Mechanical
Examples of Environmental “Artifacts”
Aperiodic - Vibrational
Periodic - EM Fields
User-Acoustic

13. Source
Thermoionic Field Emission
W
Thermoionic: if we heat a metal to a high enough temperature, we
can give the electrons sufficient energy to overcome the natural
barrier (the work function ) that prevents them from leakingout.
LaB6 Schottky Cold FEG

14. kT
 
J  AT 2
e
J = current density from the source
T = operating temperature (K)
A = Richardson’s constant (A/m2 K2) – (it depends on thematerial)
k = Boltzmann’s constant (8.6 X 10-5eV/K)
Φ – Work Function of the materials
Thermoionic sourcesare:
-High melting point materials (i.e. WTm=3660K)
-Low low work function materials (i.e. LaB6 or W)
(ΦW= 4.5eV;ΦLaB6=2.4eV

15. Undersaturated
and aligned Saturated
Undersaturate
d and
misaligned

16. Field Emission Guns
The strength of an electric field E is considerably increasedat
sharp points.
If we have a voltage V applied to a point of radiusr:
E  V
r
Toallow field emission, the surface has to be pristine (freeof
contaminants and oxides)
i.e. We operate in UHV (<10-11 Torr,10-8 Pa)

17. Characteristics of the Electron Beam
Brightness Coherency
➢diameter(d0)
➢cathode emission current(ie)
➢angular distribution of the electrons (α0 semiangle)

18. Brightness:
0
2
(
d0 )2
( )2
ie
 
Source solid angle
Beam Current Density
i.e. intensity
(current/unit area)
The higher is β:
- the more information we can get (more electrons in a beam of a give size)
- The more damage we can produce in the sample

19. Coherency: how well in phase the electron wavesare?
Full coherency: monochromatic source
Coherence length (c):
c
E

h
v = electron velocity
ΔE = Energy spread of the beam
h = Planck’s constant

20. Spatial Coherency: related to the size of thesource
Perfect spatial coherence would imply that the electronsare
emanating from the very same point at thesource
Effective source size: dc


the accelerating voltage (increase)
2
 = electronwavelength
α = angle subtended by the source at the specimen
Tomaximise coherency we can:
➢make the source size dc smaller (by using a field-emission gun)
➢Use a small illuminationaperture
➢If the source size is big (W or LaB6)decrease

22. TEM Grids

24. SAED Pattern

25. Sample Preparation

26. Diamond wheel saw
• Diamond wheel saw is used to cut ~
0.2 to 0.5 mm thick pieces from
sample
• A diamond wafering blade along with
cooling/lubrication system is used for
this purpose
• Lubrication is used for optimum
cooling at high cutting speeds for
extremely hard or tough materials

35. References:-
1]Transmission Electron Microscopy: A Textbook for Materials Science, by C. Barry Carter
and David L. Phillips
2] Conventional transmission electron microscopy, by Mark Winey and Thomas H.
Giddings, doi: 10.1091/mbc.E12-12-0863
3] Web resources

36. Thank you